Simple Tuner is a hand-held device to help when you’re calibrating a VCO volts per octave trimmer.
Still a prototype, I have a functional device on stripboard and a PCB on order.
Usual procedure for calibrating a volts per octave oscillator is to input some voltage, note the frequency, add a volt exactly, note the new frequency, and hope it comes to an exact doubling. Then you adjust the trimmer and keep trying until it reads a doubled frequency with 1 volt added. That’s V/O tracking.
I find setting up to be able to add exactly one volt, then repeatedly noting frequency changes to be a hassle, so this is a device made to output exactly 1 and 2 volts, and do all the frequency counting and calculation for us. Five LEDs light up to say if the tuning is a little sharp or a little flat and it flip-flops every half second while you focus on the calibration trimpot.
The VCOTuner from TheSlowGrowth is also really good at this, if you have an audio interface to a computer handy, and a midi to CV output so it can drive the VCO around. Standalone without a workstation PC nearby though I’m going to need a hand-held arduino device instead.
Somewhat inspired by the LMNC VCO with a built in tuner, that LED readout is very convenient to show high vs low without asking the user to math.