555 Based Piezo Trigger

I’ve always been drawn to drum pads and kits. They are lots of fun and offer a slightly more tactile method of control then rows of pots and switches. So today while I was playing around on my breadboard I was drawn to pull out some piezoelectric disks and start experimenting.  What I’ve come up with is a very simple drum trigger circuit that you can build and experiment with.

This circuit uses a 555 timer set up in monostable mode. A monostable 555 timer will output a square wave pulse whenever it receives a trigger pulse from the piezo disc at pin 2. The pulse output from the 555 can then be adjusted through the 500K ohm pot placed between V+ and pin 7. The output pulse is then sent into the base of a 2N3904 transistor which works as a gate between the audio source and the speaker. This means when the pulse from the 555 is high the audio will pass through the transistor and when the pulse ends and the 555 output goes low the transistor will block the audio from passing.

If you are interested in adjusting the pulse length beyond what is available using the pot this can be achieved by adjusting the electrolytic capacitor between pin 6 and ground. By lowering the value of this cap you can shorten the range of pulse lengths available. Conversely by increasing it you can access a longer range of pulses.

By setting up 4 or 5 of these piezo trigger circuits you could create a fairly versatile set of drum pads. Since the audio source can be switched out or developed further there’s a lot that you can do to expand on the acoustic possibilities of your drum kit. You can try experimenting with different oscillators, Filters, LFOs, White Noise Generators or anything you want.

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555 Oscillators in Series

I’ve been spending a lot of time lately playing around with 555 timer chips and wanted to quickly share my latest creation. This project uses four 555 timers each set up as a standard astable oscillator. I’ve then connected the output from pin 3 of each oscillator to the control voltage at pin 5 of the next subsequent chip. Essentially this means each 555 timer is working as an LFO for the next oscillator to it’s right. I also increased the size of the capacitor between pin 6 and ground of the two left-most oscillators in order to  lower their frequency.

I was quite pleased with the range and depth of sounds it produced however, it should be said that I built this as a proof of concept and it is not fully flushed out. I would be very interested to try a similar setup with a different waveform. I feel like this idea would really come into it’s own if used with a triangle or sine wave oscillator which produced a wider range of tones. I have also been experimenting, with some success, with adding capacitors between the output and control voltage inputs to smooth the square wave slightly and create a saw tooth pattern. Without an oscilloscope on hand however this is proving difficult to optimize.

This is also a circuit which can be easily expanded by adding additional oscillators and admittedly there is a little voice screaming in my head to take it to it’s logical conclusion. I expect in my near future I’ll spend a rainy afternoon stringing together as many 555 circuits as I can fit on my breadboards and see what I end up with. I’ll be sure to share the results.

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