How to use a one-shot pulse to close SPST momentarily?

[composition4]

Hi,

I am designing a circuit (with the help of http://www.geofex.com/Article_Folders/pffootsw.pdf).

So far I have got enough to up with short pulse of +5v coming from a CD40106. I want this pulse to close a SPST amp footswitch contacts momentarily (and re-open the contacts once the pulse falls again).  I know I can do this easily with a momentary relay, but would prefer to do it with solid state. I was thinking a transistor (but only know how to switch a voltage, not two contacts) or CD4016/CD4066 (but don't know how to make it close the two contacts only momentarily).

So, long story short, how do I use a CD40106 pulse to close a SPST switch momentarily?

Thanks in advance, any help is much appreciated.
Jonathan

[composition4]

Hmm, just looking around

Would an optoisolator be good for this?  One end of the control LED tied to ground, the 5v pulse goes to the other end of the LED.  The phototransistor would have its emitter and collector connected to the two contacts of the footswitch.  I guess I could leave the base not connected to anything?

When no pulse, LED is not lit and the phototransistor is off - hence the footswitch contacts are not connected.
When the pulse is sent, the LED flashes and turns the phototransistor on momentarily - the emitter and collector allow flow hence the two footswitch contacts are connected.

Will this work or do I have a gross misunderstanding of how optocouplers work?

Thanks
Jonathan

[gez]

What does the footswitch do/how is it set up?  Schematic? (segment will do) Without knowing the detail, it's difficult to advise.

[composition4]

Sorry, I didn't think to explain that. And now I don't know why I said footswitch..

basically I'm making an effects looper and it will also change my amp's channel.  The amp uses a momentary tip to sleeve connection to swap back and forward between channels.

For reasons I won't bother explaining, I need to close the tip-sleeve connection using a one-shot momentary pulse from a CD40106.

Now that I think about it, can I just send the pulse to the base of a normal BJT transistor, and connect the collector and emitter to tip and sleeve? And emitter to ground I guess so that the pulse flows current from base to emitter to turn on the transistor?

Thanks for the reply
Jonathan

[gez]

Now that I think about it, can I just send the pulse to the base of a normal BJT transistor, and connect the collector and emitter to tip and sleeve? And emitter to ground I guess so that the pulse flows current from base to emitter to turn on the transistor?

Yes, so long as there's no significant voltage across the jack.  Also, you need a resistor from the pulse output to the base of the tranny and possibly a cap from base to ground to ramp the switching if there's any switching noise.  I tend to use MOSFETs for these things.

[composition4]

Yep cool, thanks muchly for that. Probably the simplest solution for me.

Any particular reason why a MOSFET would be better than BJT?

Jonathan

[Cliff Schecht]

Yep cool, thanks muchly for that. Probably the simplest solution for me.

Any particular reason why a MOSFET would be better than BJT?

Jonathan

MOSFET's make the best switches, hands down. In terms of switching speed, efficiency, really low on resistance and really really high off resistance you can't beat a MOSFET.