CV Tuner
User guideOverview
This is a small firmware that helps you dial in the CV outputs on your Brain module so they're actually accurate. You walk through 0V to 10V in one-volt steps on both channel A and B, nudging each step until the output lands exactly where it should. The values you save get tucked away in the Brain SDK's calibration storage, which means any other Brain SDK firmware you flash later will pick them up automatically.
How to calibrate
What you need
The most reliable way to calibrate is with a multimeter, so that's what this guide assumes. You'll need:
- Your Brain module running this firmware
- A reasonably accurate multimeter (a decent handheld DMM is plenty, and the more precise it is the better the calibration)
- A patch cable from the output to your meter's input
If you'd rather calibrate by ear using a VCO and a tuner, that's covered in Calibrating with a VCO.
Setting up the multimeter
Set your multimeter to DC voltage, on a range that covers 10V (usually the 20V DC range on a manual meter, or just leave it on auto). Connect the black probe to the Brain's ground (any sleeve/ring of an unused jack works), then connect the red probe to the tip of the CV output you're about to calibrate.
That's the whole setup. You're going to step through each voltage and turn the pots until the meter shows the right number.
Calibration process
Controls
The two buttons walk you through the calibration steps and the pots do the actual tuning:
| Function | What it does |
|---|---|
| Button A | Step down 1V (10 -> 0) |
| Button B | Step up 1V (0 -> 10V) |
| Hold Button A for ~1s | Switch output channel |
| Hold Button A + B for ~1s | Save calibration value |
| Pot X | Coarse tuning offset |
| Pot Y | Fine tuning offset |
A couple of things worth knowing. Step 0 is just a reference point at 0V, so the pots don't do anything there, which is expected. Only the channel you're working on actually outputs voltage; the other one is held at 0V so you don't accidentally probe the wrong jack. And after you change steps or switch channels, the pots use pickup behavior, so you might need to turn one a bit before it "catches" and starts moving the offset.
LED feedback
| Feedback | What it means | Details |
|---|---|---|
| LED 1 | Out 1 active | |
| LED 2 | Out 2 active | |
| LED 3 | Unsaved settings (dirty) | |
| LED 4 | Save result | Success: 2 long pulses Failure: 4 short pulses |
| LED 5 | Storage protection | Solid on: protected save allowed Blinking: save blocked |
| LED 6 | Current voltage | Step 1..10: that many short pulses Step 0: one long pulse |
Calibrating, step by step
Start at step 0. Your meter should read very close to 0V, which is just the reference, with nothing to adjust. Press Button B to bump up to step 1, which should output 1V. Watch the meter and turn Pot 1 for coarse changes, then Pot 2 for fine adjustments, until the meter reads exactly 1.000V (or as close as your meter resolves).
Press Button B again to move to step 2 and repeat, adjusting until you see 2.000V. Keep going all the way up to step 10 (10.000V). Each step is independent, so take your time on each one.
Once channel A is done, long-press Button A to switch over to channel B (LED2 lights up). Move your probe over to the channel B output and run through the same 1V → 10V walk.
When both channels feel good, hold Button A and B together for about a second and a half. LED4 will flash two long pulses to confirm the save, and LED3 (the "unsaved changes" indicator) will turn off. That's it, you're calibrated.
Saving and what sticks around
Nothing gets written to flash until you do the deliberate A+B hold, so you can experiment freely without worrying about clobbering anything. Once saved, the calibration survives power cycles and firmware updates, as long as whatever you flash next reserves the Brain SDK storage sectors (most SDK-based firmwares do).
If the save fails for some reason, LED4 will show the failure pattern and LED3 will stay on so you know your changes didn't make it. Flashing a firmware that doesn't respect the SDK storage layout is the main way you'd lose calibration data, so be a little careful with non-SDK firmwares.
Calibrating with a VCO
If you don't have a multimeter handy, you can calibrate by ear-and-eye using a VCO and a chromatic tuner. It's less precise than a meter but works in a pinch.
You'll need a VCO with a 1V/oct pitch input, a tuner (hardware unit or a plugin/app), and a patch cable. Start by disconnecting Brain from the VCO entirely and tuning the VCO to C0 using just the tuner. Once that's set, patch Brain's output A (or B) into the VCO's 1V/oct input and leave the tuner watching the VCO's audio output.
From there the workflow is the same as above. Step up through 1V, 2V, and so on, but instead of watching a meter you're adjusting until the tuner reads C1, C2, etc. Keep in mind that VCO tuning drifts with temperature and the tuner itself has its own accuracy limits, so a meter will generally give you a cleaner result.
Download
Download the latest version from Brain Firmwares.