Hackaday Prize Entry: You Can Tune A Guitar, But Can You Reference REO Speedwagon?

Just for a second, let’s perform a little engineering-based thought experiment. Let’s design a guitar tuner. First up, you’ll need a 1/4″ input, and some op-amps to get that signal into a microcontroller. In the microcontroller, you’re going to be doing some FFT. If you’re really fancy, you’ll have some lookup tables and an interface to switch between A440, maybe A430, and if you’re a huge nerd, C256. The interface is simple enough — just use a seven-segment display and a few LEDs to tell the user what note they’re on and how on-pitch they are. All in all, the design isn’t that hard.

Now let’s design a tuner for blind musicians. This makes things a bit more interesting. That LED interface isn’t going to work, and you’ve got to figure out a better way of telling the musician they’re on-pitch. This is the idea of [Pepijn]’s Accessible Guitar Tuner. It’s a finalist in The Hackaday Prize Assistive Technology round, and a really interesting problem to solve.

Most of [Pepijn]’s tuner is what you would expect — microcontrollers and FFT. The microcontroller is an ATMega, which is sufficient enough for a simple guitar tuner. The real trick here is the interface. [Pepijn] modulating the input from the guitar against a reference frequency. The difference between the guitar and this reference frequency is then turned into clicks and played through headphones. Fewer clicks mean the guitar is closer to being in tune.

This is one of those projects that’s a perfect fit for the Hackaday Prize Assistive Technology round. It’s an extremely simple problem to define, somewhat easy to build, and very useful. That doesn’t mean [Pepijn] isn’t having problems — he’s having a lot of trouble with the signal levels from a guitar. He’s looking for some help, so if you have some insights in reading signals that range from tiny piezos to active humbuckers, give him a few words of advice.

20 thoughts on “Hackaday Prize Entry: You Can Tune A Guitar, But Can You Reference REO Speedwagon?

  1. Variable frequency oscillator tuning. Welcome back to 1951. The concept is that when two sins of different speeds peak together, generate click, so if they’re far apart they’re clicking often enough to generate a tone, but it starts clicking at sub-audio frequencies when they get closer to one another.

    Best bet is ditch the FFT, set your vrefs to +/-1v (as guitars like), and when the tone’s wave interval hits zero with a reference interval, click.

    Or you could just analog it. Like it was 1951.

  2. I’ve never met a tone deaf blind musician but assuming there is a need for such a tuner I thing that there needs to be an analogue front-end that the MCU controls. The first thing a user does is pluck the string to establish the envelope for the amplification section, then subsequent plucks can be for frequency detection.

  3. Digital came first not some analog meter showing “0”. Pre or just post war. A strobe tuner is vastly superior to any +0– type of indicator. They are simple to do with an XOR gate, a ref tone and a divide by 2, twice driving a ring of as little as 4 LED’s. That is enough to tell approach and plus or minus. Translate that to tactile points, or use bright LED’s for limited vision. The click in a tactile sense could use two thumpers giving up-down sense.

    However as one else points out, the blind often make good piano tuners.

    1. “If you’re really fancy, you’ll have some lookup tables and an interface to switch between A440, maybe A430, and if you’re a huge nerd, C256.”

      You might have some difficulties doing that with the thing you posted an image of.

  4. Why not use flageolet tones and interference? Tuners are heavily overrated anyway; I’m neither blind nor a music professional but still can tell immediately if a guitar is in tune or not (and adjust it if necessary), not just with an open string but even a chord will do. The only thing I’m using tuners for is for reference…

  5. A real guitar tuner project would replace the tuning pegs with small servos. You’d turn on the tuner, pluck all the strings with a pick, and it would automatically set it to perfect tune.

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