DIY Car Battery monitor

Creating a car battery monitor using Espruino and a few passive components.
Full details and code at www.espruino.com/Battery+Monitor

[@purerizzo]

Fantastic little project, great idea Gordon!

[@jontscott]

Very nice, one little typo on your web site under the section "You'll need" you say "coltage regulator" not voltage... Otherwise very neat. I will try building this for myself as my car battery has also died a few times over the last year due to less use.

[@Espruino]

Thanks! I'll get that changed...

[@StuartDesign]

I'm pretty new to wiring... what do you recommend for making temporary connections with this board (I'm just experimenting not following the project)... breadboard wires seem to jiggle loose even if I bend them... should I just solder? Or am I missing something obvious? Cheers.

[@Espruino]

There are a few interesting suggestions at electronics.stackexchange.com/questions/249140/how-can-i-make-connection-on-pcb-circuit-board-holes-without-solder-for-proto but personally i just poke the wire through the whole, twist it back onto itself and around, If you want to do a lot of prototypes with it I'd consider soldering on pin strip and poking it into a proto-board. However in this case, you're dealing with voltage from a car battery that you *really* don't want to short out or connect to places it shouldn't (if 12v gets on one of the board's GPIO pins it'll kill it instantly) and only 4 connections to the board, so I'd say soldering would be a pretty good idea in this case.

[@AkosLukacs42]

Hey Gordon my first thought is the solar panel can drain the battery. Or do you have a diode? Possibly negligible, but could worth checking. Or dropping in a schottky

[@Espruino]

Yes, I'd been wondering about that, but it turns out my panel has a diode built into it. Either way the nRF52 can actually detect slightly negative voltages so the battery monitor should be able to flag up if something like that is happening. I believe in my case the battery drain is a combination of a ~10 year old battery, alarm that draws a bit too much power, and having had the solar panel in the rear window so it's not getting enough direct sunlight... But now I can see for sure if I've fixed it!

[@AkosLukacs42]

@@Espruino Ten year old battery? You are lucky it starts at all! :)

[@Espruino]

@@AkosLukacs42 I know! Well, I can't see a date code and it's a 10 year old car so I assume the battery hasn't been changed - but I could be wrong. The voltage is fine and car starts great when it's charged though, so I'm blaming the immobiliser for now :)

[@altitude1039]

Interesting idea. What sort of range do you get with Bluetooth? I'll have to see if I can do something similar using Wi-Fi or ESP-Now. My garage is probably too far from my house. Thanks for sharing

[@Espruino]

It's around 20m range - you get more with a good aerial on your BLE dongle or less with walls and stuff in the way. Bluetooth 5 can advertise in a slower long-range mode which can drastically improve that though (I've heard people mention 1km!)

[@altitude1039]

@@Espruino Wow! That's pretty good. Thanks.

[@OlympusHeavyCavalry]

Across the solar panels not the battery? It is supposed to monitor the battery as per the video heading.

[@Espruino]

Yes - the idea is it monitors the car battery but also the charge put into it from the solar panel. Because of the way the voltage drop across the resistor occurs, you need to put Espruino on the solar panel side, since that is supplying power, so will have a higher voltage than the battery. If you power the module from the battery then you'd have to try and measure a negative voltage on the input pin of the microcontroller.