Re: Switch de-bounce circuit questions.

From: Rubicon (no email)
Date: 11/08/04 

Date: Mon, 08 Nov 2004 06:52:20 GMT

On 6 Nov 2004 22:01:45 -0800, wrongaddress@att.net (Bill Bowden)
wrote:

>(Rubicon) wrote in message news:<418dc8b9.720652@news.netaccess.co.nz>...
>> Hello,
>>
>> I have put together a switch circuit using two tactile switches with
>> 555 de-bouncers to a positive edge triggered flip-flop controling
>> transistors/mosfets.
>>
>> The on-board tactile switches work fine but I have also added pins for
>> off-board switches.
>>
>> With off-board switches what do I need to do in addition to using
>> shielded wires to prevent false triggering? Twisted wires caused the
>> switch circuit to flip-flop when a fluorescent light was turned on.
>>
>
>Did you use a termination resistor at the flip-flop input?
>If the trigger signal is from a 555 timer, you can use a fairly
>low value resistor at the flip-flop input, maybe 1K will help.
>The resistor will short out the noise on the long wires.
>
No Bill I did not. 1K approx to V- at F/F input.

>> In addition I have LEDs indicating the flip-flops output ON state but
>> how do I indicate the OFF state with LEDs? Formerly I used a double
>> pole switch.
>>
>
>If you have access to both sides of the flip-flop, you can use the
>other side to indicate the off condition.
>

Unfortunately the other side if the F/F has an identical 555 trigger
circuit.

I can't help but think that it's a waste of a 555 timer here - perhaps
I should have gone for a transistor/resistor/capacitor circuit
instead?

Cheers,

Andrew.

>-Bill

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