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Project Notes

#271 cordwood/tuner

Use the Boldport Cuttle & Cordwood as a guitar tuner, with a custom input preamp.

Here’s a quick video showing it in action..



The Cordwood has six LEDs. Six is one of my favourite numbers .. like the number of strings on a standard guitar.

So is it possible to use the Cordwood to detect (even tune) the six strings of a guitar?

I was thinking about doing a complete analogue solution with bandpass filters (probably active filters in order to get very tight passband frequencies). Maybe later, but to start I wanted to try an Arduino-based approach I’d seen in an Instructables article by Nicole Grimwood.

Input Preamp and Filter

I’ve modified the circuit to take an input from an electret so I can use it with acoustic instruments, and adjusted the OpAmp configuration for simple single-supply operation using a basic LM386 audio amp.

The electret microphone is biased with a 10kΩ resistor and coupled to the amplifier with 100nF capacitor.

The LM386 uses a standard 200x gain configuration with a 10µF gain control and 10µF bypass capacitors.

On the output:

  • 22kΩ voltage divider and 220µF capacitor biases the output to VCC/2
  • a low-pass filter at a corner frequency of 723Hz cuts out most of the high frequency harmonics and noise that just confused the tuning algorithms

I mounted this all on a small prototyping board to get a nice clean signal. It is laid out in such a way that it plugs into a breadboard. Here’s the contruction I used:

mic_preamp_front mic_preamp_rear

And a typical output signal (open D string):


Arduino Sketch

The initial code is from the Instructables article by Nicole Grimwood.

I’ve update the sketch quite a bit. It now doesn’t even try to be a tuner, but just a pretty stable and accurate indication of which root note is playing.





Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.