Big Easy Driver: it is possible to regulate the output current by using Arduino?

Robotics
1

Hi again,

by going deep into my project, I realized that the required torque to keep the load static is quite lower than the torque required to move it.

So, immediately, an idea had came to my mind “what if I could reduce the current when no movement is requested?”. Doing so I could also reduce the temperature of the stepper itself. That would undoubtedly benefit in hot environments.

I’m using a small but “torquy” NEMA11 stepper: 19Ncm of holding torque, 1.3 A per winding, 3.3V (nominal).

As I understand, after manually setting the potentiometer of the BED to get the required output current, that output cannot be changed by using my Arduino.

I also noticed the TP1 pin just aside of the potentiometer that can be used to measure the output voltage.

My question: what would happens if I attach that pin to a digital output of Arduino by using a resistor? Will I observe a reduced current by setting the pin to low?

By looking at the schematics, the added resistor (R_ref = 40K? 50K?) should go in parallel with the resistance of the potentiometer. So the total resistance should be less than before, and the output voltage should decrease.

Maybe I missed something? There is any elephant in the room? :?

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As you can imagine, I would like to allow the program to reduce the current (for example) of 20-30% in value when it is not necessary (i.e. the stepper shaft is static). On the other, by setting the pin to HIGH, I could have the full torque available.](Vref-mod hosted at ImgBB — ImgBB)

2

That should work; I have done something similar with a DAC to make a fixed voltage regulator into an adjustable one by creating a summing junction at the feedback node.

/mike

3

So, seems that the overall idea could work!

I will take a try in the next days. My main conceirn is about using the pin of Arduino as a sink. I’ve read somewhere that Arduino can “absorb” max 20 mA of current when used as a sink (or it was 40 mA?). I hope this will be enough.

I will have to find the right value for the resistor “R_ref” by trial and error approach, since my potentiometer is not fully turned clockwise when I’m driving the stepper with full torque. So I presume I have around 8K-9k Ohm of resistance in parallel with R_Ref.

4

Hi Gimpo, were you able to control the coil current on the fly with the arduino?

5

I still have to test it. No free time until now because of the pressure from my job. It’s an hard period for me

I’m curious too to see if it works. It should.