Add support for bm5v2

[Murphy-Cameron]

Add support for BM5 v2.0 12V Battery Monitor

[zuckschwerdt]

This looks really good, thanks! Some minor style changes, then good to merge.

• First line of the doc-comment is a heading. The next sentence (Sold as…) should have a blank line before it.
• if blocks should always be in braces {…}
• Line 66 ){ should have a space: ) {
• Float ops need to be float, prefer multiplication if possible, e.g. * 0.000625f; // divide by 1600
• Model needs to be in alphanum-dash-alphanum format, e.g. BM5-v2
• keys should be somewhat descriptive (longer) and have a unit symbol as suffix, e.g. "health_pct", "charge_pct", "battery_V", "starting_V"
• parts of the name/description that are generic or a class should be lower case, e.g. "BM5 v2.0 12V battery monitor"

[Murphy-Cameron]

Thanks for the feedback. I've made the requested changes.

[zuckschwerdt]

Perfect. Line 84 needs to be inside the braces :)
And "device_id", "Device_ID", should be "id", "Device ID",, that's it.

[zuckschwerdt]

Oh and the two voltages likely should have a format of "%.2f V",, right?

[zuckschwerdt]

Sorry, havn't noticed this before:

• Shifts need parens for clear operator precedence , e.g. int volt1 = (b[7] << 8) | b[6]; // Current voltage
• If you really have signed char for temperature you need int temp = (int8_t)b[5]; // Temperature in C, signed char in byte 6

[Murphy-Cameron]

Thanks for catching that. My C skills are pretty rusty :-)

[Murphy-Cameron]

Your comment about the signed temperature value prodded me test my assumptions. (We haven't had any temperatures quite below zero C yet). So, I pulled the sensor out, and put it in the freezer. Turns out the temperature is stored as sign-magnitude in byte 6 of the data packet.

I fixed the temperature handling, and added one more sample signal to the tests repository covering the sensor at -1_C, with a cranking error triggered. (pulled the EFI fuse to simulate a failed start attempt).