This build uses an Arduino Pro mini microcontroller, (all code is provided).
This project was undertaken for the charity Remap, which provides custom-made equipment for people with disabilities.
Begin with an LED electronic guitar tuner. I used a Cherub Guitar Mate (WST-550), which cost about £10 from eBay. It was a good choice for this project as it worked well and, as it uses through-hole LEDs, it was quite easy to solder to.
Use a microcontroller (Arduino) to read the LED's then output the information as a series of tones through a headphone.
Using the tuner
When it is turned on, the tuner will play a scale to let you know it’s on.
If the tuner is set to semitone tuning mode it will play 4 low-frequency flat tones.
When a guitar string is sounded, the tuner will play the note it believes the string is playing before either playing three sharp or three flat tones, depending on whether the string is sharp or flat.
The duration of these three tones will depend on how sharp or flat the string is (long tones if the sounded string is very out of tune, short tones if it is nearly correct).If the string is in tune, the tone associated with the string will be repeated.
A specific string can be selected by pressing the button on the back of the tuner, the tuner will cycle through the strings to be tuned. It will then only give feedback tones (as in default mode, above) once the correct string is played.