Pulse Generator - (does not do what it says on the tin)

I'm planning on building a bass drum module, and I will need a pulse generator to test it, so I knocked up a circuit based on a 555 timer in ASTABLE mode and put it in an Altoids™ tin.

You can easily find a circuit for this just googling around. I drew one up in Kicad like this.

As I wanted this to be a pulse generator for triggering a drum circuit, I wanted the frequency range to fall within a range that would be useful for music, which is calculated by a combination of R1, P1 and C1 in the circuit diagram above. There are plenty of on-line calculators that will help here. I used this one http://www.ohmslawcalculator.com/555-astable-calculator (P1=R2 in the calculation). I found that a combination of R1=3K3, P2=1M and C1 as 2µ2 gave the best range for my purposes (approximately 0.327Hz to 198.761Hz).

I had a small piece of perfboard offcut that I tried to squeeze it onto, and here is the layout.

For the output jack, I used a 3.5mm jack I salvaged from an old PC sound card and epoxied it in place. The location for the output jack was chosen to help prevent the battery sliding from around too much. Here are shots of the internals and the externals.

The adjustment is quite sensitive for the most useful range of pulses, so it might work better with a log tapered pot, but I only had linear available.

Oh, and one more thing. It didn't work with the first battery I tried which was pretty depleted at about 5.5V, so a fresh 9V battery is preferred.

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