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1  Topics / Science and Measurement / Re: Problems using the DUE DACs to drive a difference amplifier on: April 12, 2013, 02:12:01 am
I FIXED IT!

I simply powered the board from a LM7805 attached to the same DC power supply the motor controller was attached to. Then I ran the the analog outputs into a quad op amp, which was powred with rail voltages provided by a LM7812 and LM7912. The first two op amps were simply used as buffers, while a third was wired as a summing amplifier with a gain of 3 (so I could use the controller's 10v range).

I guess it's true...enough Op Amps can fix any problem.  smiley-razz
2  Topics / Science and Measurement / Re: Problems using the DUE DACs to drive a difference amplifier on: April 02, 2013, 10:35:13 pm
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?
3  Products / Arduino Due / Re: Arduino Due libraries (official and 3rd party) on: March 31, 2013, 05:04:59 pm
I made a (very basic) library to interface with the FTDI Vdrive2 module. Uses TX1/RX1 for communication with the Vdrive2 and TX0/RX0 to send the responses to the Serial Monitor.

https://github.com/prphntm63/VDRIVE2.git

Improvements welcome smiley-wink
4  Topics / Science and Measurement / Problems using the DUE DACs to drive a difference amplifier on: March 31, 2013, 04:47:29 pm
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.
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