Piezos to control LEDs. Simple, but what components?

[HammerSlammer]

Greetings everyone.
I want to build a reliable converter/controller box. I've been doing this kind of thing, as an electrician for decades, except the devices I used were always for higher voltage. I worked in a high-rise office building, the lighting was controlled with low voltage switches and relays. We used 24volts as the control-voltage for the switches and latching relays, and 277volts to power the lights.

In this project, nothing gets latched. A pulse from a piezo closes the normally-open contacts of a relay. When the contacts close, it completes the circuit that powers a bank of the LEDs. Absence of the triggering voltage causes the relay to open its contacts.

*This is the simple explanation:
In this project, the piezos will be mounted inside my percussion instruments (a set of drums). When a drum is hit with a stick, a voltage is produced by the piezo, triggers a relay, which allows a bank of LEDs to light. The harder the drum is hit, the higher the voltage output of the piezo.

I will probably need an adjustment (a pot?) to reduce false triggering caused by other vibrations. I really don't know if this is going to be an issue, depending on how the rest of the circuit is designed. I DO want the circuit to be designed so that the LEDs light up at lower voltages (lighter taps on the drum), but not so sensitive that a very slight tap, or vibration will trigger the LEDs.

I don't know the voltage output of these piezos (about the size of a quarter), but I'd bet someone in this forum knows. My meter responds to slow to measure the voltage.

Inside the controller box will be 15 separate circuits, one for each trigger input. No, I don't want to get into digital addresses and all that. I need this to be as inexpensive and simple to build as I can get it to be. I don't know enough about electronics, to design this circuit. I don't know what components are out there, or what to ask for when I shop for them.

For the controller box itself, I figure I'll need a decent transformer to convert 120volts AC, to the operating voltage for my LEDs. (I don't know what LEDs I should use). I have a pile of power supplies from old PCs that I would like to use.

For each input circuit, I am guessing that I'll need a transformer to boost the piezo output voltage enough to activate a relay. I'll need a relay for each input, and some sort of a pot to adjust sensitivity. I don't know what kind of pot I need, or where in the circuit the pot should be wired.

If someone can help me out with this, I would be grateful. I am entering a world where I don't speak the language and am a foreigner to electronic components. I think it should be obvious as to what I need help with. Thanks to everyone in advance for your help.

 

[(*steve*)]

First you need to build up one of these on a breadboard, then you can make something larger.

Do you already have any piezo sensors?

Essentially they operate like a microphone, vibration causes a voltage. In the case of piezo sensors, that voltage can be quite high, and is related to the amount of deformation the sensor undergoes.

You are likely to use:

1) some input protection to limit the voltages created and make sure they don't damage anything,
2) followed by some conditioning of the signal (possibly amplification if the signal is as a result of sound, less likely if the sensor is actually being struck)
3) a comparison of the voltage with a reference (possibly adjustable for "sensitivity")
4) some sort of output driver

You'll need

a) a breadboard,
b) assorted components (for these you may not know what you need until you need them -- are you located near a component supplier?),
c) some op-amps (start with a couple of 741's,
d) a power supply (a pair of 9V batteries with clips should suffice),
e) jumper wires (thin wires to poke into the holes in the breadboard to help connect things)

and

f) an understanding of how to construct a working circuit from a circuit diagram.

Do you think that sounds doable?

Depending on your piezo elements, you may also need a soldering iron, solder, etc, to attach wires.

 

[HammerSlammer]

Thank you. This really is the most helpful and friendliest forum I have ever encountered.

I have a bag of piezos. Came with no paperwork. I used these to make drum triggers. Have to solder on my own leads. Have done a lot of soldering.

Not from the planet "electronics" and don't know the language. What I need is specifics:
What do you mean when you say input protection? What do I put in the circuit to get protection? Please don't say "a fuse".

The sensor is not being struck. It will be located below the striking surface. By "amplification", do you mean a transformer to boost the voltage?

I have no idea what you were saying in #3

What do you mean output driver?
What is an Op-Amp?

I want to use the power supply(s) from my old PCs. I have about five or six.

I can read and understand circuit diagrams, as long as everything is labeled. -Thanks

 

[(*steve*)]

Thank you. This really is the most helpful and friendliest forum I have ever encountered.

We try

I have a bag of piezos. Came with no paperwork. I used these to make drum triggers. Have to solder on my own leads. Have done a lot of soldering.

Excellent. Can you explain how they are mounted when used as drum triggers? How will the mouting differ (or will it be similar) for this use?

Not from the planet "electronics" and don't know the language.

No problems, most of us emigrated here at some time and had to learn the language. We do remember.

What I need is specifics:

Yep, I'm just trying to lay down some broad principles first before we jump into specifics.

What do you mean when you say input protection? What do I put in the circuit to get protection? Please don't say "a fuse".

Piezo sensors can generate high voltages (say 90V). This voltage can damage electronics. The input protection is a small circuit that takes any excess voltage and redirects it to where it can't damage anything.

In this case it will be a couple of diodes and a resistor. It may not be strictly necessary, but without knowing the characteristics of the device I don't want to have you destroy the unit in normal use.

The sensor is not being struck. It will be located below the striking surface.

I guess this is also touched on above. As long as it's similar in mounting to the way it is when used as a drim trigger then I guess the signal will be useable.

By "amplification", do you mean a transformer to boost the voltage?

Well, an electronic version of that, but similar, yes.

I have no idea what you were saying in #3

Just a fancy way of saying that you need some electronics to turn on the LED when the sound is loud enough. And you probably want to be able to adjust what "loud enough" means.

What do you mean output driver?

Depending on the LEDs, you need an appropriate means of connecting them to power or their life will be very short. It also alludes to the fact that the circuitry I've discussed up to now is not capable of providing much power. The driver is a special sort of amplifier that is designed to make the LEDs (in this case) perform correctly without damage.

What is an Op-Amp?

It's an electronic device that can do a while host of things, amplifying signals, comparing them, etc. They are a basic building block that is used to replace much more complex circuits.

I want to use the power supply(s) from my old PCs. I have about five or six.

Yep, eventually. But whilst prototyping it's best to start with something that doesn't provide enough power to vaprorise components.

I can read and understand circuit diagrams, as long as everything is labeled.

Great. Are you familiar with the numbering of pins on an IC and how to tell where pin 1 is?

 

[HammerSlammer]

We try



Excellent. Can you explain how they are mounted when used as drum triggers? How will the mouting differ (or will it be similar) for this use?

**The drum triggers are piezos that are hot-glue mounted onto a round piece of 30 guage galvanized sheet metal. The sheet metal is mounted on a piece of 1/4" plywood, cut slightly smaller than the inside of the drum; the sheet metal is cut to about the same size as the plywood. The plywood is mounted inside the drum, about 3/4" below the drum head with L brackets mounted against the inside walls of the drum. The plywood "floats" on a foam rubber bed, located between the L bracket and plywood , icolating it from erroneous vibrations.

No problems, most of us emigrated here at some time and had to learn the language. We do remember.

**Good

Yep, I'm just trying to lay down some broad principles first before we jump into specifics.

**Muchly appreciated

Piezo sensors can generate high voltages (say 90V). This voltage can damage electronics. The input protection is a small circuit that takes any excess voltage and redirects it to where it can't damage anything.

**Going by the other piezos I found by this seller (really cannot be positive) the max output voltage is about 30volts

In this case it will be a couple of diodes and a resistor. It may not be strictly necessary, but without knowing the characteristics of the device I don't want to have you destroy the unit in normal use.

**No problem with this

I guess this is also touched on above. As long as it's similar in mounting to the way it is when used as a drim trigger then I guess the signal will be useable.

** the piezos for this project will be mounted on the same piece of sheet metal, right next to the drum trigger piezo

Well, an electronic version of that, but similar, yes.

Just a fancy way of saying that you need some electronics to turn on the LED when the sound is loud enough. And you probably want to be able to adjust what "loud enough" means.

Depending on the LEDs, you need an appropriate means of connecting them to power or their life will be very short. It also alludes to the fact that the circuitry I've discussed up to now is not capable of providing much power. The driver is a special sort of amplifier that is designed to make the LEDs (in this case) perform correctly without damage.

**You don't really mean "connecting them", as in wire, do you? Also, how do you shorten the life of an LED?

It's an electronic device that can do a while host of things, amplifying signals, comparing them, etc. They are a basic building block that is used to replace much more complex circuits.

** I know what an IC chip looks like in a general sense. I have never messed with one. I think I yanked one out of its socket on a PC motherboard once. Kind of looks like a fat, rectangular centapede, except it has about 10 legs?

Yep, eventually. But whilst prototyping it's best to start with something that doesn't provide enough power to vaprorise components.

Great. Are you familiar with the numbering of pins on an IC and how to tell where pin 1 is?

** Not familiar with ICs. If it's anything like PC components, pin one is marked someway.

 

[(*steve*)]

**The drum triggers are piezos that are hot-glue mounted onto a round piece of 30 guage galvanized sheet metal.

[...]
** the piezos for this project will be mounted on the same piece of sheet metal, right next to the drum trigger piezo

Perfect! This, along with the information you got from the other thread (excellent job digging that up) means the problem is probably easier than I imagined.

**Going by the other piezos I found by this seller (really cannot be positive) the max output voltage is about 30volts

This is easily enough to damage electronics. Fortunately the circuit you found should eliminate that as a problem though.

**You don't really mean "connecting them", as in wire, do you? Also, how do you shorten the life of an LED?

LEDs are quite a bit different to light bulbs. They are easily damaged. See here for lots more information. Read section 0 to start off with.

Kind of looks like a fat, rectangular centapede, except it has about 10 legs?

Yeah, that's them. 8, 14, and 16 legs are pretty common.

** Not familiar with ICs. If it's anything like PC components, pin one is marked someway.

The important thing is that one end will have either a semicircular depression in one end, or a circular depression in one corner.

If the legs are pointing away from you so the orientation mark is visible to you any in the upper (or upper left), then the top left pin is number 1. They then go down the left side 1, 2, 3, 4, and then back up the other so that pin 8 (for a chip with 8 pins) is in the upper right opposite pin 1.