Hello everyone. I have a small 5V relay connected to a PIC via a ULN2803 driver. I have the diode on the 2803 tied to VCC to serve as a flyback diode, and it appears to be working properly. I'm switching 16VAC with the relay's contacts, which are connected to a small motor. The motor pulls about 60mA. The relay's contacts are not tied to the board's VCC or GND in any way - only to the motor and the AC source.
When the relay switches I get a significant amount of noise on VCC and throughout the circuit board. So much noise at times that the PIC actually resets. I'm really at a lost where all the noise is coming from - I would not expect so much induced noise on VCC just by turning a small motor on and off. If I remove the load, the problem goes away.
In the interest of full disclosure, the contact traces on the PCB do not cross VCC in anyway. I do have a ground plane on the bottom side of the board and the trace for the AC source lines is on the back side.
Any suggestions? Do I need a snubber on the relay contacts to kill the noise? If so, any suggestions on R/C values? Any help or constructive suggestions would be greatly appreciated. Thanks.
-Tom
When the relay switches I get a significant amount of noise on VCC and throughout the circuit board. So much noise at times that the PIC actually resets. I'm really at a lost where all the noise is coming from - I would not expect so much induced noise on VCC just by turning a small motor on and off. If I remove the load, the problem goes away.
In the interest of full disclosure, the contact traces on the PCB do not cross VCC in anyway. I do have a ground plane on the bottom side of the board and the trace for the AC source lines is on the back side.
Any suggestions? Do I need a snubber on the relay contacts to kill the noise? If so, any suggestions on R/C values? Any help or constructive suggestions would be greatly appreciated. Thanks.
-Tom