I've recently posted a number of projects for GRAINS. But I may need to yank many of them because I often have to set two pins, namely IN3 and Audio In, to OUTPUT. These are normally analog ins.
The problem is that shorting an output pin to ground, or to Vcc, or to another output pin, will destroy it because it will pull more than 40ma.
I presume the two dedicated output pins (Audio Out, Digital Out) have protection -- like a simple resistor in series. What I do not know is if other pins do. I know that if you change In1 or In2 (which go through the pots) to OUTPUT, bad things happen. It seems that In3 and Audio In work fine as outputs attached to, say, drums or other triggers. But I am worried that some user may attach them to Ground on Master I/O or to +5V on 4ATT-MIX, or to the Braedboard, and if they're not protected...
Does anyone know if In3 and Audio In are protected and safe to use as outputs?
I have examined the GRAINS and can safely say that I have absolutely no idea. The traces in question don't appear to be on the outside layers. So I think Tangible Waves is the only one who can answer this question. :-(
I believe the In3 and AudioIn are A3/PC3 and A4/PC4 respectively, which according to Atmel's description sheet (page 12) are the second and third pins from the far right respectively on the top edge of the TQFP package chip. My multimeter says that the resistance from the pins to the sockets (module unplugged) appears to be about 4.5 to 4.7 kohms. That's a good sign right? I think that you supposedly just need a 150 ohm resistor to limit the current on the output pin?