Hi All,
As you can probably see I am new here and have been an enthusiastic electronic hobbyist for many years. Recently I decided to get a Rigol 1054z and now I am looking at different circuits to see whats going on visually, its all quite exciting and reminds me of my old college days using Picoscope.
I built a simple motor driver circuit using a PIC 12f1840, it takes an ADC input from a potentiometer and copies this across to the duty cycle of a 15khz PWM output, steered to RA5 for convenience. I am using a cheap motor shield i bought on Amazon for a few quid, an IBT-2, a cheap Chinese H-Bridge and buffer circuit.
Here is my circuit minus programmer lines:
And this is a schematic I found on the web for the IBT-2 board:
The IBT-2 board is connected to a 6V supply, separate to my PIC power supply, and the motor is a cheap 6v hobby motor so nothing high spec with a 0.22uf cap soldered across its pins to help reduce noise (was used on an old project).
I attached my scope probe to the PWM out of the PIC to see the duty cycle.
Turning my POT to around 30% the scope starts to show some noise:
Would you agree that this is what motor noise looks like?Why is it faded compared to the rest of the trace?If we crank the POT to around 60% duty cycle something interesting happens, the motor starts to WAH clearly struggling to keep to a steady output speed and the scope shows this:
My interpretation is that this is more severe noise, can someone confirm that this is correct because it is interested it has also dropped to 0V line as well now? My hypothesis is that the noise is now causing the PIC to reset hence the drop down on the scope and the WAH of the motor.
Interestingly, if you change the timebase of the stopped trace the the noise disappears, this is the same shot as above with the timebase changed once on hold:
Can anyone give me a reason why the Scope suddenly removes this from the plot, even if you change the timebase back the noise is now permanently gone?Another questions is that if the motors and H-bridges have a seperate power supply, why is there any noise present in the circuit, I assumed that would isolate them, can the H-bridges 'leak'?Sorry for so many questions but I do find this all very interesting and would like to know whether my beliefs are correct or maybe I am completely wrong!
Thanks.