Interference in the circuit - Electronic Circuits Projects Diagrams Free

raitl · 21st December 2008, 06:51 PM

I am making a new bot and using two geared DC motors. In my last bot I used steppers so I did not run into this kind of problems. But now my circuit is flooded with interference when the motors turn on. I actually killed a PIC mecause of that. So now I bought an oscilloscope just to sort this out. As I have never used an oscilloscope before, the instrument is still new to me.

Ok, so I have two ceramic capacitors, 100nF each, connected between each motors supply pins. And connecting the oscilloscope probe to the positive of the circuit, and the probe ground to the circuits ground, oscilloscope voltage range set to 20mV and Time/DIV to 1ms. The image I am seeing is this:

Now I have tried 220nF and 1uF capacitors across the leads, but the results are about the same. So how do I get rid of that motor noise in my circuit?

be80be · 21st December 2008, 07:17 PM

Do you have blocking diodes on your motors

raitl · 21st December 2008, 08:06 PM

Yes I do. This is my motor control board circuit:
There is an error on this schematic which I have corrected. I am now using pull-downs on all I/O lines.

be80be · 21st December 2008, 08:28 PM

Take a look at this site Reduce Motor Noise

raitl · 22nd December 2008, 01:13 PM

Thanks a lot! I managed to get the interference down to 40mv now. Going to solder a new PIC into the circuit tonight and see how it will behave.

be80be · 22nd December 2008, 02:17 PM

Put you socket in for your pic

raitl · 22nd December 2008, 02:31 PM

The socket rises the PIC too high. Even though I have a low profile socket. It is a tight fit as it is

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21st December 2008, 06:51 PM	#1
raitl	Interference in the circuit I am making a new bot and using two geared DC motors. In my last bot I used steppers so I did not run into this kind of problems. But now my circuit is flooded with interference when the motors turn on. I actually killed a PIC mecause of that. So now I bought an oscilloscope just to sort this out. As I have never used an oscilloscope before, the instrument is still new to me. Ok, so I have two ceramic capacitors, 100nF each, connected between each motors supply pins. And connecting the oscilloscope probe to the positive of the circuit, and the probe ground to the circuits ground, oscilloscope voltage range set to 20mV and Time/DIV to 1ms. The image I am seeing is this: Now I have tried 220nF and 1uF capacitors across the leads, but the results are about the same. So how do I get rid of that motor noise in my circuit? __________________ Here...let me improve it for you! Puff of smoke ....oops...

21st December 2008, 07:17 PM	#2
be80be	Do you have blocking diodes on your motors

21st December 2008, 08:06 PM	#3
raitl	Yes I do. This is my motor control board circuit: There is an error on this schematic which I have corrected. I am now using pull-downs on all I/O lines. __________________ Here...let me improve it for you! Puff of smoke ....oops... Last edited by raitl; 21st December 2008 at 08:07 PM.

21st December 2008, 08:28 PM	#4
be80be	Take a look at this site Reduce Motor Noise

22nd December 2008, 01:13 PM	#5
raitl	Thanks a lot! I managed to get the interference down to 40mv now. Going to solder a new PIC into the circuit tonight and see how it will behave. __________________ Here...let me improve it for you! Puff of smoke ....oops...

22nd December 2008, 02:17 PM	#6
be80be	Put you socket in for your pic

22nd December 2008, 02:31 PM	#7
raitl	The socket rises the PIC too high. Even though I have a low profile socket. It is a tight fit as it is __________________ Here...let me improve it for you! Puff of smoke ....oops...