My MIDIpal looks great but I can’t get it to do anything so I have obviously screwed something up. All of the apps and parameters display fine but it doesn’t actually do anything. I’ve tried a few apps and there is no output. The LEDs do not light up and the Monitor app displays only a blank screen.

Any ideas on where I should start looking for problems?

Thanks.

From your description it is clear that the MIDI in is not working (the monitor app does not work).

I am not sure if the MIDI out works. Can you try the sequencer or ear training game apps – they should generate messages on the MIDI out. Does the MIDI out LED blinks? Do you get messages?

The most likely cause of the MIDI in and out simultaneously not working is a short between the UART pins on the MCU (they are adjacent). These are pin 30 and 31.

The LED colour isn’t important. But the standard is for the IN to be red and the OUT to be green. Is the IN really not working or is the LED simply not lighting up? it is possible the LED is the wrong way around.

If IN isn’t working then also check the diode is orientated correctly and the resistors are in the right place. An opto-isolator uses an LED internally to transmit to to a receiver. If you attenuate the signal going to the LED too much then it won’t light up enough.

it’s look like my problem…
i have not tried something yet but i will post the result soon has i do something…
Nico.

I’ll check that. I just measured resistance across the caps that I had de-soldered and then re-soldered into the correct places. I really don’t know much about this sort of thing but two of the caps give me .71 Kohms, and two are just an open circuit, no reading at all. Looks like I may have ruined C6 and C7.

All of the resistors around the optoisolator are fine.

I wonder if Olivier can mail another C6 and C7 over to Canada for me?

Randy

• You cannot read the value of a component while it is in circuit. A meter probes a component by sending current through it and measuring voltage (and vice-versa). When the part is in circuit, the current sent by the meter pours everywhere in the circuit, not just through the part under test.
• Capacitance is expressed in farads, not ohms.
• After a short time, a capacitor behaves like an open-circuit when subjected to a DC component.
• To measure capacitance, you need a special bit of equipment (multimeters rarely do it).
• If there’s something wrong with C6 and C7 the display, menus, etc. wouldn’t work.

If you have access to a scope, check pin 6 of the 6N138 – it should be at +3.3V at rest, with dips to 0 when there are 1s in the MIDI message. (you could also see that with some meters – +3.3V all the time, but short drops to lower values when some MIDI data is transiting).

I have only destroyed 2 parts over the past few years, and both were 6N138 – maybe the transistors in this chip are prone to electrostatic discharges? Could be worth replacing if nothing else works…

Oh, I checked pin 6, using pin 5 for ground, and it is 3.3 at rest, moving briefly when a note is pressed.

I may attempt this build this afternoon. If not, tomorrow.

I think I read that it’s a global reset? It’s in the manual.

So Randy, any words of wisdom for someone about to attempt this for the first time?

I read through the entire manual and didn’t see mention of SW2. Doh! The MIDI path starts at Roland A37 controller, through a Yamaha MJC8 patchbay, into the MIDIpal and then to the Shruthi. I’ll check some manuals, see if I can figure out who is sending the constant stream.

Titus, advice? Whatever I do, do the reverse! I keep forgetting the old “measure twice, cut once” advice.

Randy

Olivier’s advice to just use the quantity is the easiest and works fine.

Randy

What does SW1 do? I can’t find anything in the manual or the build page? How should it be set?

The SPDT slider switch?

How does it work?

@pichenettes – Thank you! I should have guessed that’s what it was.

I did it!

Took about two hours. I was very worried about the ATMega soldering but I guess it’s okay. You don’t need much solder…

The tweezers nabbed from the Internet badlands by qp turned out to be essential. I had no idea how terribly small this shit is.

Okay now to build the case, eat my reward candy, and see how it works.

We need a thread for the census of completed MidiPal kits…

Man you’re not kidding. They’re so small they look like something that could have fallen off of me somewhere. Little specks of whatever.

I am SO LUCKY I didn’t sneeze or fling one off of my desk because that would have been it. No extras. I need to get a staging dish or bowl or something to avoid that. Eventually my luck will run out.

I actually did blow a few across the workbench during a bit of sighing. I’m still trying to figure out why my Roland A37 controller is sending out some sort of constant stream of MIDI crap. I was hoping to give the pal a good thrashing tonight but my son grabbed the office/studio and I was stuck watching TV. Ouch!

Randy

Does it keep you from exhaling resistors all over the place? Or worse, inhaling?

What would you say they’re the size of? I was trying to describe them to my wife and was at a loss for words. Way smaller than a grain of rice. Slightly larger than a very small ant? A flake of dandruff? An eye booger?

How do you describe those impossibly small flakes of stuff?