The Digital Harp…

This little project has been in the making for a couple of weeks now and finally it is completed, so here it is and I hope someone out there can find this information helpful atleast.

So what is the digital harp? Well the idea evolved from a thought train of creating a dynamic and complex music instrument that could be controlled by the fingers yet while not touching a single string/key/button/pie and produce a vibrant and beautiful sound. So after a bit more thinking I came up with a compromise to my ambitious thoughts and
managed to bang together a digital harp consisting of four “digital” strings, a ukulele and a very very simple synthesizer.

So very simple.

Using four LDRs and a voltage divider circuit which a transistor sensing the increase in voltage drove a solid state relay I was able to create a very small and easy control circuit for when a hand moved in front of the LDR and blocked its light source from the laser.

I created the oscillator using a 7414 chip which is a Hex Inverter with Schmitt trigger inputs and put a resistor in between the input and output legs and a capacitor. This oscillator provides a square wave output, unfortunately square waves don’t produce the best quality sounds but for this project it worked okay, though if you have the time and the parts I would recommend building a sinusoidal wave oscillator as they sound a lot better.

I setup four of these oscillators for each of the digital strings and then their outputs into the one amplifier.

This is the square wave oscillator setup:

Then its just fitting everything together onto the ukulele which was basically done using a hot glue gun. I removed the nylon strings and tuning pegs, put a on/off switch on the side with a LED… its not a real project if there are no LEDs, and fixed a 6.5mm audio socket to it as well so I could plug it into my guitar amplifier.

I haven’t drawn up an official schematic yet but I do plan to in the near future… if anyone is interested in it let me know, it might just help with motivation.

There are a few little problems with it at this stage but it is practically working as expected and is a great little tool to annoy friends.

Until next time!