prototyping & more testing

LEDs:

• I tried figuring out how to diffuse the LED light more. A friend sent me this link about a guy who made a color-changing tap light using 2 of each of red, green, & blue LEDs by reflecting them off a white surface first. He had a link in there to SuperBrightLEDs for getting ahold of several-thousand millicandella LEDs. From the pictures, it looks like just normal paper, but I tried that with very poor results. He said it was glossy, so perhaps, it's a piece of plastic or high-quality photo paper. I still haven't properly matched light intensities across the 3 colors, so that's part of my problem as well. I'll have to keep trying things I guess

TWI Communication:

• On Monday night, I tried to get the TWI (I2C) communication working between the microcontroller and the LED driver chip. It was a rather hacked-up job because I taped (yes, literally taped with scotch tape) the LED driver chip to a QSOP-DIP adapter chip that was then plugged into a prototyping breadboard. In addition to the standard wiring from the uC board, I also wired in 3 LED's just to test with. I grabbed the sample TWI code from Atmel's website (which puts the uC into master transmission mode, the mode I need to use) and changed a few minor things (device address and data payload) to try to get it to run.

• I plug everything in and get nothing... nada... great! Debug time! I remembered that the normal operation for the driver chip requires 2 bytes of data (address and value) to work properly, so I change the code to write out 2 bytes before closing the connection and try again. Same thing...

• I've got 6 LED's on the uC board at my disposal, so I use them for status indicators. I also double-check all the wiring, because it's an easy mistake and I've done it many, many times before. I also check the continuity between the driver chip and the board, since it's just taped to the adapter chip. Everything seems to be in order...

• ...

• ...

• Several hours later and several frustration levels higher, about all I'd been able to figure out is that I'm not getting an ACK signal back from the driver chip (actually, I'm getting a NotACK signal back, but I think that's what would happen if there was nothing on the TWI bus). All the wiring seemed to be correct and I'm pretty sure I got the address of the chip correct. Perhaps I'll have to try a dab of glue or something else on the driver chip to get it to hold to the adapter better. I ordered 40 driver chips from Maxim's website last week, but haven't heard anything from them other than the withdrawl of funds from my credit card, so I've only got the 2 engineering samples to test with. I've also got no other devices around that support TWI communication. Back to testing, I guess!