Leds and buttons working, no sound, no midi, no screen [SOLVED]


I got a weird behavior with my latest Shruthi build, this time I decided to try a newhaven OLED display (the ones from mouser usually advertised here), and flash the ATMega myself.

The filter board is an old dual SVF, which is probably still working and calibrated properly (used to be with my old Shruthi control board).

I flashed firmware 1.02 using the following commands:

  1. set the fuses
    avrdude -P /dev/tty.usbmodemfd1211 -c avrisp -p m644p -e -b 19200 U efuse:w:0xFD:m U hfuse:w:0xD6:m -U lfuse:w:0xFF:m

2) burn the bootloader and firmware
avrdude -P /dev/tty.usbmodemfd1211 -c avrisp -p m644p -e -b 19200 -U flash:w:shruthi1_1.02.hex:i -U flash:w:muboot.hex:i -U lock:w:0x2f:m

So here’s what I get: when I switch on the Shruthi, it takes some time before leds 3 and 7 light up, OLED screen remains fully black.
The buttons seem to react properly, although I find them a bit slow (like I need to hold them a very short while before it changes the led-page, but maybe its me, I used to have firmware 0.97 before). If I go to the mod matrix page, L6 blinks properly, turning pot 1 changes the blink pattern.
From that, I’m deducing that my ATMega was properly flashed, and is working.

OLED remained black, I removed the OLED, and behavior remained strictly identical.

There is no sound to be heard on the output, midi is apparently dead, and I have a feeling the encoder is not working either, hard to tell though without screen but jam mode did not seem to launch after a long press.

I checked all solder joints on the control board, seems fine, all ICs are properly inserted (double checked).

Any leads?


Could be that the fuses are not correctly set and that the MCU is working from the internal RC oscillator rather than the quartz.

Thanks for the hint! I will try to brush up on avrdude to check what fuses are actually set on the chip and report back.

All good now Thank you Olivier!

Note about my command lines above: slight mistake when setting the fuses was an unwanted space between - and U :wink: