Newby questions - power from OBD II?

For my first project, I wrote an app to get the battery voltage and push it out to the particle console via “publish()”. I ended up with 2 questions that have me scratching my head:

  1. Should my carloop be getting power from the OBD II port? I would have though it would, but I had to plug a USB cord into my cigarette lighter/power port to gain power. Without this, there was no time (car on/off/acc) where the LEDs on the Photon lit. This seems like a significant drawback? For reference, the car is a Nissan Leaf, and the bluetooth reader I plug into it works great (ie, gets power from the port).

  2. Is there something that needs to be done to convert the value from the “battery()” call? The value I’m getting back is 4.xx, which is obviously not correct.


  1. carloop does take its power from the OBDII port on pin 16. It also is ground connected to both signal ground on pin 5 and chassis ground on pin 4. It probably should NOT be connected to chassis ground…

Getting deeper into the power issue, there are some protection diodes, capacitors and a voltage regulator to 5V in the power circuitry. The Photon/Electron/RedbearDuo is powered from the 5V and then outputs 3.3V. The CAN transceiver chip uses both 5V and 3.3V.

It looks like you need to do some troubleshooting. Can you try it on another vehicle and see if it works there? It should work when the vehicle is turned on to supply 12V to the OBDII port. If it still does not work, then you need to check the 5V and 3.3V on the carloop board. If it does work on another vehicle, then you need to check the connector on your car.

  1. I am confused with how you are getting any value back with issue #1. Sorry, I missed the part about the USB cord. In that case, any value you get back is meaningless until the carloop is fully powered. I assume this will work correctly once you get issue #1 solved.

Thanks for your reply cyclin_al1. The confirmation that it should be powered by the OBDII port is good to hear. I’ll investigate further this weekend. Hopefully I don’t have a defective carloop adapter.