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piezo trigger switch circuit

Piezo Trigger Switch Circuit

Piezo Trigger Switch circuit described here is a microcontroller-compatible shock/impact sensor switch module works on 5VDC supply. The whole circuit can be assembled on a 5×7 cm common circuit board. The piezo-ceramic element (PZ1) can also be mounted on the PCB without any difficulty. The module gives a “Logic-High” (H) output when the sensor (PZ1) detects a valid shock/impact. By default, this high signal is available for a period of near 1 second. However you can change this by modifying the value of the RC time constant components in the CMOS monostable circuit built around M7555CN (U1).

One 5mm LED (LED1) is added for effective visual indication of the output status. Imagine the fun you could have building a drum kit and then rocking the house.This circuit lets you turn your Arduino into a drum kit. Discotheque lights, winkling in tune with the bass drum bang is another application example!

Related Products: Electromechanical Switches | Switch Other Switch Piezo

Schematic of the Shock/Impact Sensor Switch Circuit

piezo trigger switch circuit

Proposed circuit board wiring layout is shown here. First of all apply a thin amount of glue to the marked area on the PCB and press a plastic washer (of suitable diameter) into the glue, put aside until the glue is hard. Next, apply little glue on the top of the washer,place the piezo (with presoldered wires) and solder the wires to the circuit board. Decide how you would like to route your wires before you complete this step. It will be harder to move the wires thereafter. Now you can finish the construction by soldering remaining components as indicated in the circuit diagram. After construction, gently hit or knock the piezo sensor with your fingertipor a small hammer to test the circuit. Every time the piezo element receives a hit, the red LED lights up for near one second. Note that the piezo element can easily get damaged, so hit it mildly.

Parts List

  • IC1: M7555CN (from NXP)
  • D1: 1N4148
  • LED1: 5mm/3mm Red
  • PZ1: 27mm Piezo-Ceramic Element (Piezo-Disc)
  • R1: 4.7M ¼ w
  • R2: 100K ¼ w
  • R3: 100K ¼ w
  • R4: 1.5K ¼ w
  • C1: 1KpF (102) Ceramic
  • C2: 10uF/16V Tantalum
  • (Plastic Washer for the Piezo: 25mm outer diameter x 20 mm inner diameter x 2mm thickness)

Notes

  • Detection sensitiviy of this circuit is intentionally reduced to a large extent. Ambient vibrations will not trigger the circuit
  • M7555CN is the CMOS version of IC555. Decoupling capacitorat pin 5 of the IC is not very necessary for this version
  • If you are a skilled hobbyist, try to build the circuit using SMD components. This will reduce the module size and increase the circuit stability. Part Number of U1 in SO-8 package is M7555CD (prototype tested with both packages)
  • Since piezo transducers can output high voltage signal, it is a good practice to include zener diode protection at the input of the circuit
  • Practically don’t expect precise results from this circuit. If your application requires simple sensing this might be a great choice and money saver!

7 Comments

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  • Leslie

    Hi thanks again for your comments.
    Read all the tutorials you suggested and more. Read four different 555 timer-LED circuits and three 2Transistor Monostable Multivibrator ( MMV ) circuits and none of them say that the LED will light when battery is connected. Still couldn’t see why the Led lit after battery is connected and before piezo is activatedin your circuit and the 2Transistor circuits. Doesn’t happen with a simple switch MMV, circuit. Thought that possibly the battery pinged the piezo to ring and the negative portion of the waveform triggered the 555. But built a two transistor MMV circuit without a piezo, http://www.electronics-tutorials.ws/waveforms/monostable.html and the LED lights when battery is first connected too, suggesting it’s not the piezo!
    Would like to really understand why the LED lights in these two circuits but not the simple switch 555 MMV.

    thanks again
    Les

  • Leslie

    thank you for the quick response and thanks for trying to teach me how to fish! nice explanation in http://www.learningaboutelectronics.com/Articles/555-timer-delay-before-turn-on-circuit.php
    I built a similar 555 with a switch, no piezo , http://www.instructables.com/id/555-Timer/step3/555-Monostable-Mode-circuit/
    The LED did not come on with initial power but only after switch was pressed in contrast to yours. I was asking why in the “switch circuit” no initial light but in “piezo circuit” it lit first then went off as per the RC and would light after piezo was hit. I would like to incorporate this nice feature in the “switch circuit” and also to understand why it happens. Reading the above tutorial was very informative but didn’t see how to do it, was that the “tweaking” you mentioned?

  • leslie-saintlouisradnet-com

    Thanks for the response, after the initial lit LED goes off, impulse to the piezo works fine! My question is why does the LED initially light before the piezo is activated? This in my case is good, says circuit is on/working. Is it because #4 is connected to Vcc?

    Thanks again,

    lasl

  • leslie-saintlouisradnet-com

    Hi built the circuit, checked all the parts and connections, when I apply power the LED first lights for about 1-2sec then goes off. the piezo does nothing! Even if the piezo is bad the LED should not light. Using a 9V battery (same thing happens with 6V btw), there is 2.4V across the LED and 7.4V at #3 pin.What did I do wrong? Please advise

    • T.K.Hareendran

      As the LED first lights for about 1-2sec then goes off, we can assume it’s working! What next is just hit the piezo, and observe the response of the circuit (please go through the article again). The circuit should give a “Logic-High” (H) output when the sensor (PZ1) detects a valid shock/impact. Incase of an error, try to replace/rewire the piezo circuitry.

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