# Piezo Trigger Switch

#### Joey.Jerry

Joined Jun 8, 2014
53
Hello Everyone,
I'm new to this website and the forum. I've been doing a DIY project in which I need all of your help. I want to make a simple Piezo trigger switch which lights up an LED only when it is been striked. P.S-It should be a simple circuit,the schematics you may provide should be a user-friendly one,i.e,no use of symbols because i cant understand them.So,please use the image of the objects as it is in the schematics(like the image attached).Also,please do not give any suggestion to use an arduino(to make it simpler and cheaper). Also,I've attached an image.Will the image work if its female jack is connected to a male jack connected with a piezo sensor?Please Help me.

Thanks

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#### ericgibbs

Joined Jan 29, 2010
10,509
hi JJ,
You are showing 'blue' leds, these have a typical voltage drop of 3.2V, so 4 in series would require 12.8V to drive them.

But the big problem with your circuit it has no current limiting resistor in series with the leds, they would burn out.

What colour are the LED's.?

E

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#### ScottWang

Joined Aug 23, 2012
6,926
The transistor can be use 2N3904 or other transistor has c >= 100mA.
Assuming that the 12V battery has 13.8V when it is full.
And calculating the current limiting resistor R :
(Bat - Vce(sat) - (3V * 4)) / 16mA
= (13.8V - 0.2V - 12V) / 16mA
= 1.6V / 16mA
= 100Ω
R_Watt = V*I = 1.6V*16mA 0.0256W
So choosing 1/4W is ok.

When the battery drops down to 13V, then the LED current will be as :
I = (13V-12V-Vce(sat))/100Ω = 0.8V//100Ω = 8mA, it is still very bright for a indicator.

You have to measure the Vf of LED to make sure the voltage.

#### Joey.Jerry

Joined Jun 8, 2014
53
hi JJ,
You are showing 'blue' leds, these have a typical voltage drop of 3.2V, so 4 in series would require 12.8V to drive them.

But the big problem with your circuit it has no current limiting resistor in series with the leds, they would burn out.

What colour are the LED's.?

E
Hey,
I was just showing an example with the led. But i'm not going to use any specific ones.Also,never bother about the power,because the image i've attached is not mine.I got it from some website. So,if possible can you instruct me how to convert a piezo into a switch?
Thanks.

#### Joey.Jerry

Joined Jun 8, 2014
53
The transistor can be use 2N3904 or other transistor has c >= 100mA.
Assuming that the 12V battery has 13.8V when it is full.
And calculating the current limiting resistor R :
(Bat - Vce(sat) - (3V * 4)) / 16mA
= (13.8V - 0.2V - 12V) / 16mA
= 1.6V / 16mA
= 100Ω
R_Watt = V*I = 1.6V*16mA 0.0256W
So choosing 1/4W is ok.

When the battery drops down to 13V, then the LED current will be as :
I = (13V-12V-Vce(sat))/100Ω = 0.8V//100Ω = 8mA, it is still very bright for a indicator.

You have to measure the Vf of LED to make sure the voltage.
Hey,
I was just showing an example with the led. But i'm not going to use any specific ones.Also,never bother about the power,because the image i've attached is not mine.I got it from some website. So,if possible can you instruct me how to convert a piezo into a switch?
Thanks.

#### ScottWang

Joined Aug 23, 2012
6,926
Hey,
I was just showing an example with the led. But i'm not going to use any specific ones.Also,never bother about the power,because the image i've attached is not mine.I got it from some website. So,if possible can you instruct me how to convert a piezo into a switch?
Thanks.

#### tracecom

Joined Apr 16, 2010
3,944
Hello Everyone,
I'm new to this website and the forum. I've been doing a DIY project in which I need all of your help. I want to make a simple Piezo trigger switch which lights up an LED only when it is been striked. P.S-It should be a simple circuit,the schematics you may provide should be a user-friendly one,i.e,no use of symbols because i cant understand them.So,please use the image of the objects as it is in the schematics(like the image attached).Also,please do not give any suggestion to use an arduino(to make it simpler and cheaper). Also,I've attached an image.Will the image work if its female jack is connected to a male jack connected with a piezo sensor?Please Help me.

Thanks
I don't have a pictograph, and don't want to spend the time drawing one. My suggestion is that you learn to read schematic drawings if you want to be involved in electronics.

Attached is a schematic drawing of a circuit that uses a piezo element as a trigger. I built it and it works. Maybe someone here will draw a pictograph for you.

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#### Joey.Jerry

Joined Jun 8, 2014
53
I don't have a pictograph, and don't want to spend the time drawing one. My suggestion is that you learn to read schematic drawings if you want to be involved in electronics.

Attached is a schematic drawing of a circuit that uses a piezo element as a trigger. I built it and it works. Maybe someone here will draw a pictograph for you.
Hey,
Thanks for that. I try to study them. Meanwhile if someone draws an east-to-understand schematic,It will be helpful.
Do you have any picture/videos of your trigger switch?
Thank you.

#### Joey.Jerry

Joined Jun 8, 2014
53
Can anyone spare some time for me and draw a pictograph of the schematics attached?

#### ScottWang

Joined Aug 23, 2012
6,926
I was used a piezo buz as your linking page to tried, and it is working fine and the LED lighting up similar as the video you linked.

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#### ScottWang

Joined Aug 23, 2012
6,926
In the beginning that I was used the piezo elements and NE555 to tried, but the logical level needs to adding a inverter(or bjt), so I decided to changed to used the bjt to tried, and it's working fine.

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#### Joey.Jerry

Joined Jun 8, 2014
53
I was used a piezo buz as your linking page to tried, and it is working fine and the LED lighting up similar as the video you linked.

Hey friend Can you draw Pictograph of this schematics because I cant understand them.
Thanks.

#### Joey.Jerry

Joined Jun 8, 2014
53
Hey,
I've just created a schematics(I donno if its correct or not).I've attached it here.
the resistor is 220K
IC is 741 op amps
First Preset is 470E
Second preset 4.7K/5 K
I hope you understood what I've attached.Please tell me if it will work. I would have tried ,but these materials are not available locally. So if you have some time to spare,please try this and tell me the results.Also,if you have any simple circuits,please let me know.
Thanks.

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#### ScottWang

Joined Aug 23, 2012
6,926
Hey friend Can you draw Pictograph of this schematics because I cant understand them.
Thanks.
What you don't understand?

I never draw Pictograph, what's that, is the parts to components?
EE has it's rules, anyone who want to study it then he must be follow the rules.

#### Joey.Jerry

Joined Jun 8, 2014
53

#### ScottWang

Joined Aug 23, 2012
6,926
Where did you get the idea?
What do you respect the op amp to do?
The wired connection didn't like Inverter, or Non Inverter, or voltage follower, what is that?

#### Joey.Jerry

Joined Jun 8, 2014
53
What I actually wanted to make is a Cheap virtual drum kit out of a PC (Qwerty)Keyboard. So,I want to use the piezo to trigger the drum samples from a software called DvDrums.Each piezo will trigger a key on the keyboard.For,example,if I trigger alphabet A on the keyboard with piezo the bass drum sound will be heard. I know it removes velocity sensitivity,But its fine.
I got the idea from an instructable here
http://www.instructables.com/id/WORLDS-CHEAPEST-VIRTUAL-DRUM-at-10-Rs500-us/
Thanks.

#### Doktor Jones

Joined Oct 5, 2011
66
There's a schematic at http://www.electronics.dit.ie/staff/tscarff/Music_technology/8way_drm2/drmpre_ct.gif that looks like it's doing what you want to do. It's from a more complex circuit that actually outputs MIDI signals on a 5-pin DIN and has a microcontroller, but if you used the circuit above wired to the keyboard's controller board that should work.

With a supply current of a couple milliamps, 2x LM324 can easily be driven by the USB power.

DISCLAIMER
I am somewhat of an amateur myself; before following my instructions, I would wait to see if anyone else here has corrections/improvements to make to what I've said

Joey.Jerry:

In that diagram, it shows you a pinout of the LM324; note the pin numbering goes down the left side and back up the right.

The squiggles labeled "R#" are resistors, whose color bands would indicate their resistance -- in this case, R1-R8 are 22K which would be red/red/orange (with a fourth band that is probably gold or silver), and R9-R16 are 1M which would be brown/black/green.

The squiggles with arrows labeled "VR#" are adjustable resistors; these are optional, and used for sensitivity adjustment (probably a good idea to include them).

The triangular sets of lines refer to ground, so all those should be tied together, and should ultimately go to the (-) side of your power supply which, if you're using the USB power, would be the black wire coming from the USB cable. +Vcc should also all be tied together and go to the (+) side of your power supply, which is the red USB wire if you're using that.

The little circles near the "input" and "output" labels are just meant as terminals; in your case you'd wire the inputs to your piezo elements and your outputs to the keyboard controller. Note that one side of each piezo element will go to ground (the terminal circle on the input that goes straight to the ground symbol).

The outputs from the LM324 should drive transistors (such as the ubiquitous and cheap 2N3904) which will shunt a contact from one side of the keyboard controller to a contact on the other side. You will probably have to play around with combinations of contacts to get usable characters (shift, function keys, home, end, etc might not get picked up by the software), and will want to check polarity with a multimeter first so you get the transistor the right way around, but this should do the trick for you.

#### ScottWang

Joined Aug 23, 2012
6,926
I just used LM324 to tried, and it's works, Doktor Jones has a linking page also used LM324, my input resistor is more less as 220Ω, if you want to build it then you have to test one stage first to make sure the piezo elements to match the amplitude of op amp.