Feedback mode in jrk21v3

I’m using jrk 21v3 to control a dc motor.
In my project i have a tachometer, and the output of this tachometer is connected to the FB pin of jrk21v3. In Pololu jrk configurity utility i have selected the mode frequency in the feedback mode. I put the engine running at various speeds, but in the graph of the variables the variable feedback is always a straight line at 50%.
What could be happening?


Hello, Carlos.

I’m sorry you are having trouble.

Please try changing the PID period from its default of 10 ms to something longer like 500 ms. This makes the jrk sample the FB line for longer, so the numbers you see for the Feedback variable should vary more. Also, instead of looking at the graph, I recommend looking at the “Scaled Feedback” value which is displayed in the upper left corner because that will allow you to see small changes easily.

You will most likely need to have more than just the FB line connected. For example, everything in your system needs to share a common ground.

Does your tachometer output a square wave? What frequency would you expect it to have? Do you have an oscilloscope so you can look at the signal on the FB pin?