testing calibration

Calibration

• Calibration mode lets you fine-tune the CV inputs and DAC output (channel #4) as well as adjust some basic settings (display offset, encoder direction).

• NB: if you just wish to update the firmware, re-calibration is not required (unless noted otherwise); the calibration values are stored separately from any other settings.

Procedure:

• The calibration menu is entered by keeping the left encoder pushed down during start up / power-on.

• you'll need a multimeter; precision isn't too important, because the DAC output isn't overly high-res/accurate to begin with. (using a good multimeter won't hurt, of course).

• Note that at each step, you click the right encoder to proceed, or click the left encoder to go back one step. Rotating the left encoder clockwise also advances through the calibration steps, and anticlockwise steps back through the calibration steps.

0. setting encoder directions

• Depending on brand of encoder you've used, the encoders might turn in the wrong/reverse direction. If your encoders - left, right, or both encoders - happen to turn in the reverse direction, this can be easily fixed by pressing the lower tact switch once (or twice, or thrice) while in calibration mode. The effect is immediate and will cycle through the following options:

  "normal", "R reversed", "L reversed", "LR reversed"

• Keep pressing the lower button until you find the right setting for your hardware (there are only four possible permutations, as listed above).

• Be sure to store your calibration settings on the last calibration screen (see below) so that the encoder direction setting is persistent - you should never need to set it again unless you revert to the default calibration settings at some stage.

1. use default values?

• The first screen asks whether to use default values or not. If this is the first time you calibrate the module, or if you wish to re-calibrate from scratch, leave the selection at Yes and click (press) the right encoder to proceed. Otherwise, if you just want to adjust or fine-tune your existing calibration settings, twist the right encoder anti-clockwise so that No appears and then click the right encoder.

2. correct display offset?

• The next screen allows you to adjust the display position: some OLED screens are offset by two pixels, some are not (SH1106 vs SSD1306, typically). You should see a complete rectangle around the perimeter of the screen. If not, twist the right encoder until you do, then click the right encoder to proceed.

3. DAC/channel 4

• next up is the DAC, there's five calibration points that have to be adjusted:

  • -4V, -2V, 0V, +2V, +4V
  • connect your multimeter to the channel #4 (D) output (e.g. using alligator clip connectors and a patch cable inserted in the output, or some other equivalent arrangement); and twist the right encoder to adjust the DAC code/output value.
  • the first calibration point is -4V: turn the right encoder until the output is as close as -4V as possible. don't worry if you can't get it exactly right, none of the modes are seriously 'quantizing'. when done, proceed to the next calibration point (-2V), tune it, then go to 0V, and so on.

4. CV inputs:

• the final few step(s) adjust the CV input offsets for each channel.

  • click to proceed to the next page, which will say something to the effect of ADC CV1 / Adjust: with no inputs connected, twist the right encoder so that the value shown is as close to 0 as possible.
  • There may be some jitter and it might jump around between -1 and 0, or between 0 and 1 - that's fine - just get it as close to zero as possible. when done, click to proceed and repeat for the remaining CV inputs.

• Finally, save the results (by clicking the right encoder).

• Power-cycle, and you're set.

testing:

basic functions:

• check the basic functions first: power up the module and patch a clock signal into the main clock input:

  • the display should track the incoming clock and you should see the incoming clock passed on to each of the six clock outputs.
  • the 5 digital outputs should be outputting ~10V pulses, output #4 (= DAC channel) should be outputting ~4.75V pulses. to measure the output level, turn the pulsewidth setting all the way up to 50% (= 50% duty cycle), and set the divider to, say, /32. that should result in a fairly long on-period, which any DMM should be able to register.
  • if you can't see the module responding at all, chances are something is wrong with the clock input. check your soldering around the NPN transistors. if individual outputs fail, check your soldering around the two TL074s.

• if something's not right with your CV inputs, there's a 'debug' menu which can help to diagnose certain issues:

  • long-press the right encoder to go to the 'app' selection menu, then press the left encoder; page 3 of the debug menu (reached by pushing the left encoder twice) will display the raw values returned from the ADC.
  • with no signals patched into the CV inputs, the values displayed should sit somewhere near ~ 2048 (after calibration); they might be a little off before calibration, but not drastically (as in: hundreds of counts).