Using a single momentary C/O switch - diyAudio
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Old 21st December 2011, 04:59 PM   #1
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Default Using a single momentary C/O switch

I know this is going to sound a bit backwards, but if you can bear with me you will see the logic in my question.

As its Xmas I'm not going to be able to order many bits so I am stuck with what is in my parts bin.

I have available a rather attractive toggle switch that would look rather nice on my pre-amp front panel. the problem is that its a centre biassed single pole changeover switch.

As my design intends to use relay switched inputs.

Has anyone got any clever ideas as to how to the switch ?

My best estimate would be to debounce the outputs and use the outputs to trigger a decimal UP/DOWN counter. Then to use the outputs of the counter to drive the relays.

I've yet to find a decimal UP/DOWN counter that I can limit to a count of 2 possibly 3.
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Old 21st December 2011, 05:36 PM   #2
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Unfortunately we don't know what's in your parts bin.

Typically counters can be limited in their count by detecting a particular number (with a fallthrough AND/OR array) and generating a signal to drive the (master) reset, this could be as simple as connecting bit2 to the reset giving a count of 0, 1, 2, 3, 0, 1,... but you need to AND bits 0 & 1 to give a single output at a count of 3 plus you need to discriminate between a count of 2 and a count of 3 (1 AND (NOT 0)). Consequently most people have a few NAND or NOR gates which are versatile.

The easiest thing is if you have a PIC programmer (everybody should) and an 8-pin PIC (12F508). I use PICs all over the place to do simple logic functions such as the one you describe.

Sorry about the edits, I had some of the bit numbering wrong...

Last edited by counter culture; 21st December 2011 at 05:41 PM.
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Old 21st December 2011, 05:37 PM   #3
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I am not sure what your switch does: Is it (on)-off-(on) or on-off-on, (on) is momentary or a spring return function.
A Boolean truth table would be helpfull. E
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Old 21st December 2011, 05:47 PM   #4
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Normally the Common Centre Pin is NOT CONNECTED to either OUT 1 or OUT 2.

You can depress the switch in either direction making contact with OUT 1 in one direction or OUT 2 in the other.

It always returns to the centre position when the Common Centre Pin is NOT CONNECTED to either OUT 1 or OUT 2.
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Old 21st December 2011, 05:50 PM   #5
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It doesn't really matter, NO or NC if you're connecting it to a clock input...
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Old 21st December 2011, 05:55 PM   #6
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I'm looking for a simple design that can simply CLOCK up or down through three options reliably.
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Old 21st December 2011, 05:59 PM   #7
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I've got to go out, but I'll draw you something if nobody else has before I get back...
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Old 22nd December 2011, 02:53 PM   #8
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I thought a simple S-D Debounce circuit with two NAND gates might work but it doesn't ?

What I need is a Bi-Stable with debounced clock input.
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