# Piezo Power!

Discussion in 'The Projects Forum' started by Impathy, Jan 25, 2008.

1. ### Impathy Thread Starter New Member

Jan 25, 2008
3
0
Hey everyone!

I'm revisiting an old project that I abandoned due to lack of time and knowledge. I've looked everywhere but I assume what I'm trying to do is too advanced for a starter like me. So here's my problem: I have a piezo transducer. When deformed, it generates a small voltage. Roughly around 3v. That's the simple part. I've also got a powerful light on its own separate circuit. This light requires 125v to be fully powered. My question is this, how do I make the voltage of the light depend on the input voltage of a piezo. For example, the piezo is idle, no deformation is being applied. Therefore it outputs 0v. The light should have an input of 0v. Now say the piezo is being fully deformed and is putting out 3-5v. The light should now be at a full 125v input.

Is this possible? And if so, should I try and tackle this as a novice? I've been trying to teach myself electronics over a long time and must be missing something because I can't understand all of the technical jargon when attempting this project.

I understand that I cannot use a transformer in this situation because the amperage would be very low and unusable. Is there a way to solve this?

2. ### nomurphy AAC Fanatic!

Aug 8, 2005
567
13
Off-hand, I doubt that you can do it safely without additional circuitry such as a sensing circuit that drives a relay. A triac could work, but you need to interface the crystal to the triac gate without lending the operator to shocking possibilities -- or making your piezo sing -- some type of isolation is needed.

Try looking up IC's on capacitive touch switches for lamp control.

3. ### SgtWookie Expert

Jul 17, 2007
22,201
1,807
I discourage novices from working on circuits that are above around 50V, as the power levels involved can be quite lethal.

I suggest that instead, you experiment with lower voltage circuits, such as using LEDs or 12V lamps and PWM circuitry.

4. ### Impathy Thread Starter New Member

Jan 25, 2008
3
0
Thanks for the help. I had a feeling that I shouldn't be meddling with 120v lights I've made a circuit that works with a 12v LED light just by adding a transistor to the circuit. That was wonderful, it just didn't put out the brightness I need for this project. So from what y'all are saying, it doesn't sound like there's a safe and easy way to achieve this with my limited skill set?

5. ### SgtWookie Expert

Jul 17, 2007
22,201
1,807
It is better for a young Jedi to experiment at low V levels, because otherwise The EMForce will surely smite thee.

I think you'll be surprised at how much voltage you can get out of a piezo device. Try building a rectifier bridge for it, and use a small cap with a high voltage rating to accumulate a charge. Whack your piezo a few times, and check the voltage you've accumulated with a DVM.

If you connect the piezo up to an audio transformer (the speaker side) you can generate quite a spark (high voltage) at the other end. It's very low current though, so it's relatively harmless (except for CMOS/JFET/MOSFET devices; it'll kill those.)

6. ### Impathy Thread Starter New Member

Jan 25, 2008
3
0
So I have a long way to go before I finish this one. I'll stop where I am and start learning more about electronics and then pick this back up. However, if I were to do more research, what components should I look in to so that I may some day build this? I'm very unfamiliar with triacs, but would that be the answer? Any help is appreciated! Thanks.

7. ### SgtWookie Expert

Jul 17, 2007
22,201
1,807
Triacs, SCRs, power MOSFETS, IBGTs, there are many devices that one could use for such a thing. There are a number of unsafe designs floating around on the web for things like color organs, which are similar to what you intend to do - but as I said, many designs are unsafe. One big clue is whether or not they have a transformer incorporated into the design; if not, it is unsafe.

Some designs rely on capacitors to limit line current. If the cap should happen to fail as shorted, the rest of the circuit becomes connected to line current.

It is a fact of life that all electromechanical devices will eventually fail. It's not a matter of "if it fails", only "when it fails"... so do your best to design your projects with that in mind, as sooner or later some parts will break on you.