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Topic: Problems using the DUE DACs to drive a difference amplifier (Read 3 times) previous topic - next topic

prphntm63

Hello

I am using an Arduino Due to temporarily control a tensile testing frame. The motor is driven by an Advanced Motion Controls 20a14 Analog Servo Drive (http://www.a-m-c.com/download/datasheet/20a14.pdf). From what I gather from the datasheet, the +REF and -REF voltage input with respect to REF ground proportionally controls the current going to the motor. So I wrote some code to use a joystick to control the DACs on the due, buffered them through an op amp, then connected the first DAC to the +REF and the second DAC to the -REF and the REF ground to the Arduino ground.

When nothing is connected, an oscilloscope shows that the voltage reading from +REF to -REF coming out of the op amp ranges from +3.3v to -3.3v, depending on the position of the joystick. However when I connect the buffer to the Servo Drive, the motors randomly speed up and slow down with little regard to my input with the joystick. An oscilloscope reading from +REF to -REF shows the voltage is randomly fluctuating.

Any ideas on how I can rectify this? I can provide code and/or circuit diagrams (if needed) once I get back to my apartment after the holiday weekend.

VT

This might be your opamp picking up the noise from the driver and going crazy because of that. Test what's coming from the DAC. Try out the servo drive alone. Try getting rid of your opamp and connect it to arduino simply through a resistor.

prphntm63

See, that was actually the first thing I tried, and it did the same thing except worse.

Do you think adding decoupling capacitors on the Op Amp supply lines would help any?

VT

interesting...
The caps across opamp supply are always a good idea. Connect them.
You may also try bypassing diver's inputs with RC low-pass filter (be sure to place the C very close to the driver).

Please share the schematic and the photo of your actual system.

arduinoadrian

Quote
"I can provide code and/or circuit diagrams (if needed) once I get back to my apartment after the holiday weekend."


Did you return already?
Posting the schematic will help.
Perseverance is 90% of the solution. The remaining 10% is more perseverance.

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