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philgda
Joined: 01 Mar 2007
Posts: 2
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 01 Mar 2007 19:51 PWM motor controller |
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Hey,
I'm looking for a little bit of help here...any input is greatly appreciated.
I'm attempting to build programmable PWM motor controller using a pic16f690 and an LMD18200. I've programmed a set of instructions I'd like the motor to follow in the pic and the LMD18200 drives the motor. I have a momentary switch connected to an input pin on the pic. The program is set to loop infinitely and blink an LED until the switch is pressed. Then the program runs (it moves the motor back and forth a few times and then returns to the blinking "wait" mode)
I built the circuit shown in the link below (without the switch shown). Everything works fine with a small case fan connected to the circuit and the voltages behave as expected with no load however when I connect a motor that draws a significant amount of current (1A) the circuit stops working ( I believe I am well within the specs of the motor driver and power supply).
When there is a larger motor attached, the circuit just resets. ie the motor moves slightly and then the program goes back to the blinking LED without completing the preprogrammed tasks.
I thought adding a cap across the pic power pins would help but still the same problem (3300 microfarad).
Hope that is enough info to get some ideas. If not feel free to ask questions about missing details.
Thanks in advance
Replace the ** in the link with tt
http://picasaweb.google.com/philgenereux/Mc/photo#5037008466074414082
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saeed_pk
Joined: 20 May 2006
Posts: 121
Helped: 2
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| 01 Mar 2007 20:08 Re: PWM motor controller |
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Hi
I seen the picture i m not very much familiar this H-bridge but does this stop Back EMF when motor is stopped or commanded to change direction
if it happens when motor is intended to change direction then it is Back EMF you must have a Diode Compensation that would stop the reverse direction current or one more thing that you isolate the Power supply of motor with that of controller
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philgda
Joined: 01 Mar 2007
Posts: 2
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| 01 Mar 2007 22:11 Re: PWM motor controller |
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Thanks for the reply...I forgot to mention that the circuit works as intended when separate power supplies are used. ie one power supply for the motor driver and one for the logic circuit.
I don't want to have two power supplies...any suggestions as to how I would isolate the motor driver from the pic controller?
Added after 1 hours 49 minutes:
Hey all,
I fixed the problem. I just added another capacitor (3300 microfarad) across the output of the power supply. Apparently the current draw of the motor at startup was enough to bring the supply voltage low enough to reset the microcontroller.
Just thought I'd close out the post so it isn't left open ended.
-Phil
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