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The latest version uses a push button on port B0 of the PIC to trigger an IRQ to cycle between different fade rates. The MOSFETs generate a lot of switching noise, enough to trigger the push button input, and to wipe out HF radio reception.
I've added a 0.1u capacitor and 100R resistor in series between each transistor's drain and source, which has had little effect. I also have 0.1u and 10u across the PIC's power/ground pins, and 0.1u, 10u and 4700u across the 12V DC supply. One transformer winding drives the 5V and 12V DC, the other 3 windings each drive one lamp.
Question is, how else to reduce radiated noise? A screened enclosure and a mains filter will reduce noise outside the device, but will have no effect on noise affecting the microcontroller.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
This is where an oscilloscope would be very helpful. Depending on how it is connected up it could be ground bounce where currents in your ground wires will cause a voltage differential between different ground points that is affecting the microcontroller.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Is there some reason you cant run the lamp from DC? It would need 4 diodes and a cap, but would get rid of one of those MOSFETs and would be a cleaner solution in my opinion. Right now you have significant inductance in the 24V coil that you are switching on and off, which is likely the cause for all the noise. Switching a resistive lamp should really be very easy provided its a DC source powering it.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I agree with that. Also if it is still wired like this: then you have the making of a radio transmitter/receiver that is quite likely to make problems.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hey DM,
You probably need to slow your MOSFETs down! Use bigger and bigger resistors in series with the gates to slug the switching speed, until the level of RFI is acceptable, or the switching losses are unacceptable, whichever happens first
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Suppressing Dichrioc Lamp/Mosfet Switching Noise
