Piezo to transistor switch to relay switch

[conleycd]

I'm trying to figure out the best way to do this project.

I am wanting to make a piezo to transistor switch circuit - preferably capable of switching a relay.  In a similar manner a circuit capable of producing a momentary switching action (normally open to closed and then open again) would be nice too.

This is my purpose in all of this:

I want to make a box that would allow a drummer to plug in a piezo pad to hit, which would switch a relay (shorting + and - DI output of an audio click) to shut off a click (running through in-ear monitors).

Our band (and I'm sure some other bands as well running in ear monitors) need to play to click (either for backing tracks), to allow the drummer to not have to keep time on a hit hat or ride during quiet moments, or for better editing ability in the context of live recording.  However, if the band (or the drummer gets away from the click) there needs to be an easy way of shutting it off (and potentially turning it back on).

If I could create a momentary switching action I could also hook up a switch in parallel to the click device's (i.e. Korg Beatlab or Tama's - which seems to always break) tap tempo button.  This would allow a drummer to hit a piezo pad to "tap in" timing --- without fiddling around too much with start/stop buttons.

So... I found this http://www.discovercircuits.com/PDF-FILES/PIEZOSWITCH2.pdf

Seems reasonable but I'm unclear if this produces a momentary pulse or latches.

P.S. I know to connect a diode oppose the terminals of the relay to protect the transistor.

Any thoughts?

CC

 

[PRR]

> pulse or latches.

Latching needs two transistors.

You need a toggle flip-flop after this.

The 0.1uFd and 5Meg give a fairly long pulse related to hit-energy, maybe over a second, too long for tap-tempo input.

 

[conleycd]

So the circuit produces a pulse switch about 1 second in duration.  Does the transistor stay in this high state?  Is this why a flip-flop is needed?

If I reduce the resistor value doe I obtain a shorter duration?  I could probably experiment with a base resistance and a potentiometer to get the timing right.

I was thinking potentially of a relay that latches with a momentary switch but typically to do the opposite action it requires an opposite switch on the other contacts.

I'm also thinking I need a piezo that is not too susceptible to false positives (trigger happy).

I guess a simple but expensive way to do this is to use a trigger to midi brain and then use a midi to relay circuit.  A lot more guts for a rather simple task.

CC

 

[sahib]

Pulse producing circuit/transistor does not have to stay in high state. All you need is a pulse long enough to trigger the flip-flop. The link you gave offers two options, positive and negative going pulse. Looking at it in another way, it pulls up or pulls down the output momentarily.

As PRR said you need a flip-flop with a steering (toggle) mechanism. Flipflop has two outputs. When one is high, the other one is low. You use only one output to turn the relay on/off.

Check out below link. Replace the floor switch with the second circuit which pulls down.  Replace the LED with the relay.  

http://www.freeinfosociety.com/media.php?id=1936

 

[Gus]

You might want to look at the circuit in the kid sneakers that light up leds with foot steps.

 

[conleycd]

I'm reviewing potential options.  My hope is that I can use CMOS or TTL logic IC even if I have to then drive a transistor.  The transistor based flip flops just look like a lot of stuff for a relatively simple function.

CC