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| \relax | |||
| \@writefile{toc}{\contentsline {section}{\numberline {1}Overview}{1}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {2}Work Log}{1}} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {2.1}I2C OLED display}{1}} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {2.2}Internal AVR Temperature Sensor}{1}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {3}Wiring Pinout is wrong on Internet - Cable has labels}{2}} | |||
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| []\OT1/cmtt/m/n/10.95 I'm on Linux here and found that the readily-available Im | |||
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| \documentclass[11pt]{article} | |||
| %Gummi|065|=) | |||
| \title{\textbf{Car Stereo Replacement}} | |||
| \author{Steak Electronics} | |||
| \date{10/27/19} | |||
| \begin{document} | |||
| \maketitle | |||
| \section{Overview} | |||
| Replacing a car stereo. | |||
| \section{Work Log} | |||
| \subsection{I2C OLED display} | |||
| Just for fun, I bought an I2C oled display and are going to use it to display something. Notes on this: | |||
| Using the adafruit SSD1306 and GFX library (this procedure is well covered in other places), you can load an example sketch and get it running. First thing to change is to remove the Adafruit logo and replace it with my own. Let's do that. | |||
| From https://design.goeszen.com/convert-image-for-oled-display.html | |||
| \begin{verbatim} | |||
| I'm on Linux here and found that the readily-available ImageMagick package will do the trick for you without any scripting. And runs on the CLI! Simple as that: | |||
| convert some_image.png some.image.mono | |||
| \end{verbatim} | |||
| That's efficient. But it didn't really work out. Too much work, I don't need it that bad. Have to convert it to something the c compiler can read. | |||
| \subsection{Internal AVR Temperature Sensor} | |||
| For starters I setup the code to read from the internal temp sensor on the duino. However there is also this: | |||
| https://thecavepearlproject.org/2019/02/25/no-parts-temperature-measurement-with-arduino-pro-mini-to-0-005c-or-better/ | |||
| This would be something to do for more resolution. The built in sensor is not very good, so this above link would be great. Hack a day also covers it. | |||
| \section{Wiring Pinout is wrong on Internet - Cable has labels} | |||
| I looked at the picture I have detailing the pinout (Delco Delphi radio wiring diagram.jpg in resources). It's close, but not 100\% correct. I found that the cable itself has small text labels on each wire which explain which everything does. I didn't notice earlier, as I didn't look close enough (and no one mentioned this). | |||
| \end{document} | |||
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| \documentclass[11pt]{article} | |||
| %Gummi|065|=) | |||
| \title{\textbf{Car Stereo Replacement}} | |||
| \author{Steak Electronics} | |||
| \date{10/27/19} | |||
| \begin{document} | |||
| \maketitle | |||
| \section{Overview} | |||
| Replacing a car stereo. | |||
| \section{Work Log} | |||
| \subsection{I2C OLED display} | |||
| Just for fun, I bought an I2C oled display and are going to use it to display something. Notes on this: | |||
| Using the adafruit SSD1306 and GFX library (this procedure is well covered in other places), you can load an example sketch and get it running. First thing to change is to remove the Adafruit logo and replace it with my own. Let's do that. | |||
| From https://design.goeszen.com/convert-image-for-oled-display.html | |||
| \begin{verbatim} | |||
| I'm on Linux here and found that the readily-available ImageMagick package will do the trick for you without any scripting. And runs on the CLI! Simple as that: | |||
| convert some_image.png some.image.mono | |||
| \end{verbatim} | |||
| That's efficient. But it didn't really work out. Too much work, I don't need it that bad. Have to convert it to something the c compiler can read. | |||
| \subsection{Internal AVR Temperature Sensor} | |||
| For starters I setup the code to read from the internal temp sensor on the duino. However there is also this: | |||
| https://thecavepearlproject.org/2019/02/25/no-parts-temperature-measurement-with-arduino-pro-mini-to-0-005c-or-better/ | |||
| This would be something to do for more resolution. The built in sensor is not very good, so this above link would be great. Hack a day also covers it. | |||
| \section{Wiring Pinout is wrong on Internet} | |||
| I looked at the picture I have detailing the pinout (Delco Delphi radio wiring diagram.jpg in resources). It's close, but not exact to the cable. I found that the cable has small text labels on each wire which explain which everything does. I didn't notice earlier, as I didn't look close enough (and no one mentioned this). | |||
| \end{document} | |||
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| \relax | |||
| \@writefile{toc}{\contentsline {section}{\numberline {1}Overview}{2}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {2}Chip Hunting}{2}} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {2.1}Gas Sensor Tuning}{2}} | |||
| \@writefile{lof}{\contentsline {figure}{\numberline {1}{\ignorespaces Application Note resistance table\relax }}{3}} | |||
| \@writefile{toc}{\contentsline {subsubsection}{\numberline {2.1.1}Fixed resistors}{3}} | |||
| \@writefile{toc}{\contentsline {subsubsection}{\numberline {2.1.2}Gas Sensor Power Usage}{3}} | |||
| \@writefile{toc}{\contentsline {subsubsection}{\numberline {2.1.3}PCB Layout}{3}} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {2.2}Switcher}{3}} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {2.3}Enclosure}{3}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {3}CAD Layout}{4}} | |||
| \@writefile{lof}{\contentsline {figure}{\numberline {2}{\ignorespaces Freecad has the ability to pull in boards from Kicad. Even without step file dependencies you can see how the PCB will fit a case\relax }}{4}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {4}PCB Assembly}{4}} | |||
| \citation{Schram} | |||
| \citation{Pickard} | |||
| \citation{EEVBlog} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {4.1}Place Sensors on the Floor}{5}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {5}In Consideration of ``Hazardous Locations''}{5}} | |||
| \citation{Fuchs} | |||
| \@writefile{toc}{\contentsline {subsection}{\numberline {5.1}What Class is my Company?}{6}} | |||
| \@writefile{toc}{\contentsline {subsubsection}{\numberline {5.1.1}Encapsulated Fuses}{6}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {6}Existing Gas Detectors}{6}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {7}Switching Power Supply}{7}} | |||
| \@writefile{lof}{\contentsline {figure}{\numberline {3}{\ignorespaces Prototype\relax }}{7}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {8}Connecting the Sensor by a Wire}{7}} | |||
| \bibcite{Schram}{1} | |||
| \@writefile{lof}{\contentsline {figure}{\numberline {4}{\ignorespaces A simple solution.\relax }}{8}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {9}Calibration}{8}} | |||
| \@writefile{toc}{\contentsline {section}{\numberline {10}References}{8}} | |||
| \bibcite{Pickard}{2} | |||
| \bibcite{EEVBlog}{3} | |||
| \bibcite{Fuchs}{4} | |||
| \bibcite{}{5} | |||
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| \documentclass[11pt]{article} | |||
| %Gummi|065|=) | |||
| \usepackage{graphicx} | |||
| \usepackage{caption} | |||
| \usepackage{xcolor} | |||
| \usepackage[vcentering,dvips]{geometry} | |||
| \geometry{papersize={6in,9in},total={4.5in,6.8in}} | |||
| \title{\textbf{Flammable Gas Sensor}} | |||
| \author{Steak Electronics} | |||
| \date{} | |||
| \begin{document} | |||
| \maketitle | |||
| \tableofcontents | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Overview}} | |||
| Shop needs a flammable gas sensor, for safety. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Chip Hunting}} | |||
| I'm looking at the following: | |||
| \begin{itemize} | |||
| \item SGAS711 | |||
| \item 200K fixed resistor | |||
| \item 1M potentiometer | |||
| \item Arduino Nano (for speed) | |||
| \item Ample Power Supply They are recommending 7 Volts for the heater. So, one rated for 1A. | |||
| \item led notifiers | |||
| \item Long cables to separate sensor from device. (optional) | |||
| \end{itemize} | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Gas Sensor Tuning}} | |||
| The flammable gas sensor has different sensitivities for different gases (see data sheet, Figure 8). I'm going to need to test for something specific, i.e. if the shop needs to watch out for acetone, I should test acetone. Of course, if enough of a flammable gas is in the air, it will set it off no matter what, but I should focus on what the danger is for calibrating. | |||
| Based on the resistance chart, I'm going to use a fixed 200K and a 1M pot. Pots are to be avoided, but here we need to calibrate over time. For the response of the v divider, the sensor is not linear, but closer (though not quite) logarithmic. So what I will do, is have to use some math on the micro, and use the formula they give in the Datasheet, to get a logarithmic output that appears linear (figure 5). For my needs, it is good enough. | |||
| \includegraphics[scale=0.8]{../pics/resistances.png} | |||
| \captionof{figure}{Application Note resistance table} | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{Fixed resistors}} | |||
| If these sensors are consistent enough, possibly I could use fixed resistors later. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{Gas Sensor Power Usage}} | |||
| Rated at 900mW for 7V, so about 150mA (128mA). I know from prior experience these things heat up, so we need plenty of power. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{PCB Layout}} | |||
| The gas sensor must be sideways, as there is excessive dust in the shop so, the holes will be on the side. I will do a 90 degree edge mount pcb. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Switcher}} | |||
| STS1024S6V5 Seems like a fair option for now. Output is 6.5 volts which is enough. Will use a module. Need to make a footprint. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Enclosure}} | |||
| We need a box that is tall enough to be a cube. Also want square, not rectangular. I plan to have the leds light from the back of the pcb. The pcb will be the top cover / front. The top cover / front will be the box, put on its side, so dust doesn't collect on the leds. Need a cube. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{CAD Layout}} | |||
| I found that Kicad step up in Freecad is helpful for making sure your board will fit the enclosure. A very helpful addition to an arsenal. Although I didn't test it until after rev 1. | |||
| \begin{center} | |||
| \includegraphics[scale=0.5]{../pics/kicadstepup1.jpg} | |||
| \captionof{figure}{Freecad has the ability to pull in boards from Kicad. Even without step file dependencies you can see how the PCB will fit a case} | |||
| \end{center} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{PCB Assembly}} | |||
| Most of the board came out ok. Power section is routed right. I need to move the barrel plug further out of the board, so it fits with the case better. The one issue I overlooked | |||
| was the A6, and A7 pins, which have no digital circuitry behind them. So I have some pins that can't light up. I'll have to bodge wires in, or respin the board. Simple fix. Oversight on my part, that's all. I assumed GPIO on all pins, but here are two analog pins that can't function as GPIO. | |||
| \vspace{0.2in} | |||
| I'll use D7, and D8. Looks like I also missed the wire from VSenseOut of the Gas sensor to the board. So that will go to A6. Technically, I missed a net on the schematic. | |||
| \vspace{0.2in} | |||
| One other fail of the enclosure, is that the Arduino nano won't fit with female pin headers holding it in. This means, instead of easily being socketable, I'll have to solder the board in. Not a deal-breaker, but I would prefer the nano to be easily removable. I don't like soldering it on the board. In the future, I need to find a taller enclosure. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Place Sensors on the Floor}} | |||
| Being that at least some flammable gases are heavier than air\footnote{Reference: Plumbing, Rex Cauldwell, 2006, page 137 - Gas Heater Awareness - Great book.}(in our case, they are, your situation may vary) it is logical for us to put them on the floor. There are no rules, though so why not both? It would be interesting to see the LEDs responding differently at say waist height, and at your feet. That would indicate different gas in the air. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{In Consideration of ``Hazardous Locations''}} | |||
| Up to this point, I have not paid any attention to official rules or standards regarding safety\footnote{Our environment is only dangerous when there is a gas leak (extremely rarely), so we are the least strict of the hazardous location types. In the US, this is Class 1, Division 2. Gas (class 1) can be present, but is not normally (division 2). We regularly have dust in our air, however it is silica and therefore inert / not explosive.}. The search term for a device like this that may be in an environment that can dangerous is \textbf{hazardous locations}. There are a few books on the subject I found (specifically for electronics in hazardous locations). I downloaded the PDF of a few online, but was not impressed with the writing quality enough to buy them with the exception of \emph{Electrical Installations in Hazardous Locations} by Peter Schram \cite{Schram}. There is also a succint Application note which covers a general overview in Linear Technology Magazine September 2009, also accessible online \cite{Pickard}. As a launchoff point, some discussion can also be found online in various forums \cite{EEVBlog}. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{What Class is my Company?}} | |||
| Based on \cite{Fuchs}, we are a Class 1, Division 2. With the Class 1, being Group D, as we would have leaks of those gases. It's possible that certain areas (inside the reactors for example) may be a higher class. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{Encapsulated Fuses}} | |||
| Encapsulated fuses are also referred to as UL913 online (e.g. in stores). UL913 is UL's \emph{Standard for Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, III, Division 1, Hazardous (Classified) Locations}. Another term to search for is \emph{intrinsically safe} on the parametric search for fuses. The cheapest intrinsically safe fuse in 1 quantity on Digikey is currently \$4.50. Ouch. Safety requirements sure help some people, just not the buyers. I see a market, for a blobbed fuse at \$1. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Existing Gas Detectors}} | |||
| We have already purchased a commercial gas detector. This particular model is designed so that the control box is kept separated from the sensor. The sensor has a 30 foot cable. The control box is installed in the ceiling. \footnote{See in the git: teardowns 2019, the RKI instruments combustible gas sensor.} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Switching Power Supply}} | |||
| In search of a low part count, simple to deploy switcher I came across this in my rss (https://hackaday.com/2019/08/11/switching-over-to-smps-for-efficiency/). The LM2576 is easy enough to use instead of a lm317, and requires only a diode and inductor more. Here I need more power efficiency from the 12V input so that should work. A simple go-to switcher. | |||
| \begin{center} | |||
| \includegraphics[scale=0.3]{../pics/DSCN2209.JPG} | |||
| \captionof{figure}{Prototype} | |||
| \end{center} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Connecting the Sensor by a Wire}} | |||
| Upon showing this to my family co. who wanted it, they mentioned they wanted a cable going to the sensor. I looked at the RKI Instruments flammable gas sensor, which we have a few of, and these used a 22 Gauge 4 conductor cable. That is \$50 for 100' of cable. A more DIY solution is to grab some 4 pair CAT5E or CAT6 and connect two wires to each screw terminal on the board. That is what I will do. Saves money, and should work no issue, up to the 30 feet max that I need. Any small box can be used for the sensors. I might build a pcb mount for those, or perhaps just some hot glue. Depends on what works the best, while being efficient. | |||
| \\ | |||
| \begin{center} | |||
| \includegraphics[scale=0.4]{../pics/DSCN2193.JPG} | |||
| \captionof{figure}{A simple solution.} | |||
| \end{center} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Calibration}} | |||
| This is the real task of this project. Making a gas sensor is easy, calibrating it, is another step. Thankfully, some companies sell calibration tanks. For calibration you might calibrate on the LEL or the lowest acceptable level before an alarm should be fired off for a given chemical. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{References}} | |||
| \begin{thebibliography}{99} | |||
| \bibitem{Schram} | |||
| Peter Schram, | |||
| \emph{Electrical Installations in Hazardous Locations}, first edition - 1991, National Fire Protection Association (NFPA), ISBN-13: 9780877653561. | |||
| \bibitem{Pickard} | |||
| Murphy Pickard, | |||
| \emph{Surge Stopper IC Simplifies Design of Intrinsic Safety Barrier for Electronics Destined for Hazardous Environments}, Linear Technology Magazine September 2009, https://www.analog.com/en/technical-articles/surge-stopper-ic-simplifies-design-of-intrinsic-safety-barrier-for-electronics.html . | |||
| \bibitem{EEVBlog} | |||
| Various, | |||
| \emph{Electronics Design for Explosive Envirionment}, EEVBlog Forums, https://www.eevblog.com/forum/chat/electronics-design-for-explosive-environment/?all, http://web.archive.org/web/20190410172437/http://www.eevblog.com/forum/chat/electronics-design-for-explosive-environment/?all. | |||
| \bibitem{Fuchs} | |||
| Various, | |||
| \emph{Explosion Protection and Intrinsic Safety 101}, Pepperl Fuchs, https://www.pepperl-fuchs.com/usa/downloads\_USA/explosion-protection-and-intrinsic-safety-101.pdf, http://web.archive.org/web/20190721221654/https://www.pepperl-fuchs.com/usa/downloads\_USA/explosion-protection-and-intrinsic-safety-101.pdf. | |||
| \bibitem{} | |||
| \end{thebibliography} | |||
| \end{document} | |||
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| \usepackage[vcentering,dvips]{geometry} | |||
| \geometry{papersize={6in,9in},total={4.5in,6.8in}} | |||
| \title{\textbf{Flammable Gas Sensor}} | |||
| \author{Steak Electronics} | |||
| \date{} | |||
| \begin{document} | |||
| \maketitle | |||
| \tableofcontents | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Overview}} | |||
| Shop needs a flammable gas sensor, for safety. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Chip Hunting}} | |||
| I'm looking at the following: | |||
| \begin{itemize} | |||
| \item SGAS711 | |||
| \item 200K fixed resistor | |||
| \item 1M potentiometer | |||
| \item Arduino Nano (for speed) | |||
| \item Ample Power Supply They are recommending 7 Volts for the heater. So, one rated for 1A. | |||
| \item led notifiers | |||
| \item Long cables to separate sensor from device. (optional) | |||
| \end{itemize} | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Gas Sensor Tuning}} | |||
| The flammable gas sensor has different sensitivities for different gases (see data sheet, Figure 8). I'm going to need to test for something specific, i.e. if the shop needs to watch out for acetone, I should test acetone. Of course, if enough of a flammable gas is in the air, it will set it off no matter what, but I should focus on what the danger is for calibrating. | |||
| Based on the resistance chart, I'm going to use a fixed 200K and a 1M pot. Pots are to be avoided, but here we need to calibrate over time. For the response of the v divider, the sensor is not linear, but closer (though not quite) logarithmic. So what I will do, is have to use some math on the micro, and use the formula they give in the Datasheet, to get a logarithmic output that appears linear (figure 5). For my needs, it is good enough. | |||
| \includegraphics[scale=0.8]{../pics/resistances.png} | |||
| \captionof{figure}{Application Note resistance table} | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{Fixed resistors}} | |||
| If these sensors are consistent enough, possibly I could use fixed resistors later. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{Gas Sensor Power Usage}} | |||
| Rated at 900mW for 7V, so about 150mA (128mA). I know from prior experience these things heat up, so we need plenty of power. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{PCB Layout}} | |||
| The gas sensor must be sideways, as there is excessive dust in the shop so, the holes will be on the side. I will do a 90 degree edge mount pcb. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Switcher}} | |||
| STS1024S6V5 Seems like a fair option for now. Output is 6.5 volts which is enough. Will use a module. Need to make a footprint. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Enclosure}} | |||
| We need a box that is tall enough to be a cube. Also want square, not rectangular. I plan to have the leds light from the back of the pcb. The pcb will be the top cover / front. The top cover / front will be the box, put on its side, so dust doesn't collect on the leds. Need a cube. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{CAD Layout}} | |||
| I found that Kicad step up in Freecad is helpful for making sure your board will fit the enclosure. A very helpful addition to an arsenal. Although I didn't test it until after rev 1. | |||
| \begin{center} | |||
| \includegraphics[scale=0.5]{../pics/kicadstepup1.jpg} | |||
| \captionof{figure}{Freecad has the ability to pull in boards from Kicad. Even without step file dependencies you can see how the PCB will fit a case} | |||
| \end{center} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{PCB Assembly}} | |||
| Most of the board came out ok. Power section is routed right. I need to move the barrel plug further out of the board, so it fits with the case better. The one issue I overlooked | |||
| was the A6, and A7 pins, which have no digital circuitry behind them. So I have some pins that can't light up. I'll have to bodge wires in, or respin the board. Simple fix. Oversight on my part, that's all. I assumed GPIO on all pins, but here are two analog pins that can't function as GPIO. | |||
| \vspace{0.2in} | |||
| I'll use D7, and D8. Looks like I also missed the wire from VSenseOut of the Gas sensor to the board. So that will go to A6. Technically, I missed a net on the schematic. | |||
| \vspace{0.2in} | |||
| One other fail of the enclosure, is that the Arduino nano won't fit with female pin headers holding it in. This means, instead of easily being socketable, I'll have to solder the board in. Not a deal-breaker, but I would prefer the nano to be easily removable. I don't like soldering it on the board. In the future, I need to find a taller enclosure. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{Place Sensors on the Floor}} | |||
| Being that at least some flammable gases are heavier than air\footnote{Reference: Plumbing, Rex Cauldwell, 2006, page 137 - Gas Heater Awareness - Great book.}(in our case, they are, your situation may vary) it is logical for us to put them on the floor. There are no rules, though so why not both? It would be interesting to see the LEDs responding differently at say waist height, and at your feet. That would indicate different gas in the air. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{In Consideration of ``Hazardous Locations''}} | |||
| Up to this point, I have not paid any attention to official rules or standards regarding safety\footnote{Our environment is only dangerous when there is a gas leak (extremely rarely), so we are the least strict of the hazardous location types. In the US, this is Class 1, Division 2. Gas (class 1) can be present, but is not normally (division 2). We regularly have dust in our air, however it is silica and therefore inert / not explosive.}. The search term for a device like this that may be in an environment that can dangerous is \textbf{hazardous locations}. There are a few books on the subject I found (specifically for electronics in hazardous locations). I downloaded the PDF of a few online, but was not impressed with the writing quality enough to buy them with the exception of \emph{Electrical Installations in Hazardous Locations} by Peter Schram \cite{Schram}. There is also a succint Application note which covers a general overview in Linear Technology Magazine September 2009, also accessible online \cite{Pickard}. As a launchoff point, some discussion can also be found online in various forums \cite{EEVBlog}. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsection{What Class is my Company?}} | |||
| Based on \cite{Fuchs}, we are a Class 1, Division 2. With the Class 1, being Group D, as we would have leaks of those gases. It's possible that certain areas (inside the reactors for example) may be a higher class. | |||
| \textcolor{green!60!blue!70}{ | |||
| \subsubsection{Encapsulated Fuses}} | |||
| Encapsulated fuses are also referred to as UL913 online (e.g. in stores). UL913 is UL's \emph{Standard for Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, III, Division 1, Hazardous (Classified) Locations}. Another term to search for is \emph{intrinsically safe} on the parametric search for fuses. The cheapest intrinsically safe fuse in 1 quantity on Digikey is currently \$4.50. Ouch. Safety requirements sure help some people, just not the buyers. I see a market, for a blobbed fuse at \$1. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Existing Gas Detectors}} | |||
| We have already purchased a commercial gas detector. This particular model is designed so that the control box is kept separated from the sensor. The sensor has a 30 foot cable. The control box is installed in the ceiling. \footnote{See in the git: teardowns 2019, the RKI instruments combustible gas sensor.} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Switching Power Supply}} | |||
| In search of a low part count, simple to deploy switcher I came across this in my rss (https://hackaday.com/2019/08/11/switching-over-to-smps-for-efficiency/). The LM2576 is easy enough to use instead of a lm317, and requires only a diode and inductor more. Here I need more power efficiency from the 12V input so that should work. A simple go-to switcher. | |||
| \begin{center} | |||
| \includegraphics[scale=0.3]{../pics/DSCN2209.JPG} | |||
| \captionof{figure}{Prototype} | |||
| \end{center} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Connecting the Sensor by a Wire}} | |||
| Upon showing this to my family co. who wanted it, they mentioned they wanted a cable going to the sensor. I looked at the RKI Instruments flammable gas sensor, which we have a few of, and these used a 22 Gauge 4 conductor cable. That is \$50 for 100' of cable. A more DIY solution is to grab some 4 pair CAT5E or CAT6 and connect two wires to each screw terminal on the board. That is what I will do. Saves money, and should work no issue, up to the 30 feet max that I need. Any small box can be used for the sensors. I might build a pcb mount for those, or perhaps just some hot glue. Depends on what works the best, while being efficient. | |||
| \begin{center} | |||
| \includegraphics[scale=0.3]{../pics/DSCN2193.JPG} | |||
| \captionof{figure}{A simple solution.} | |||
| \end{center} | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{Calibration}} | |||
| This is the real task of this project. Making a gas sensor is easy, calibrating it, is another step. Thankfully, some companies sell calibration tanks. For calibration you might calibrate on the LEL or the lowest acceptable level before an alarm should be fired off for a given chemical. | |||
| \textcolor{green!60!blue!70}{ | |||
| \section{References}} | |||
| \begin{thebibliography}{99} | |||
| \bibitem{Schram} | |||
| Peter Schram, | |||
| \emph{Electrical Installations in Hazardous Locations}, first edition - 1991, National Fire Protection Association (NFPA), ISBN-13: 9780877653561. | |||
| \bibitem{Pickard} | |||
| Murphy Pickard, | |||
| \emph{Surge Stopper IC Simplifies Design of Intrinsic Safety Barrier for Electronics Destined for Hazardous Environments}, Linear Technology Magazine September 2009, https://www.analog.com/en/technical-articles/surge-stopper-ic-simplifies-design-of-intrinsic-safety-barrier-for-electronics.html . | |||
| \bibitem{EEVBlog} | |||
| Various, | |||
| \emph{Electronics Design for Explosive Envirionment}, EEVBlog Forums, https://www.eevblog.com/forum/chat/electronics-design-for-explosive-environment/?all, http://web.archive.org/web/20190410172437/http://www.eevblog.com/forum/chat/electronics-design-for-explosive-environment/?all. | |||
| \bibitem{Fuchs} | |||
| Various, | |||
| \emph{Explosion Protection and Intrinsic Safety 101}, Pepperl Fuchs, https://www.pepperl-fuchs.com/usa/downloads\_USA/explosion-protection-and-intrinsic-safety-101.pdf, http://web.archive.org/web/20190721221654/https://www.pepperl-fuchs.com/usa/downloads\_USA/explosion-protection-and-intrinsic-safety-101.pdf. | |||
| \bibitem{} | |||
| \end{thebibliography} | |||
| \end{document} | |||
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| \contentsline {section}{\numberline {1}Overview}{2} | |||
| \contentsline {section}{\numberline {2}Chip Hunting}{2} | |||
| \contentsline {subsection}{\numberline {2.1}Gas Sensor Tuning}{2} | |||
| \contentsline {subsubsection}{\numberline {2.1.1}Fixed resistors}{3} | |||
| \contentsline {subsubsection}{\numberline {2.1.2}Gas Sensor Power Usage}{3} | |||
| \contentsline {subsubsection}{\numberline {2.1.3}PCB Layout}{3} | |||
| \contentsline {subsection}{\numberline {2.2}Switcher}{3} | |||
| \contentsline {subsection}{\numberline {2.3}Enclosure}{3} | |||
| \contentsline {section}{\numberline {3}CAD Layout}{4} | |||
| \contentsline {section}{\numberline {4}PCB Assembly}{4} | |||
| \contentsline {subsection}{\numberline {4.1}Place Sensors on the Floor}{5} | |||
| \contentsline {section}{\numberline {5}In Consideration of ``Hazardous Locations''}{5} | |||
| \contentsline {subsection}{\numberline {5.1}What Class is my Company?}{6} | |||
| \contentsline {subsubsection}{\numberline {5.1.1}Encapsulated Fuses}{6} | |||
| \contentsline {section}{\numberline {6}Existing Gas Detectors}{6} | |||
| \contentsline {section}{\numberline {7}Switching Power Supply}{7} | |||
| \contentsline {section}{\numberline {8}Connecting the Sensor by a Wire}{7} | |||
| \contentsline {section}{\numberline {9}Calibration}{8} | |||
| \contentsline {section}{\numberline {10}References}{8} | |||
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| \@writefile{toc}{\contentsline {subsection}{\numberline {4.1}Current usage, and Solar Project}{10}} | |||
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| \@writefile{toc}{\contentsline {section}{\numberline {5}Rev 2 Build}{11}} | |||
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| \documentclass[11pt]{article} | |||
| %Gummi|065|=) | |||
| \usepackage{graphicx} | |||
| \usepackage{caption} | |||
| \title{\textbf{BatteryMonitorBoard}} | |||
| \author{Steak Electronics} | |||
| \date{} | |||
| \begin{document} | |||
| \maketitle | |||
| \tableofcontents | |||
| \section{Overview} | |||
| \section{Chip Hunting} | |||
| Need to find a chip for battery charging. Some sheets have been saved. I looked at TI primarily. Though considered one AD/LTC. BQ2954 is out of the question as its too complex in its application circuit. THe BQ2000 is a 8 pin DIP and seems like a good start. That will cover nicad/nimh, and lithium batteries. | |||
| Though the BQ2000 is a bit of a mess as well. Data sheet has a complex circuit. There is a simpler one here: | |||
| http://www.ti.com/lit/pdf/sluu007 | |||
| and | |||
| https://electronics.stackexchange.com/questions/95970/how-to-use-battery-charge-controller-bq2002n | |||
| Regardless of the contents of that post, the fact is, the chip requires a lot of stuff. | |||
| https://www.st.com/content/ccc/resource/technical/document/datasheet/df/b9/e6/5b/ec/92/45/ed/CD00132951.pdf/files/CD00132951.pdf/jcr:content/translations/en.CD00132951.pdf | |||
| This chip: stc4054, is extremely simple. Limited to 1 lithium cell (so only 4.2 volts max) but application circuit is lean, and it has a shutdown pin, so you can turn off the charger. Price is the cheapest as well, at 1.50 for 1. | |||
| That looks hopeful. Why not multiple? | |||
| Need to remember to be careful of 4.1 lithium batteries. Most chargers are 4.2, and its easy to forget that there is a difference. | |||
| MCP73826 is another reasonable option. Slightly more complex, but not by much. | |||
| RT9526A is also simple. Let's start with the st chip. | |||
| Looks like the voltage on that pin should be between 1.2 and 2.4 in order to turn it off. Below 1.2 it is on, and monitoring current. Above 1.2 but below 2.4 it is off. above 2.4 it's putting 35ua into the battery. I think. | |||
| Also like the LTC1734, which is lithium / nicad. But expensive at 3-4 dollars. Don't see any lead acid battery chargers on digi that aren't being obsoleted. There's not one. I did see some on manufacturer's pages though. Just not here. | |||
| There is one microchip one (lead acid) based on a pic. App circuit is complex. | |||
| AN1015 is the app note. | |||
| So need a lead, and nicd charger still. | |||
| Tomorrow I'd like to look at maxim. I see this: | |||
| https://www.maximintegrated.com/en/products/power/battery-management/MAX1772.html | |||
| But the application circuit is too much for what I want to deal with. | |||
| Seems lead acid battery chargers are not as common as they must've been before. | |||
| Onsemi is only lithium batteries. | |||
| Mouser has only universal chargers, no lead. But universal includes lead. | |||
| let's check linear. LT1510 is an 8 pin simple device. Though it's nicad and lithium only. It says it can do lead in table, but not in datasheet. | |||
| lt1510 would work for nicad. data sheet figure 6 has a circuit for nicad. | |||
| What about lead? | |||
| lt1513 does the three main types: nicd,li-ion,lead | |||
| At a cost of \$10. | |||
| At digi, the bq2031 is the only lead battery chip (not multi type) that is in production. Not much choice. EDIT: actually that is not | |||
| recommended for new designs either. | |||
| http://www.eevblog.com/forum/beginners/mc34063-battery-charger/msg1378671/\#msg1378671 | |||
| Here he uses a boost regulator to power a battery. Essentially just setting the voltage. | |||
| http://www.eevblog.com/forum/projects/switching-lead-acid-battery-charger-ic/msg806972/\#msg806972 | |||
| Here is some better advice. | |||
| quote: | |||
| \begin{verbatim} | |||
| I'd recommend just float charging. It takes only a little longer | |||
| and is easier on the batteries. You will need to limit the initial | |||
| charge current to about 0.1 C (so 2 A for a 20 AH battery). The | |||
| easiest way to do this is a constant current/ constant voltage | |||
| power supply. Set the current limit to the desired charge current, | |||
| and the voltage to the float voltage (13.8 V adjusted for | |||
| temperature if needed). The voltage on the battery will slowly | |||
| increase over time until it reaches ~13.8 V, then the current will | |||
| slowly drop over time until it reaches nearly zero. At that point, | |||
| the battery is fully charged and you can either remove the charger | |||
| or just leave it on. | |||
| \end{verbatim} | |||
| Which is what I did with my solar battery charger, and it worked well. So I suppose there is no need for anything more than a vreg for lead batteries. This time I will go to the recommended 13.8 instead of what I had before (around 12) and I will do the same trickle charge method. Simple. Done. | |||
| May use 1512 instead. \$5 in 150 quantity. Hm... | |||
| \$10 in single. | |||
| That would cover lead, nicad. | |||
| Will need jumpers on R1 and R2 depending on what battery type. According to data sheet, li-ion the divider is a float voltage. In nicd, it is a top limit. | |||
| OK, i've decided: | |||
| \subsection{Part Selection Summary} | |||
| LT1512, and STC4054. | |||
| For starters, I will use stc as lithium and lt as nicad / lead. | |||
| this will avoid the worry of jumpers, and what not. Later I can be flexible. | |||
| Now onto other parts. I need some way to monitor the current, and of course a voltage tap. | |||
| Where to put current sense? I think before the battery. | |||
| I should put some jumpers in, so I can isolate everything though. I dont' want to mix circuits at the start. So isolate the charger from the op amp and sense, at first. | |||
| Let's go with the basic differential op amp in microchip an1332. I need a vreg supply (linear) at 15.5 volts, for the op amp, so it's above the lead battery voltage. Simplest two switchers I see are lm2577 or the mk3608. The mk is easier to use. | |||
| With that we have: | |||
| \begin{itemize} | |||
| \item Battery charger x 2 | |||
| \item voltage monitor x 2 | |||
| \item current monitor x 2 | |||
| \item ethernet (using off the shelf enc modules for now, but maybe | |||
| on board later). | |||
| \item microcontroller (nano) | |||
| \item temperature monitor (something like max6675 looks nice. can put on board, without difficulty). | |||
| \item additional taps into adc, and some op amps and current shunts not populated to be used as extra current - voltage converters. At least two. Put on modular schematic. | |||
| \end{itemize} | |||
| I also want a general current and voltage monitor. I want | |||
| to be able to watch the load on a battery, and record that as well... | |||
| Perhaps that will be separate. I might want to grab some off the shelf | |||
| current / voltage monitoring stuff, or just throw a few op amps with breakouts on the board. | |||
| Let's build. | |||
| Keep all schematics modular! | |||
| \textbf{A note on lt1512 tuning} | |||
| \begin{verbatim} | |||
| How this is tuned: | |||
| The V divider on Feedback pin | |||
| determines float voltage. | |||
| The R downstream of I_feedback | |||
| (after 24 ohm resistor) | |||
| determines current (100mV / R) | |||
| See data sheet for more details. | |||
| Put Simply: Set float voltage on r divider | |||
| and make sure current resistor is high enough | |||
| to be low current. | |||
| \end{verbatim} | |||
| \textbf{Calculating LT1512 vdivider} | |||
| \begin{verbatim} | |||
| Example calculation for R1: | |||
| R1 = (R2(Vbat - 1.245) )\ (1.245+R2(0.3uA)) | |||
| with default R2 at 12,400 | |||
| Desired Vbat float of 13.8 (lead) | |||
| (13.8 - 1.245) * 12400 == 155682 | |||
| 1.245 + (12400 * .000003) == .03720 + 1.245 == 1.2822 | |||
| 155682/1.2822 == 121417 | |||
| It would be evil for them to put 0.3uA and | |||
| expect you to convert that to 0.000003A | |||
| But that's what they did. At least they | |||
| give an example to check. | |||
| Five zeros on that. | |||
| \end{verbatim} | |||
| Based on the vdivider, what you are seeing is for high voltages, with R2 being the recommended 12.4K, is R1 150K at ~13, R1 220K at ~9V. | |||
| Some more notes | |||
| \begin{verbatim} | |||
| checking the given example: | |||
| 41200 * (8.2 - 1.245) 286546 | |||
| 41200 * 0.000003 + 1.245 == 1.3605 | |||
| lowest possible value (1.3V charge) | |||
| (1.3 - 1.245 ) * 12400 == 682 | |||
| (12400 * .000003 ) + 1.245 == 1.28 | |||
| 682 / 1.28 == 532 | |||
| so lowest resistor value must be 500 about... | |||
| \end{verbatim} | |||
| Lowest resistor would be 536. (e48 resistor) | |||
| \subsection{Current monitor} | |||
| I considered doing an (high side) op amp with external resistors per AN1322 microchip app note, but decided to go instead with a current monitor, ala ina169. There are a number of INA chips being advertised. Adafruit, for example sells the INA219 and there are many articles | |||
| about other current sense in the same family. There is the shunt | |||
| resistor value, and the gain resistor to set. I will use based off of the adafruit example, as well as the ti example a 1ohm shunt (for up to 1A readings, seems as you decrease the shunt you get more capacity in amperage to read), with a 1K gain resistor, which TI gives as an example in a table. That means voltage will equal current. | |||
| For the inductor | |||
| see lt data sheet for details. | |||
| must not be series resistance greater than 0.1 ohms. | |||
| \subsection{PCB Revision - Modular Parts} | |||
| I decided to route out some of the pcb, so I can possibly reuse the temperature sensor and perhaps the lithium battery charger. This was on revision 2. I got the first revision already made after a marathon one Sunday morning from 8-2pm. Here's how it is routed out. | |||
| \includegraphics{../pics/modular_reusable.jpg} | |||
| \captionof{figure}{Cut out with pliers and reuse parts.} | |||
| \subsubsection{Ripped off by temperature sensors} | |||
| The community around Arduino advertises the LM35, advertises the MAX6675. The latter is \$10 in one off quantity (\$5 from ebay), the former isn't cheap either, at \$2.00 about. Though the LM35 has a much more limited range. The LM35 is great as it's extremely simple to use (power and read voltage which converts directly to temperature). | |||
| I'll have to find an alternative for the MAX6675. At \$10 it's just stupid. A micro can do temperature as well. Maybe \$5 would be acceptable, but \$10 is not. How big are your pockets? | |||
| \vspace{0.4in} | |||
| \includegraphics[scale=0.3]{../pics/tinythermocouple.jpg} | |||
| \captionof{figure}{technoblogy has an article on using a micro with an external thermocouple} | |||
| Cheapest thermocouple on Digikey, is a digilent (they just import) thermocouple at \$10. Next is a DFRobot (chinese adafruit) at \$30 with a module included. Thermocouples are not cheap! Onto ebay.\footnote{Thermocouples: I forgot how they work today. I've read of them before but haven't used them much (have seen them in toasters. Now that I know they are worth \$5-10 I'm going to start retrieving them from broken toasters). When two dissimilar metals are put together, and then the metals are heated, you can get a voltage across them. This voltage can be read with an ADC. This phenomenon has a name, but the name is not important. Names just add another thing you need to remember. Bad idea. (OK, I remembered it, now I can fool myself into feeling intelligent - seebeck effect. Now let me go count my hertz, and volts, and teslas...) Wikipedia calls it the thermoelectric effect.} | |||
| After some research I decided to go with the Digilent probe. The cheapest used probe on ebay is \$10. I don't want the new ones from US, which is only \$5 cheaper. | |||
| \section{Bom Notes} | |||
| I should try to get rid of some expensive items where possible. | |||
| \vspace{0.2in} | |||
| tantalum is \$1. Try a ceramic. | |||
| MAX6675 is \$10. | |||
| Slide pot is just for fun. That can be removed. | |||
| \vspace{0.2in} | |||
| On the subject of boms, I have made two. The LT portion is complex, and requires its own bom. The rest of the items are on a different bom. I keep some things in stock so a few items have been omitted. | |||
| \subsection{SOD323 (diode) is equal to 0805} | |||
| Looks like the SOD323, diode / SC-73 package is near the 0805 package in size. SOD323 is slightly smaller, but not by much. They are probably interchangeable in practice. | |||
| \section{PCB Build and Test Notes} | |||
| I built the PCB. There were a few errors which I've put in the TODO file, but nothing show stopping. There will be a rev2 pcb. A few notes: | |||
| On the LT1512, if you float the voltage divider, and Feedback pin, the device will short out. My power supply continually is saving me on this. | |||
| For the voltage divider, you don't actually see the float voltage, between R1, and R2 of the divider, I don't think. The voltage, however does rise, above the divider, where the Vsw pin is. What you do see is the 1.24 reference, or some voltage near it. | |||
| What I'm seeing now, is if you connect a scope probe to the lt charge pin, (pin which charges the battery) you can adjust the divider and see the voltage rise. That must be the float voltage. Meanwhile, the feedback pin, which is downstream of the charge pin, has always about 1.24 or so. | |||
| So seems to work well. For a while, I misunderstood how the voltage divider was supposed to work, and spent a few hours double checking the divider values. I had wired the switches wrong in rev 1, but that was not the issue. The issue was my expectation to see the voltage between the divider actually be the float voltage, when that float voltage was above the divider. Must be some transistor math doing a calculation on the voltage divider. | |||
| With the 0.2 ohm resistor (in typical application first page of LT1512 data sheet), I had changed it to a 1ohm. That was still not enough, and I instead substituted in a 10ohm. This limits charging to 10mA. The 1 ohm resistor seemed to have some issue of high float voltages causing thermal runway... Maybe a 5 ohm resistor can be used for 20mA charging. This was only on high float voltages. With the 1 Nicd, I was able to do 80-100mA of charging, without issue. But once float is around 5-6 volts you start to get issues with the current growing exponentially from the main PSU, and the LT1512 chip overheating. (At \$8 each, a melted chip is to be avoided). | |||
| \subsection{Current usage, and Solar Project} | |||
| This project is a descendant of the solar battery charger project. I'm going to restart that project with some of these components, but might use the LT1372, or some other more efficient regulator. No current limiting should be necessary, given that I will use small solar panels (though current limit, might need to be in consideration). | |||
| The INA169 draws about 90uA when measuring the 10mA of current going through for a 6V lead battery. | |||
| \subsection{Current Limiting resistor on LT1512} | |||
| The Resistor after I Feedback, R10 (in my schematic. it's the 0.2 ohm resistor in the official data sheet)... In the circuit here, it is 1 ohm. It | |||
| will allow about 80mA into a NiCd at 1.2 | |||
| volts. At this level, there is an issue with | |||
| charging voltages above single cell lithium values. What happens | |||
| is that the circuit starts using over an amp of current and | |||
| the LT chip overheats. | |||
| If you increase the resistance, you | |||
| can lower the current output and thus also charge 6-12v | |||
| batteries. | |||
| Test with a current limiting power supply! | |||
| \subsection{Separate Grounds 1512} | |||
| I did not separate the grounds on the first run, and while there might be more noise (I didn't measure) everything seems to work, regardless. | |||
| \subsection{Switches Max Current} | |||
| These switches have a max current of 300mA. | |||
| \subsection{Usage} | |||
| Here's how to use this device. Plug in a 9-12V PSU. Connect USB to computer (bbb, rpi preferred for long term usage). | |||
| Measure the voltage divider. This value is found after the large diode, but before the voltage divider. Adjust the switches, and pot as needed. Check with a DMM, for the voltage - that will be the final charge voltage. | |||
| Connect battery + into INA169 (high side current sense) . Connect INA169 v out into LT CONN (which is same as where float voltage is measured). | |||
| Connect battery - into ground. Check ina169 ADC reading with Serial out or DMM, it should reflect the charging. You can also put a DMM in series with battery to confirm its charging. | |||
| \subsection{Forgot V Dividers for batteries gt 5v} | |||
| I guess I forgot a voltage divider on this board. I'll need at least 2 or 3 pins on the ADC to be 10\%, so that I can measure 6 and 12v lead batteries. Hmph. For rev 2 I guess. | |||
| \section{Rev 2 Build} | |||
| The board tends to slowly ramp up, pulling 150 at start, then moving eventually to 500mA (testing at fuse) before cutting back to about 400mA, and the 5V output has a bit of switching on it (thermal shutdown, possibly). It also heats up both the LT and the LM317 at this point. | |||
| I recall having this problem with the first board though I was able to get it working, after breaking some traces. On this board, occasionally, I was able to see it pull 60mA, and the output voltage became high. Otherwise the LT FB (I call it the LT Float voltage) became what was expected. But when it was 500mA (shorting?), the float V is low. More research needed. It's possible the LT chip has been damaged too much. The scope is quite clear on what is going on, though. And I was getting output voltages earlier with/without overheating. This is without a battery connected, though a battery added does not make a difference. | |||
| I hear a snap when its turning on sometimes. | |||
| \end{document} | |||
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| \documentclass[11pt]{article} | |||
| %Gummi|065|=) | |||
| \usepackage{graphicx} | |||
| \usepackage{caption} | |||
| \title{\textbf{BatteryMonitorBoard}} | |||
| \author{Steak Electronics} | |||
| \date{} | |||
| \begin{document} | |||
| \maketitle | |||
| \tableofcontents | |||
| \section{Overview} | |||
| \section{Chip Hunting} | |||
| Need to find a chip for battery charging. Some sheets have been saved. I looked at TI primarily. Though considered one AD/LTC. BQ2954 is out of the question as its too complex in its application circuit. THe BQ2000 is a 8 pin DIP and seems like a good start. That will cover nicad/nimh, and lithium batteries. | |||
| Though the BQ2000 is a bit of a mess as well. Data sheet has a complex circuit. There is a simpler one here: | |||
| http://www.ti.com/lit/pdf/sluu007 | |||
| and | |||
| https://electronics.stackexchange.com/questions/95970/how-to-use-battery-charge-controller-bq2002n | |||
| Regardless of the contents of that post, the fact is, the chip requires a lot of stuff. | |||
| https://www.st.com/content/ccc/resource/technical/document/datasheet/df/b9/e6/5b/ec/92/45/ed/CD00132951.pdf/files/CD00132951.pdf/jcr:content/translations/en.CD00132951.pdf | |||
| This chip: stc4054, is extremely simple. Limited to 1 lithium cell (so only 4.2 volts max) but application circuit is lean, and it has a shutdown pin, so you can turn off the charger. Price is the cheapest as well, at 1.50 for 1. | |||
| That looks hopeful. Why not multiple? | |||
| Need to remember to be careful of 4.1 lithium batteries. Most chargers are 4.2, and its easy to forget that there is a difference. | |||
| MCP73826 is another reasonable option. Slightly more complex, but not by much. | |||
| RT9526A is also simple. Let's start with the st chip. | |||
| Looks like the voltage on that pin should be between 1.2 and 2.4 in order to turn it off. Below 1.2 it is on, and monitoring current. Above 1.2 but below 2.4 it is off. above 2.4 it's putting 35ua into the battery. I think. | |||
| Also like the LTC1734, which is lithium / nicad. But expensive at 3-4 dollars. Don't see any lead acid battery chargers on digi that aren't being obsoleted. There's not one. I did see some on manufacturer's pages though. Just not here. | |||
| There is one microchip one (lead acid) based on a pic. App circuit is complex. | |||
| AN1015 is the app note. | |||
| So need a lead, and nicd charger still. | |||
| Tomorrow I'd like to look at maxim. I see this: | |||
| https://www.maximintegrated.com/en/products/power/battery-management/MAX1772.html | |||
| But the application circuit is too much for what I want to deal with. | |||
| Seems lead acid battery chargers are not as common as they must've been before. | |||
| Onsemi is only lithium batteries. | |||
| Mouser has only universal chargers, no lead. But universal includes lead. | |||
| let's check linear. LT1510 is an 8 pin simple device. Though it's nicad and lithium only. It says it can do lead in table, but not in datasheet. | |||
| lt1510 would work for nicad. data sheet figure 6 has a circuit for nicad. | |||
| What about lead? | |||
| lt1513 does the three main types: nicd,li-ion,lead | |||
| At a cost of \$10. | |||
| At digi, the bq2031 is the only lead battery chip (not multi type) that is in production. Not much choice. EDIT: actually that is not | |||
| recommended for new designs either. | |||
| http://www.eevblog.com/forum/beginners/mc34063-battery-charger/msg1378671/\#msg1378671 | |||
| Here he uses a boost regulator to power a battery. Essentially just setting the voltage. | |||
| http://www.eevblog.com/forum/projects/switching-lead-acid-battery-charger-ic/msg806972/\#msg806972 | |||
| Here is some better advice. | |||
| quote: | |||
| \begin{verbatim} | |||
| I'd recommend just float charging. It takes only a little longer | |||
| and is easier on the batteries. You will need to limit the initial | |||
| charge current to about 0.1 C (so 2 A for a 20 AH battery). The | |||
| easiest way to do this is a constant current/ constant voltage | |||
| power supply. Set the current limit to the desired charge current, | |||
| and the voltage to the float voltage (13.8 V adjusted for | |||
| temperature if needed). The voltage on the battery will slowly | |||
| increase over time until it reaches ~13.8 V, then the current will | |||
| slowly drop over time until it reaches nearly zero. At that point, | |||
| the battery is fully charged and you can either remove the charger | |||
| or just leave it on. | |||
| \end{verbatim} | |||
| Which is what I did with my solar battery charger, and it worked well. So I suppose there is no need for anything more than a vreg for lead batteries. This time I will go to the recommended 13.8 instead of what I had before (around 12) and I will do the same trickle charge method. Simple. Done. | |||
| May use 1512 instead. \$5 in 150 quantity. Hm... | |||
| \$10 in single. | |||
| That would cover lead, nicad. | |||
| Will need jumpers on R1 and R2 depending on what battery type. According to data sheet, li-ion the divider is a float voltage. In nicd, it is a top limit. | |||
| OK, i've decided: | |||
| \subsection{Part Selection Summary} | |||
| LT1512, and STC4054. | |||
| For starters, I will use stc as lithium and lt as nicad / lead. | |||
| this will avoid the worry of jumpers, and what not. Later I can be flexible. | |||
| Now onto other parts. I need some way to monitor the current, and of course a voltage tap. | |||
| Where to put current sense? I think before the battery. | |||
| I should put some jumpers in, so I can isolate everything though. I dont' want to mix circuits at the start. So isolate the charger from the op amp and sense, at first. | |||
| Let's go with the basic differential op amp in microchip an1332. I need a vreg supply (linear) at 15.5 volts, for the op amp, so it's above the lead battery voltage. Simplest two switchers I see are lm2577 or the mk3608. The mk is easier to use. | |||
| With that we have: | |||
| \begin{itemize} | |||
| \item Battery charger x 2 | |||
| \item voltage monitor x 2 | |||
| \item current monitor x 2 | |||
| \item ethernet (using off the shelf enc modules for now, but maybe | |||
| on board later). | |||
| \item microcontroller (nano) | |||
| \item temperature monitor (something like max6675 looks nice. can put on board, without difficulty). | |||
| \item additional taps into adc, and some op amps and current shunts not populated to be used as extra current - voltage converters. At least two. Put on modular schematic. | |||
| \end{itemize} | |||
| I also want a general current and voltage monitor. I want | |||
| to be able to watch the load on a battery, and record that as well... | |||
| Perhaps that will be separate. I might want to grab some off the shelf | |||
| current / voltage monitoring stuff, or just throw a few op amps with breakouts on the board. | |||
| Let's build. | |||
| Keep all schematics modular! | |||
| \textbf{A note on lt1512 tuning} | |||
| \begin{verbatim} | |||
| How this is tuned: | |||
| The V divider on Feedback pin | |||
| determines float voltage. | |||
| The R downstream of I_feedback | |||
| (after 24 ohm resistor) | |||
| determines current (100mV / R) | |||
| See data sheet for more details. | |||
| Put Simply: Set float voltage on r divider | |||
| and make sure current resistor is high enough | |||
| to be low current. | |||
| \end{verbatim} | |||
| \textbf{Calculating LT1512 vdivider} | |||
| \begin{verbatim} | |||
| Example calculation for R1: | |||
| R1 = (R2(Vbat - 1.245) )\ (1.245+R2(0.3uA)) | |||
| with default R2 at 12,400 | |||
| Desired Vbat float of 13.8 (lead) | |||
| (13.8 - 1.245) * 12400 == 155682 | |||
| 1.245 + (12400 * .000003) == .03720 + 1.245 == 1.2822 | |||
| 155682/1.2822 == 121417 | |||
| It would be evil for them to put 0.3uA and | |||
| expect you to convert that to 0.000003A | |||
| But that's what they did. At least they | |||
| give an example to check. | |||
| Five zeros on that. | |||
| \end{verbatim} | |||
| Based on the vdivider, what you are seeing is for high voltages, with R2 being the recommended 12.4K, is R1 150K at ~13, R1 220K at ~9V. | |||
| Some more notes | |||
| \begin{verbatim} | |||
| checking the given example: | |||
| 41200 * (8.2 - 1.245) 286546 | |||
| 41200 * 0.000003 + 1.245 == 1.3605 | |||
| lowest possible value (1.3V charge) | |||
| (1.3 - 1.245 ) * 12400 == 682 | |||
| (12400 * .000003 ) + 1.245 == 1.28 | |||
| 682 / 1.28 == 532 | |||
| so lowest resistor value must be 500 about... | |||
| \end{verbatim} | |||
| Lowest resistor would be 536. (e48 resistor) | |||
| \subsection{Current monitor} | |||
| I considered doing an (high side) op amp with external resistors per AN1322 microchip app note, but decided to go instead with a current monitor, ala ina169. There are a number of INA chips being advertised. Adafruit, for example sells the INA219 and there are many articles | |||
| about other current sense in the same family. There is the shunt | |||
| resistor value, and the gain resistor to set. I will use based off of the adafruit example, as well as the ti example a 1ohm shunt (for up to 1A readings, seems as you decrease the shunt you get more capacity in amperage to read), with a 1K gain resistor, which TI gives as an example in a table. That means voltage will equal current. | |||
| For the inductor | |||
| see lt data sheet for details. | |||
| must not be series resistance greater than 0.1 ohms. | |||
| \subsection{PCB Revision - Modular Parts} | |||
| I decided to route out some of the pcb, so I can possibly reuse the temperature sensor and perhaps the lithium battery charger. This was on revision 2. I got the first revision already made after a marathon one Sunday morning from 8-2pm. Here's how it is routed out. | |||
| \includegraphics{../pics/modular_reusable.jpg} | |||
| \captionof{figure}{Cut out with pliers and reuse parts.} | |||
| \subsubsection{Ripped off by temperature sensors} | |||
| The community around Arduino advertises the LM35, advertises the MAX6675. The latter is \$10 in one off quantity (\$5 from ebay), the former isn't cheap either, at \$2.00 about. Though the LM35 has a much more limited range. The LM35 is great as it's extremely simple to use (power and read voltage which converts directly to temperature). | |||
| I'll have to find an alternative for the MAX6675. At \$10 it's just stupid. A micro can do temperature as well. Maybe \$5 would be acceptable, but \$10 is not. How big are your pockets? | |||
| \vspace{0.4in} | |||
| \includegraphics[scale=0.3]{../pics/tinythermocouple.jpg} | |||
| \captionof{figure}{technoblogy has an article on using a micro with an external thermocouple} | |||
| Cheapest thermocouple on Digikey, is a digilent (they just import) thermocouple at \$10. Next is a DFRobot (chinese adafruit) at \$30 with a module included. Thermocouples are not cheap! Onto ebay.\footnote{Thermocouples: I forgot how they work today. I've read of them before but haven't used them much (have seen them in toasters. Now that I know they are worth \$5-10 I'm going to start retrieving them from broken toasters). When two dissimilar metals are put together, and then the metals are heated, you can get a voltage across them. This voltage can be read with an ADC. This phenomenon has a name, but the name is not important. Names just add another thing you need to remember. Bad idea. (OK, I remembered it, now I can fool myself into feeling intelligent - seebeck effect. Now let me go count my hertz, and volts, and teslas...) Wikipedia calls it the thermoelectric effect.} | |||
| After some research I decided to go with the Digilent probe. The cheapest used probe on ebay is \$10. I don't want the new ones from US, which is only \$5 cheaper. | |||
| \section{Bom Notes} | |||
| I should try to get rid of some expensive items where possible. | |||
| \vspace{0.2in} | |||
| tantalum is \$1. Try a ceramic. | |||
| MAX6675 is \$10. | |||
| Slide pot is just for fun. That can be removed. | |||
| \vspace{0.2in} | |||
| On the subject of boms, I have made two. The LT portion is complex, and requires its own bom. The rest of the items are on a different bom. I keep some things in stock so a few items have been omitted. | |||
| \subsection{SOD323 (diode) is equal to 0805} | |||
| Looks like the SOD323, diode / SC-73 package is near the 0805 package in size. SOD323 is slightly smaller, but not by much. They are probably interchangeable in practice. | |||
| \section{PCB Build and Test Notes} | |||
| I built the PCB. There were a few errors which I've put in the TODO file, but nothing show stopping. There will be a rev2 pcb. A few notes: | |||
| On the LT1512, if you float the voltage divider, and Feedback pin, the device will short out. My power supply continually is saving me on this. | |||
| For the voltage divider, you don't actually see the float voltage, between R1, and R2 of the divider, I don't think. The voltage, however does rise, above the divider, where the Vsw pin is. What you do see is the 1.24 reference, or some voltage near it. | |||
| What I'm seeing now, is if you connect a scope probe to the lt charge pin, (pin which charges the battery) you can adjust the divider and see the voltage rise. That must be the float voltage. Meanwhile, the feedback pin, which is downstream of the charge pin, has always about 1.24 or so. | |||
| So seems to work well. For a while, I misunderstood how the voltage divider was supposed to work, and spent a few hours double checking the divider values. I had wired the switches wrong in rev 1, but that was not the issue. The issue was my expectation to see the voltage between the divider actually be the float voltage, when that float voltage was above the divider. Must be some transistor math doing a calculation on the voltage divider. | |||
| With the 0.2 ohm resistor (in typical application first page of LT1512 data sheet), I had changed it to a 1ohm. That was still not enough, and I instead substituted in a 10ohm. This limits charging to 10mA. The 1 ohm resistor seemed to have some issue of high float voltages causing thermal runway... Maybe a 5 ohm resistor can be used for 20mA charging. This was only on high float voltages. With the 1 Nicd, I was able to do 80-100mA of charging, without issue. But once float is around 5-6 volts you start to get issues with the current growing exponentially from the main PSU, and the LT1512 chip overheating. (At \$8 each, a melted chip is to be avoided). | |||
| \subsection{Current usage, and Solar Project} | |||
| This project is a descendant of the solar battery charger project. I'm going to restart that project with some of these components, but might use the LT1372, or some other more efficient regulator. No current limiting should be necessary, given that I will use small solar panels (though current limit, might need to be in consideration). | |||
| The INA169 draws about 90uA when measuring the 10mA of current going through for a 6V lead battery. | |||
| \subsection{Current Limiting resistor on LT1512} | |||
| The Resistor after I Feedback, R10 (in my schematic. it's the 0.2 ohm resistor in the official data sheet)... In the circuit here, it is 1 ohm. It | |||
| will allow about 80mA into a NiCd at 1.2 | |||
| volts. At this level, there is an issue with | |||
| charging voltages above single cell lithium values. What happens | |||
| is that the circuit starts using over an amp of current and | |||
| the LT chip overheats. | |||
| If you increase the resistance, you | |||
| can lower the current output and thus also charge 6-12v | |||
| batteries. | |||
| Test with a current limiting power supply! | |||
| \subsection{Separate Grounds 1512} | |||
| I did not separate the grounds on the first run, and while there might be more noise (I didn't measure) everything seems to work, regardless. | |||
| \subsection{Switches Max Current} | |||
| These switches have a max current of 300mA. | |||
| \subsection{Usage} | |||
| Here's how to use this device. Plug in a 9-12V PSU. Connect USB to computer (bbb, rpi preferred for long term usage). | |||
| Measure the voltage divider. This value is found after the large diode, but before the voltage divider. Adjust the switches, and pot as needed. Check with a DMM, for the voltage - that will be the final charge voltage. | |||
| Connect battery + into INA169 (high side current sense) . Connect INA169 v out into LT CONN (which is same as where float voltage is measured). | |||
| Connect battery - into ground. Check ina169 ADC reading with Serial out or DMM, it should reflect the charging. You can also put a DMM in series with battery to confirm its charging. | |||
| \subsection{Forgot V Dividers for batteries gt 5v} | |||
| I guess I forgot a voltage divider on this board. I'll need at least 2 or 3 pins on the ADC to be 10\%, so that I can measure 6 and 12v lead batteries. Hmph. For rev 2 I guess. | |||
| \section{Rev 2 Build} | |||
| The board tends to slowly ramp up, pulling 150 at start, then moving eventually to 500mA (testing at fuse) before cutting back to about 400mA, and the 5V output has a bit of switching on it (thermal shutdown, possibly). It also heats up both the LT and the LM317 at this point. | |||
| I recall having this problem with the first board though I was able to get it working, after breaking some traces. On this board, occasionally, I was able to see it pull 60mA, and the output voltage became high. Otherwise the LT FB (I call it the LT Float voltage) became what was expected. More research needed. It's possible the LT chip has been damaged too much. The scope is quite clear on what is going on, though. And I was getting output voltages earlier with/without overheating. This is without a battery connected, though a battery added does not make a difference. | |||
| \end{document} | |||
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| \contentsline {section}{\numberline {1}Overview}{1} | |||
| \contentsline {section}{\numberline {2}Chip Hunting}{1} | |||
| \contentsline {subsection}{\numberline {2.1}Part Selection Summary}{3} | |||
| \contentsline {subsection}{\numberline {2.2}Current monitor}{5} | |||
| \contentsline {subsection}{\numberline {2.3}PCB Revision - Modular Parts}{6} | |||
| \contentsline {subsubsection}{\numberline {2.3.1}Ripped off by temperature sensors}{7} | |||
| \contentsline {section}{\numberline {3}Bom Notes}{8} | |||
| \contentsline {subsection}{\numberline {3.1}SOD323 (diode) is equal to 0805}{9} | |||
| \contentsline {section}{\numberline {4}PCB Build and Test Notes}{9} | |||
| \contentsline {subsection}{\numberline {4.1}Current usage, and Solar Project}{10} | |||
| \contentsline {subsection}{\numberline {4.2}Current Limiting resistor on LT1512}{10} | |||
| \contentsline {subsection}{\numberline {4.3}Separate Grounds 1512}{10} | |||
| \contentsline {subsection}{\numberline {4.4}Switches Max Current}{10} | |||
| \contentsline {subsection}{\numberline {4.5}Usage}{10} | |||
| \contentsline {subsection}{\numberline {4.6}Forgot V Dividers for batteries gt 5v}{11} | |||
| \contentsline {section}{\numberline {5}Rev 2 Build}{11} | |||
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