I am wiring this up, and I would like to limit the current being drawn from 18v DC/DC converter.
What would be the simplest way of doing this?
this post was submitted on 04 Sep 2025
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The L298 has two sense pins. Connect a current shunt between each sense pin and ground and you can measure the motor current. Use an op amp to amplify it and measure it with the ADC in the microcontroller. The microcontroller can stop the motor if the current gets too high.
That sounds very cool - and way beyond my own understanding :-)
Is this something you could actually help with sketching out for me?
I found the datasheet for the L298 and I can see that for my use (I am using just out 1 and out 2) it should be pin 1 (Sense A) that should be relevant, right?
This looks like it is connected to gnd on the driver board (I can easily cut this connection).
Unfortunately I don't understand what a current shunt is? :-)
It has me slightly worried that it says that pin 1 can go to -1v which I think would break the ADC input?
As far as I can tell the ADC input on the PICO accepts from 0 - 3.3v right?
Thanks a bunch for looking at this!
A current shunt is a resistor that can handle the full current of the motor. You would probably want a 0.1Ω resistor rated for at least 1 watt.
You measure the voltage drop across it to determine the current. The voltage will be quite low. With a 0.1Ω resistor and a 2A load, it will be 0.2V. You want to amplify that up closer to the full scale input of the ADC to get a decent resolution. An op amp with a gain of 10 would work well for that. Use a rail to rail op amp that can run from the 3.3V power supply.
Here is a schematic:
R4, D1 & D2 protect the op amp input from any spikes the motor produces.
Sorry I forgot to ask: I should cut the SENSE-A connection to ground right?