Main on/off switch for amp using a piezo switch

I'm stuck with a quite annoying problem.

I've tried to use Schurter PSE M24 piezo switches for use as a main on/off switch.

Link to switch PSE M24


When I first saw these Schurter piezo switches with their ring LED illumination I couldn't resist. The first problem -->price!
The price I paid for two of these babys, someone else is already doing a complete project for. I payed about $200 for one pair. If it were just the price it would have been my smallest problem but........ getting these switches to do what they are planned for is another thing.

I wanted to use them as main switches for on/off. So my idea was to use a simple JK-FlipFlop (Logic IC 7473), connect the output to a transistor and switch a relais. I've done this already a few times with normal mechanical switches and always no trouble at all. It's just a few minutes work to adjust the two resistors (see picture below) to their optimum value and that's it. But this time ......no! These piezo switches output a variable pulse between 20 to 1000ms depending on how hard you press them. I've spent days to look for the optimum values for the two resistors to find a compromise which works with all impulse lengths but ....nope....no chance!

I'm already loosing my will to carry on so any help on this subject is appreciated.

Thanx
using_e
 

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I didn't think up to now to put J, K and CLR on high. Is this really required? Currently they are just not connected. Could this be the cause??? What could happen if they are just floating?

The original layout where I have this idea from also didn't make any reference on putting these contacts on high. I also used this layout already two times with mechanical switches and no problem at all.

The switch has a resistance of <20 Ohm during ON position.
The switch has no bounce and noise should also not bee the cause. I'm currently feeding this test setup from a good lab supply on 24V and a 7805 for the IC.

I will try to put the mentioned contact on high and report back afterwards but unfortunately I will have no time for this before the weekend so I will report back on Saturday.

Thanx
using_e
 
Ok, shame on me, I know I should have thought first before posting my last statement.

It's just that I took this circuit from a homepage a few years ago and it has already worked for me this way two times without any problems (using a mechanical switch). Please don't ask me now how this is possible with J, K and CLR floating I don't know for myself. It just worked until now with this new piezo switch.

Next time it would maybe be better not only to copy the circuit from someones hompeage but also to have a look at the function table of the data sheet of that IC. :headbash:
Now it seems obvious but I didn't think of looking into the data sheet cause it worked before.

I will put J,K and CLR on high and report back on Saturday.

Thanx alot
using_e
 
Ok here are the results:

I put J, K and CLR on high and ........no change....sorry.

I seems that if you don't connect J,K and CLR and leave them floating that they go internally on high somehow. Otherwise it would not function without connecting them.

There is not the slightest change to before.
I will try to experiment a little bit further and also have a look at the mentioned circuit for the soft switch 2. Maybe this can help me to improve my version.

Any further suggestions are welcome.
 
Ok it's done. I've exchanged the JK FlipFlop in my layout with a D type FlipFlop like Maxhawk uses in his design. Now the switch works like he should. Just don't ask me why.
The only real difference is that the JK is negative edge triggered and the D type is a positive one.

Thanx
using_e
 
Piezo Switch Issues

Hi,
We manufacture a ring illuminated Piezo switch with a steady 125mS. The only issue I would see is that you may want to debounce the circuit for anything less. We can also spec a longer pulse if needed. We sell these switches in the states for about $40 USD depending on shape and color... maybe a slight bit more.

We also hold the patent on most of this technology making the other solder their connections to the discs which causes failures down the road.

Hope this helps!

Ted