I have been having trouble with no MIDI signal being received since building my shruthi in December. I have continuity between pin 6 of the optocoupler and pin 14 of the MCU but can see no deflection on my meter when MIDI data is sent. MIDI set up tested and working perfectly. Please can somebody help? Any ideas greatly appreciated.
Is pin 5 of the optocoupler continuous with ground? Pin 8 of the optocoupler +5V?
Yes. Pin 8 at +4.98V and pin 5 is continuous with ground.
Maybe you could post a photo of your board?
I’ll do that.
If these are too low quality I’ll try to get a better camera.
Maybe these are better?
I don’t see how this could be related to your problem (in theory, this should cause problems with the MIDI out) - but the two resistors next to the optocoupler are swapped.
They are? Ok, I’ll get that sorted and see what happens.
I see 10k and 220 at the right of the optocoupler. Should be 220 first and then 10k.
Well spotted. I’ll swap them over as soon as I can.
Swapped those two resistors. But as expected it hasn’t changed my MIDI in issue. Any further testing I can do? Really stuck on this one.
Maybe you could try another 6N137.
I guess so. I have already replaced that part once though. Could it be the MCU maybe?
Remove the MCU.
Check the signal at pin 6 of the 6N137 while it receives MIDI data. If pin 6 is stuck at +5V, the problem is not due to the MCU.
Tried this and it is still stuck. Not the MCU. I will try another 6N137 then and see what happens.
Tried another 6N137 and still no MIDI in. What should I try next?
Maybe we should have started by the basic: are you sure about your cable? Is it inserted in the right connector?
Sure is. It’s running another synth right now. Have tried multiple cables, different controller keyboards, my Akai MPC, all of which work fine with each other.
Plug a MIDI cable into the Shruthi MIDI in. Check the resistance between:
- pin 4 of the DIN connector at the other end and pin 2 of the optocoupler.
- pin 4 of the DIN connector at the other end and pin 3 of the optocoupler.
- pin 5 of the DIN connector at the other end and pin 2 of the optocoupler.
- pin 5 of the DIN connector at the other end and pin 3 of the optocoupler.
Post your results here.