My Arduino car gadget uses the OBD-II UART board (1st link below). I’ve seen the docs for the STN1110 chip on that board (it interprets ELM327 commands) (2nd link below). On page 3, the docs say the chip offers “UART interface (baud rates from 38 bps to 10 Mbps”. The ELM327 command to set the UART baud rate is STBR (e.g. STBR 115200). I can set the baud rate, but my gadget shuts off all power when the engine is off, so as to not drain the car’s battery. So it seems to me, the STN1110 would NOT remember the last-used UART baud rate? The default is 9600. So if I want to use higher baud rates, after a power up, I need to open serial comm at 9600 baud and then issue STBR 115200. Is this correct? I mean the UART serial comm baud rate, not the OBD protocol baud rate, which works fine.
That sounds correct - the easiest way around this is to leave the device constantly on (cigarette wiring, etc)…car batteries are huge; it should be able to standby on only a few mA (car batteries have ~80k mAh…should be able to run for 2 months or so?)
I had my Arduino car gadget plugged into the car’s OBD which delivers 12V even with the engine off. But the Arduino drew ~130mA (yes) which, if I didn’t drive the car much, drained the battery in ~2 weeks. I rewired the gadget: now it’s 100% off when the engine is off. The OBD board is in the gadget’s enclosure (for easier handling), so its power is the same as Arduino’s: off if the engine is off. I could split the power, so that the OBD board is always on via OBD (low power if the engine is off). This would keep the settings on the OBD board when the engine’s off, while the Arduino would still be 100% off. But I think I’ll leave it as is, for simplicity.