Stray inductance?

[zachtheterrible]

I've got two circuits that are exactly the same. They both worked until i put a switch on one of them to turn it off and on. Before i put the switch on it, it worked fine, but now the circuit is malfunctioning.

The switch is panel-mount style, so I had to run some wires from the board to the swtich and then to the PSU. The only thing that I can think of is stray inductance. I tried connecting a 100uf cap across the negative and positive but it doesn't make a shred of difference. I also tried a .22uf cap.

Any other ideas? If needed I'll post a pic of the schematic.

 

[TekNoir]

Contact bounce perhaps?

 

[zachtheterrible]

GOOD GOD IM SUCH AN IDIOT!! thank you so much teknoir!

That has GOT to be it. Any simple way of fixing that? I can't redesign the circuit because the circuit is already on a PCB and mounted in a case. Maybe with a capacitor or something somehow??

 

[audioguru]

Hi Zach,
Contact debounce circuits are common. Post your circuit for us to see what it has to do.

 

[eblc1388]

Contact bounce on a power ON/OFF switch? I'll hold my breathe.

 

[Nigel Goodwin]

Contact bounce on a power ON/OFF switch? I'll hold my breathe.

For a 'hard' switch, that actually switches the power rail, obviously contact bounce shouldn't be any problem. But, if it's a 'soft' switch, feeding into a logic IC that then switches the supply, then obviously contact bounce does apply.

Basically we need to see the circuit!.

 

[stevez]

Here's some thoughts.

It sounds like you were able to demonstrate that the circuit functions ok without a switch - then you added the switch. Take the switch out and see if it still functions. The mechanical process of adding the switch could have done some damage or loosened a connection - or a spike/surge did some damage.

With the switch in place and in the 'on' state you ought to be able to demonstrate that the circuit works just as it did before. If the switch is functioning properly there would be no bounce if left in the 'on' state. Yes, there would be some extremely low ohmic loss in the connections, the switch, the contacts.

If the circuit operates at RF or if timing is an issue then the addition of the switch could change some things. I am not sure if you intended the capacitors to suppress noise/spikes or to cancel inductance. An example: you might have added a switch to the RF section of a small FM transmitter or receiver. At these frequencies the physical addition of the switch would change things significantly.

As others have mentioned - tell us more about the circuit.

 

[zachtheterrible]

Dont have time to post a schematic right now, but the switch is to cut the power to a circuit involving the holtek HT12D decoder.

Sorry for the very small explanation, I'll give more info later :lol: