Random values

I’ve finished building my shruti and it sounds great. Only problem I have is that the values of the parameters switch. For example, when I’m in the filterpage the menu cycles trough the the available options without touching the pots. Could it be that I damaged the IC’s and if so wich IC is most likely to be damaged? The leds and push buttons are working correctly.

One question that might help me diagnose the problem: when you set all pots to the minimum or maximum value, does it stop flickering?

Likely candidates:

  • Bad connections on the connector, on the <SEL and <ANL lines.
  • Bad connection or soldering point on the ADC input of the ATMega328p (especially if you still get random values with all pots set to 0).
  • One of IC3/IC5 damaged. If the push buttons are working correctly, IC3 is probably fine.

I would check for the connection, though…

Thanks for the info. I did some further testing, the problem starts to occur when I put a midi signal on it(play notes). When the knobs are turned to zero, the problem disappears. And when I’m in the load save menu I can switch to load, but not to save.

And the orange led blinks irregular when I’m playing the midinotes. The blinking seems to have something to do with the changing of the screen.

You mean it doesn’t appear to blink at 120BPM (or whatever is the tempo set to)?

I’ve tracked the problem a bit further. It has something to do with midiclock. If I put the bpm on external and don’t send a midiclock to it, the problem disappears. If I put the clock to internal and play midinotes from an external keyboard the screen freaks out on every first tick.If I send a midiclock from my sequencer (protools) he start freaking out again.
I don’t know what it is.

Do you mean that everything works fine as long as there’s nothing connected to the MIDI in?

Everything is ok as long as there isn’t a clock involved. When i put the tempo on external and don’t send a clock from my sequencer, only midi notes, it works fine. When i turn the midiclock on, the shruti starts to freak out. The same when I don’t connect midi to it and play a note, when the tempo is on external, everything is ok. But when I set a tempo, the shruti starts freaking out again.
And know I’m writing this I notice something else, the pots don’t have the complete range ie.when I want to select an oscilator for osc1 it only goes from none to noise, I can’t select the other waveforms. The range only goes from -24 to 7. And I can’t choose the XOR modulation. It looks like it doesn’t read out the complete range of the pots.

Could you please check the following:

  • the voltage on the right pin of each pots is 5V.
  • the supply voltage of the ATMega328p is 5V.
  • When all pots are set to their maximum value, the voltage on the <ANL line is 5V.

Back in the testroom. Thanks a lot for the help.
The right pin on each pot is only 3,21V
The +5v on the controllerpanel is 4,97V
The <ANL = 3,21V
The ATmega is 4,97V

Looks like we found the source of the problem! It looks like there’s a voltage drop somewhere between the pots and the +5V pin of the ribbon connector. It’s likely to be a bad solder point.

I think I screwed up the connection between 5V and the right pin on pot 4. Is it possible to go directly from the 5V point to the right pin?

Yes, if you look at the PCB image, there’s trace doing the connection… It might have been damaged (?) or worse, there’s a short somewhere. I really advise you to understand first what’s the cause of the problem - broken trace or short. Have you checked for continuity/resistance between the 5V input pin and the right pin of the pot?

I’ve put a wire in between 5v and the pot and everything is working fine What a nice little beast, thanks. And I’m looking forward to the sequencer!