Thursday, April 23, 2009

Slow Progress



Not a lot of progress this week. All I managed to do was attach my repair wires to fix the reversed power and output on the TI OPA380A chips. I haven't even had a chance to test it. With any luck I did not smoke the chips.

It took me around two or three hours of futzing to put the wires on. Just a bit faster than I could remake the whole board. Of course, if I smoked the chips, I'll be remaking it any way.

On another note I happened to run across a really neat piece of electronics art. I really dig the air-wire scheme it has going on. I can see using the technique in a trophy design.




Wednesday, April 15, 2009

Blunderifc

Well it seems I made another blunder quite some time ago and have only now just seen it. I finally got around to firing up Uno's sensor board for testing. The Transimpedance Amplifiers immediately got hot. After poking around a bit I discovered that the library component that I created for DipTrace has the pins in descending order.. on both side of the SOIC chip. Doh. I got lucky, two of the four pins are N/C on the bad side, but the output and the Vcc got swapped.



You can see where I've begun cutting the traces on one of the four amplifiers. I hate to make this board even more ugly than it is, but if I didn't fry the chips its still a good bit less time to cut traces and solder jumpers than to remake the whole board, even with my new solder paster skills.

Wednesday, April 01, 2009

Side Project: Necklace



My wife had been after me for a while to make her a necklace with a copper pattern. At last I got around to it this past week. I learned a few new things and it was also pretty good solder paste practice.

The necklace itself is four jewel style LEDs that run off an ATtiny13 and are powered by a CR2032 coin cell battery. The program starts the Timer in Normal Mode with a 1024 clock divisor and then goes to sleep. When it wakes up on the timer overflow it increments a variable and goes back to sleep. Once the variable exceeds a threshold the MCU makes the LEDs blink around a bit, resets the variable and goes to sleep once more. The ATtiny13 is clocked at 600kHz and the variable threshold is calibrated to make the LEDs run about once an hour.

It had been my intent to clock the MCU at 128kHz to save the extra power. The first time I tried to set up that clock I had AVR Studio set to the the wrong MCU type. I bricked the MCU. Doh! As I discovered however, with an extra person applying leverage with an exacto knife, you can use an embossing gun to pop the chip off with little to no damage to the PCB.

Having mounted a new chip I tried to set up the clock once more. After the clock was set to 128kHz I could not talk to the chip any more. It seems that little note about making sure the ISP clock is less than 1/4 the MCU clock is for real. My ISP's clock speed is adjustable, but I learned at that moment that 56k was as low as it would go. Another MCU bricked. Doh!

The third chip was the charm because I decided that I could live with 600kHz. The docs say that in sleep mode at 1MHz the chip draws 24uA. I was able to turn off a couple extra peripherals and am running lower than 1Mhz so hopefully I'm doing better than 24uA and will get a decent life out of my coin cell. However, even with the 1024 divisor the chip has to wake up more often than twice a second to increment the variable. I guess we'll see what the ultimate battery life really is.