Piezo Trigger Switch ..#2

Thread Starter

c1pr1ana

Joined Feb 15, 2022
7
If you want to make an independent drum system, it may have too much hardware that you can't do.

The first thing is that you must read some knowledge for the drum, and if you can study the arduino then you can complete your idea for the EE drum with the computer, even developing your own instrument sets using the instrument samples.


My LM324 op amp circuit.


op amp using LM324.


The video of Homemade Electronic Drum Kit : Coltronics Kit-e, 3D to show how the structures of the drum.

The pedal and foot switch.

piezo drum trigger -- images, schematic.

DIY Electric Acoustic Drum Triggers Tutorial for eDrums - The video.

The Drum Kit - Kit lets you turn your Arduino into a drum kit.

Piezo Drum Kit Quickstart Guide.
Good day! What can be added to the circuit so that the pulse duration can be adjusted? Thanks!

Mod: link to old Thread
https://forum.allaboutcircuits.com/threads/piezo-trigger-switch.98418/post-1267617
 

Thread Starter

c1pr1ana

Joined Feb 15, 2022
7
I want to modify a set of electronic drums so that it simulates a keyboard. I made the circuit according to the diagram but the duration of the LED pulse (which will be grouped with an LDR or replaced with an optocoupler) is too short for the keyboard circuit to detect the contact. Can you provide a schematic please? Thanks!
 

MisterBill2

Joined Jan 23, 2018
11,913
I want to modify a set of electronic drums so that it simulates a keyboard. I made the circuit according to the diagram but the duration of the LED pulse (which will be grouped with an LDR or replaced with an optocoupler) is too short for the keyboard circuit to detect the contact. Can you provide a schematic please? Thanks!
If you can show us the circuit that you have, probably a small addition can lengthen the pulse so that it is long enough to trigger the keyboard circuit. That ought to take less effort than creating another circuit.
Also, is it possible that the pulse amplitude is the problem instead of the pulse width? That seems more likely to be the problem, at least that is my guess.
 

MisterBill2

Joined Jan 23, 2018
11,913
I see the circuit, but no hint as to how it is intended to trigger any keyboard function. What is the keyboard iput circuit that you are hoping to trigger?
Certainly this will light an LED, but then what?? If te normal keyboard input is a switch of some sort, then we wil need to know the voltage across the switch contacts when the key is not pressed. And we wil also need to know if one side of the key switch is tied to the keyboard common . The change may be as simple as replacing R1 with a diode and adding a sma capacitance between pin 2 and the common. That wi stretch the pulse a bit.
 

Audioguru again

Joined Oct 21, 2019
4,693
The 220 ohm resistance is WAY TOO LOW for a piezo to drive.
Use a non-inverting opamp circuit (because it will have a high input resistance) and include a clamp zener diode so that a hard hit producing a high voltage does not zap the opamp.
 

MisterBill2

Joined Jan 23, 2018
11,913
The 220 ohm resistance is WAY TOO LOW for a piezo to drive.
Use a non-inverting opamp circuit (because it will have a high input resistance) and include a clamp zener diode so that a hard hit producing a high voltage does not zap the opamp.
the 220 ohms is a SERIES resistor, not a load resistor. It is there to limit the current through the internal protection diodes.
 

Thread Starter

c1pr1ana

Joined Feb 15, 2022
7
Certainly this will light an LED, but then what??
The LED will be grouped with an LDR or replaced with an optocoupler to separate this circuit from the keyboard pcb.
This is the keyboard PCB, the voltage across the switch contacts when the key is not pressed is ~20mV.
keyboard pcb.JPG
I am hoping to trigger a contact between 2 pins to complete the circuit, long enough that the KB pcb to notice the contact, around 0.3-0.5 seconds in my opinion.
For the moment, whit the actual circuit, hitting the piezo is making the LED flash very quick.

I found something else that could work, it's used to light a RGB Led strip at 12V and is adjustable.

FTPE3T8HJAHF15D.pngMy question is: can this be simplified for only one LED and powered from USB from the KB PCB ? I'll need to make like 6 of this for my full drum set.
Thank you again for the interest!
All the best, Ciprian.
 

MisterBill2

Joined Jan 23, 2018
11,913
If only 20 millivolts is across the keyboard switch then it will be a challenge to close that circuit with an isolated device, because the forward drop at low currents is usually more than that. So probably neither side of the keyboard switch is connected to any shared connection, neither positive nor common. To verify that we will need a voltage reading from both sides of a key switch to the keyboard "common", (power supply negative, usually), Scanned (multiplexed) inputs are more complex to work with.
 

Thread Starter

c1pr1ana

Joined Feb 15, 2022
7
I think the contact can be closed with something that act like a relay, i closed the KB circuit with a LDR and a flashlight
 

MisterBill2

Joined Jan 23, 2018
11,913
OK, then it can possibly work with a super-bright LED and the same driver with a diode-capacitor input to deliver longer pulses. I suggest having whatever is used close to the keyboard connections to avoid long leads being added to the keyboard circuit,
 

Audioguru again

Joined Oct 21, 2019
4,693
The negative input of an inverting opamp is called a virtual ground which is zero ohms, because the opamp has negative feedback.
Then your piezo is shorted with the 220 ohms input resistor.

An antique LM324 does not have input protection diodes. Most piezo drum sensors use a transistor and diode with a high value series resistor.
 

Thread Starter

c1pr1ana

Joined Feb 15, 2022
7
Thanks to everyone for the for the suggestions, I have a little request, can you please draw me a schematic (only the area that needs to be modified) so i can understand better what modifications to make. Cheers !
 
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