Measuring time elapsed -- guitar tuner response time

Hi. I am a complete Arduino newbie asking for advice on feasibilty and general guidance on this project:

I’m looking to very finely measure the response time of guitar tuner pedals.

Timing would be triggered by the start of an analog audio signal.

End of timing period would end when the tuning pedal responds by lighting the LED display on the tuner, and this light is measured.

I’m guessing that I’ll need:

  • A way to get the guitar signal into the Arduino. Guitar cables use 1/4" mono plugs.

  • A detector that can detect plucking of string (audio signal above a certain threshold?).

  • A detector that can detect when LED is lit (light above a certain threshold?).

  • A way to measure the time elapsed between the two events as finely as possible.

Does such a project sound feasible? If so, I’d appreciate really specific guidance on methods, parts and models.

Thanks,

–John

When you say "as finely as possible" are you talking milliseconds? microseconds? nanoseconds?

What sort of time periods are you talking about? A few seconds? A second? A few milliseconds?

Hi John. Thanks for replying.

Milliseconds would be sufficient.

--John

So you want to trigger when the audio signal passes a threshold and stop the timer when light is detected at the display. I expect you will need amplification on the audio signal to get a high enough signal to trigger n Arduino. I'm not an electronics engineer by training but I would guess that a dual op-amp would be sufficient: one to act as an adjustable gain amplifier feeding a low-pas filter and one acting as a comparator to turn on when the filter output exceeds an adjustable threshold. Then a phototransistor to detect light at the display.

The code would be very simple: Loop until sound is detected. Save the start time. Loop until light is detected. Save the stop time. The difference between stop and start time is the delay. Display on Serial Monitor or LCD or 7-segment display.

Great. Any suggestions for better approaches are appreciated, also.

Do you have specific recommendations regarding particular board and components?

thx

John2338954: Do you have specific recommendations regarding particular board and components?

If it were me I would start with an Arduino UNO clone and a cheap LCD Shield. Mostly because I have both on hand. That takes care of input and output if you don't want to have your Arduino tethered to a PC. For the op-amps I would pick one that runs on a 5V single rail. That would mean doing to DigiKey or Mouser and doing a parametric search. There are plenty of dual op-amp chips in 8-pin DIP packages. If you want an active filter you could get a 14-pin quad op-amp chip. You will need help on the circuits and, as I said, I'm not a trained electronics engineer. Maybe you can find one at a local hackerspace or find one you can hire.

Thanks John. Much appreciated!