chipKIT® Development Platform

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Very strange 5v power problem

Created Mon, 23 Jan 2012 13:26:43 +0000 by BoH_Havoc


Mon, 23 Jan 2012 13:26:43 +0000

Hi, i finally had the time to toy around with my max32 and after some basic tinkering tried to run my work in progress 16 channel synthesizer with MIDI in/out on the max32. Turned out i just had to change the timer stuff from atmega to pic32 and everything was working. Except that i didn't get any sound. ;)

After some trial and error i found out that my MIDI input wasn't working, there was no serial data at all from the midi in. So i did try to use one of the other serial pins. Still no luck.

After 8-10 hours of frustration i finally got it to work ... by using my old arduino's 5v out for the midi circuit! (It's not 100% working due to grounding problems between the max32 and arduino...midi is a bit bitchy about that ;) )

I'm using something similar to this as my midi in, except that i'm using an IL-74 instead of the 6N138 tigoe. net/pcomp/img/midi-schem.jpg (remove the space in there...can't post a direct pic link because of that -> "Your post looks too spamy for a new user, please remove off-site URLs.")

Ok so i thought my usb cable might be broken or something like that. Tried 3 others, still not working. I then used an external 9v power luck.

Finally i hooked up a volt meter to 5v and gnd pin of the max32...and got 5v!?

Why, oh why are there 5v on the 5v pin but it's not working? I really have NO idea what's going on here. :lol:

Any ideas?


Mon, 23 Jan 2012 15:36:22 +0000

when I put an oscilloscope on an USB powered uno32 from a laptop I had some interferences. when I disconnected the laptop from the mains and ran it out of battery the interferences were gone. maybe you have a similar problem


Mon, 23 Jan 2012 16:05:01 +0000

Thanks slayer1991, that was it! :)

I have it working now using the USB power supply from my Samsung Tablet.

But changing the USB cable between PC and power supply each time i want to upload some code really is a pain. Also debugging via Serial Monitor is no longer possible.

The Arduino Duemilanove can run my synthcode and midi input without an external USB power supply using the same USB slot on my laptop as the max32 is now using.

What has to be done to get it working with a max32? (Disconnecting the power supply from my laptop didn't help.)


Mon, 23 Jan 2012 21:48:21 +0000

I think it has something to do with how the chipKit takes power from USB. I noticed that I had random values bigger than 160 on analogRead an unconnected pin. After unplugging the laptop it went down to 20!


Sun, 27 May 2012 15:56:46 +0000

Just for future reference and if others have the same problem:

Adding a 100Ohm resistor in between the uno32/max32 +5v ouput and the midi interface +5v input fixed it for me. I have no idea why, though ;)