Freematics Forum

I purchased an OBD-A back in September and just now got to using it. I developed my particular project initially without the OBD as there was a lot to do beyond just getting the speed and in the end, that should have only been a few lines of code. But once I tried, it just hung up on obd.init().

To weed out variables, I go a fresh Arduino UNO and loaded it with obd_uart_test.ino from OBD2UART (commit 243b5fa4ddd06b845a68abccb0a109584cf0fa38).

I have the green wire connected to D0 (RX) and white connected to D1 (TX)... though I also tried those swapped. Then I connected ground to Uno ground and powered the Uno itself off USB. I then used an FTDI serial to USB adapter connected to A2 and A3 so I could get the serial debug output.

Unfortunately, all I get is the following (I enabled DEBUG as well):


Sending ATZ

Timeout
Sending ATL1

Timeout
Sending ATH0

Timeout
Sending ATRV

Timeout
Sending 0100

Timeout
Sending 010C

Timeout
Sending 0902

Timeout

Init...
[127724]ATZ
Init...
[142726]ATZ
Init...
[157729]ATZ
Init...
[172732]ATZ
Init...
[187735]ATZ
Init...
[202738]ATZ
Init...
[217741]ATZ
Init...
[232744]ATZ


One thing to note, (see https://goo.gl/photos/ZxkvDJ3GaUwXyTpLA). Just in case this matters, the V1 adapter I got looks more like the V2, minus the microUSB port and the label on it and has green and white UART wires instead of yellow and white like the docs say. Just mentioning in case I am mistaken about which version of the device I have.

Also, I started probing around to make sure everything was connected correctly and found that the white and green RX/TX wires coming from the OBD have continuity with about 40 ohms impedance between them. Without seeing the circuit schematic I have no idea if this is correct, but in my experience I've never seen that between RX and TX on a UART... so I'm wondering if there is something faulty with the device.

Happy to provide any other details you may need if the would prove useful.

Thanks so much for making this! Looking forward to getting my project working

Did you connect GND together?

Yes, as I stated above: "Then I connected ground to Uno ground "... and I also connected the ground of my FTDI adapter to the ground on the Uno.I verified continuity between the grounds with my multimeter.
Also, the only light on the adapter that comes on is the red LED and it does blink once every time an AT commend is sent from the obd_uart_test.ino

Can you comment as to whether there should be such low impedance continuity between RX and TX on the OBD adapter? If that is expected, then great, but I have never seen that so it concerns me here.

Because every character is echoed unless ATE0 is sent, you receive what your send to the adapter.