I2C not connected on header

We were attempting to connect an i2c sensor via the 40 pin header (p702) but noticed that sda and scl were not giving any output. To confirm this I checked continuity of those pins to the pi and had none. I did note the i2c oled did have continuity. This prompted me to removed the motor control board, I noted that R16 and R17 are missing (0 ohm jump resistors to enable i2c on the 40 pin header). We have motor control board rev 5.2 and after checking 2 other robots we have I have noted the same R16 and R17 connections to be missing. I have seen no documentation on this and was wondering if it is expected to need to solder jump these pads?

Those 2 jumpers isolate the I2C bus from the much larger 50 pin connector, P702 that leads to our expansion connector normally only used for our ‘Sonar Board’.

I put those there to limit the length of the I2C bus since we had no usage of the bus on our Sonar board.

You can either use 0 ohm 0603 resistors or even thin wire to put in R16 and R17. I have not evaluated the I2C for that usage but if you do that please note that it is wise to keep the I2C bus as short as it needs to be. As an example it would be not a good idea to run that bus for longer than lets say 20 or so cm from the connector if at all possible.

Now let me state that we have a few different little boards that have been developed with only one of them as a ‘product’ at this time. These boards sit under the OLED display and offer expansion ability. Can you share with me the sort of thing you are trying to put on the I2C bus and it may be the case we already have a solution depending on what you require.

The most flexible of the boards which I have a couple of and is as of yet ‘unreleased officially’ offers digital IO expansion including relay drivers for up to 12V relays, a few on-board LEDs, a couple tiny switches and JST style jacks for your own wiring including I2C jack on that board. It also has 4 channel ADC and 2 channels of DAC (ADC and DAC both 3.3V). The released board has a few digital lines to jacks, 3 leds viewable from the front and a BNO055 IMU. It has an unloaded pads for a different IMU.

If it sounds like this sort of IO is all you need, send an email to support@ubiquityrobotics.com and I can offer more details and pictures and so on. In the subject of that email please put Request details on I2C Expander boards

Thanks, Mark

IMPORTANT: The 50 pin connector has live battery voltage on it even with the switchboard power off! When you are doing any wiring on the 50 pin P702 have your red lead from the battery disconnected from the battery.

When you take out the motor controller board it clearly state you must remove red lead from battery for this reason as well.

We have a document to discuss MCB board removal here Board Replacement | Learn Ubiquity Robots and ROS