Nov 242010

I’ve been obsessed with color organs lately, but most of my efforts have been pretty weak on the display side. Sure I can gin up a circuit or FFT code lickety-split, but I’ve been giving the LED end of the business short shrift.

This time I grabbed some ShiftBrite modules and I was able to fit six (I waste one MSGEQ7 channel) onto a breadboard. Some quick changes to my previous MSGEQ7 color organ code has me up and running. Here’s my latest effort:

 Posted by at 1:36 PM
Nov 142010
Flux is magic, but you’ve got to clean it up. Recently I was working on a instrumentation amplifier circuit and it just wasn’t working. Check the PCB. Check the schematic. Look for solder bridges. What’s going on? I was getting crazy results. Desolder the op-amp and put it on a little breakout board (SOIC) and plug it into a copy of the same circuit on a breadboard and it works fine. Try two different chips and it works fine! Put the chip back onto the PCB and it doesn’t work!

Anyhow, this was a protptype PCB with no soldermask and as a result, there was a lot of trace area in contact with the flux. I was using Kester 2331-ZX flux and it’s water soluble and VERY conductive. The resistance between two freshly fluxed pads on the breakout board below is about 100 KOhm. Without a solder mask, the resistance between adjacent pads can get really low. That’s just unacceptable for a precision circuit. Cleaning the board with isopropyl alcohol solved my problems and turned a non-functional heap of junk into a working instrument.

Finally, flux can be corrosive. The Kester 2331-ZX water soluble flux is great stuff, but besides being conductive, it’s also pretty corrosive. Check this out: I fluxed a few pads on this breakout board and let it sit for about a month. Now they are corroded and green.
Water soluble flux is nice, but you gotta clean your board! Some of the “no-clean” fluxes may not be as corrosive or conductive, but I’ve learned my lesson and clean every board.
Clean your boards!
 Posted by at 5:23 PM
Nov 132010

It’s a snowy afternoon, so why not fool around with some electronics? The MSGEQ7 chip is a seven-band audio spectrum analyzer chip. You just pulse a reset pin and then clock out seven analog values that correspond the spectral content in seven bands. It’s a lot faster than my Arduino FFT code.

Anyhow, here’s some video of the action on an analog scope: Instant gratification!

 Posted by at 4:38 PM