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Original question:

linear analog servo motor drive

LM358: .

Science East
Prodigy 35 points
Part Number: LM358
Other Parts Discussed in Thread: LM393

Hi folks.

I am trying to build a motor speed controller using labview. I got the labview diagram circuit but struggling with the motor circuit. 

 

I am using Arduino uno and DAC (MCP4922). If i connect any component after MCP4922, the voltage drops dramatically.  I want to make the motor operate according to the voltage, but it just working really slow..  I've used different motor to check if it is a motor problem, and i've measured the output voltage using digital multimeter- measuring directly from the DAC, i get the right voltage, but whenever i connect LM358(in above circuit i couldn't find the LM358 so just put it instead) or the diode, only few voltage comes out so the motor is not working according to the voltage we control. I think the problem is that too large current is taking through the motor and can not find the way out. Please tell me how i can make it work. 

  • 0
    Prodigy 35 points

    Part Number: LM358

    Hi folks.

    I am using LM358 to amplify the voltage which comes out from the DAC (MCP4922). I am struggling with the circuit. 

    I am using Arduino and DAC, MCP4922. If i connect any component after MCP4922, the voltage drops dramatically. I want to make the motor operate according to the voltage. but it just working really slow. I've used a different motor to check if it is a motor problem and i've measured the output voltage using digital multimeter-measuring directly from the DAC, i get the right voltage, but whenever i connect LM358 (In above circuit i couldn't find LM358 so just put it instead.)  or diode, only few voltage comes out . So the motor is not working according to the voltage i control. I think the problem is that too large current is taking through the motor and can not find the way out. Please tell me how i can make it work.

  • 0
    TI__Guru*** 149556 points

    SE,

    Please provide measured voltage values and note which node(s) was measured.
    The most striking error is that motor and M1 is powered by 0V. The motor positive and FET source are both grounded.
    I have not checked MCP4922 data sheet, but I expect shorting VOUTA to ground is not correct usage.

  • 0 in reply to Ron Michallick
    TI__Guru*** 149556 points

    South East,

    U3A is labeled at LM393, LM358 would be better.

    This circuit will make motor current control more controllable. It is a voltage to current converter.

    Add a resistor 5M resistor from 5V to pin 2 if you need a true zero current point.

  • 0 in reply to Ron Michallick
    Prodigy 35 points
    We've solve the problem! Thank you so much for your help. We've added FET to amplify the current and the motor starts to run according to the input voltage.