M3H256 on Rspberry PI 5 bookworm i2c issue


I wanted to get the Motoron M3H256 to work on a Raspberry PI 5 (OS bookworm). I seem to have some issues with the I2C connection that I don’t seem to get around and can’t find a solution for in the Raspberry 5 documentation..

I have the Motoron board powered with 6V and the raspberry pi is powered seperately. So I managed to get to step Pololu - 3.3. Enabling I²C on the Raspberry Pi.

ls /dev/i2c* gives /dev/i2c-1 /dev/i2c-11 /dev/i2c-12

But when I do i2cdetect -y 1 I see

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

So it seems that the raspberry pi didn’t detect the i2c on the right address. I’ve checked group permissions and that includes i2c, but the raspberry pi 5

The raspberry pi 5 have changed quite a bit to their gpio port handling (configuring serial on gpio 14/15 was an real pain), so I’m sure there is something in the configuration that we are missing. I also have a raspberry pi to my disposal in case all fails. But I just want to put it out there since the documentation doesn’¨t mention that it excludes any raspberry pi type.


Have you been able to use your Motoron with any other boards yet? Could you post some pictures of your board that show all of the soldered connections and let us know what the LEDs on the Motoron do when you try to use it?

- Patrick


No I haven’t used it on any other raspberry pi yet other than the RP5 I have now. But if necessary I’ll be able to easily acquire a RP4 to try the motoron on as well. Just let me know if you’d like me to try that, I’ll just need to flash a new sdcard for it though.

Here above is a picture of my setup. I have an 6V power-source on the VIN and Gnd (tested that with a multimeter) and some simple brushed motors attached to M1 and M2. Yellow LED is blinking and red LED is solid (those that light up on the picture), but interestingly no response on any of the LEDS near the the green connectors.

We tested the M3H256 with a Raspberry Pi 5 here, so we know it should work, but we do not see any obvious issues with your setup so far. It might seem silly, but please make sure that your Motoron is plugged in correctly to your Raspberry Pi GPIO header (the Motoron’s header should cover the 20 pins on the left side of the header, and leave the 20 on the right side exposed) since is hard to check that in your picture.

Can you try out your Motoron with another Raspberry Pi, or could you try out another I2C device with the same Raspberry Pi? Do you have an oscilloscope you can use to check for activity on the I2C pins?

- Patrick

Yes they are covering all of the 20 pins on the left (right now on this picture).

I can try the Motoron on the RP4 I have available, but currently I don’t have an other I2C to my disposal. I have an oscilloscope available at our office so I’ll be able to test the current test setup as well. I hope to get on that this Friday, or else it will be the week after if that is okay.

But thanks for letting me know that you have succeeded to get it to work on a RP5, at least that in particular is not the issue here.

I didn’t had a ossciloscope to my disposal, but I did have an logical anyliser. Perhaps a bit too much but at least I’m able to analyze te signals.

Upon startup both SDA and SCL were pulled high on idle. So the I2C-SDA (GPIO2 on RP5) does respond if I use ‘i2cdetect -y 1’, but the SCL does not do anything. I’m not an embedded electronic engineer myself, but some of my colleagues are and explained to me that at least the SCL should start responding after this request? Or do I need to try out a different function call.

Haven’t tried on a different RP yet.

For I2C, the SCL signal should only ever be generated by the master device. If you are not seeing any activity on SCL, that might suggest something is wrong with the Raspberry Pi’s SCL pin, so I think the next logical step is for you to test your Motoron with a different RPi.

You might also consider looking at the I2C signals with the Motoron disconnected. I think it is unlikely, but if you start seeing SCL activity in that test, then that might indicate an issue with your connections or the Motoron somehow preventing your RPi from driving SCL low.

- Patrick


I’ve tested the Motoron with a RP4 and now I see the right address for the i2c device. Also it responds to the python scripts with LEDS but no respons with the motors yet, but that might be due to another issue (bad connection, not enough voltage to Vin)

But I guess that concludes at least this support as I can now take the next steps to get the motors running and it’s no longer related to I2C. Thanks @PatrickM for your help so far!