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Zumo - using PWM at 3.3 V


#1

Hi -

I have a National Instruments myRIO. I was trying to use it to control a Zumo - it is a couple of years old so I assume it is using the v1.1 Zumo shield for Arduino.

To perform my test I used jumpers to connect pins 7 and 9 from an Arduino to the corresponding pins on the Zumo and I could control the right motor as expected. When I move the wires from the Arduino to the myRIO and provided the same signal, I got no response from the motor.

The only difference in the signals is that the myRIO provides a 3.3V PWM signal. I looked at the documentation for the DRV8835 motor drive and it would appear that it is expecting a 5V PWM signal becasue it has its VCC (pin 12) connected to 5V.

So two questions… Is my reasoning correct, and is there any simple workaround?

Thanks


#2

Both versions of the Zumo shields do supply a regulated 5V to VCC on the DRV8835. However, the motor driver should work with 3.3V logic signals. According to its datasheet, VIH is 0.5 * VCC, which means that logic signals as low as 2.5V are recognized as logic high. Have you separately verified that the myRIO is generating the right signal (e.g. looking at its waveform with an oscilloscope)? If so, can you confirm that the Zumo Shield and myRIO share a common ground?

By the way, if you have the v1.2 version of the Zumo Shield, it will be indicated on the white silkscreen at the top of the shield, which you can see in this picture.

-Jon


#3

Hi Jon,

Thanks for your reply. I finally got it to work by connecting both the 5V and GND pins on the Zumo shield to the myRIO.