While waiting for more OPAs and other asst. opamps to arrive, I got bored. I bought some toys. I got some LM3915 LED VU driver ICs and a few 10-segment low mA LEDs. http://www.national.com/pf/LM/LM3915.html
http://www.qtopto.com/displays/d0402m3.pl5?MV5C164&MV5y164.pdf&191
Wiring them up is pretty simple normally, all + LEDs wire to voltage and all - wire to individual pins on the 3915s. By default the ICs are set for line level audio, just add the resistor of your choice to pick the current for the LEDs and you're done. I wired them so all 20 LEDs lit plus both ICs takes 12mA.
Then I discovered the LEDs I got were BACKWARDS! The anode/cathode config made the array from 1-10 being amber/red/green. So I had to reverse hook them or send them back. I braved the iron and did it myself. Talk about soldering practice! (stripping and tinning 20 tiny wires was the hard part actually)
I will never use perfboard again. Well, at least not the kind without pads. This stuff sucks to solder on, if you make a good electrical connection the component might still be loose because there's nothing to make it stick to the board. I ended up making it structurally sound by globbing up solder on the leads. Just like those example photos of how NOT to solder.
Luckily I had some 20-pin sockets from another experiment I'm doing (digital pots - more later) because the channel for where the control board would mount wouldn't have made the LEDs even close to flush with the panel. The socket was the perfect height though, the arrays ended up being 1/16" from the front of the faceplate.
After cutting out a 1x1" hole in the faceplate carefully (measure twice cut once) I got some smoked gray transparent sticky film from an arts & crafts store. 1 yard of 3' wide was $1.29. It looks just like film for tinting car windows. It sticks once and that's it so position carefully! I got it right on the 2nd try and trimmed the edges. Damn, that looks sweet! Total cost, $12.00
I only ran into one problem wiring it up. The volume pot makes the signal drop even though it's spliced into the line in before the pot. Ugh. Knowing that a diode would fix it, I tried a few different ones and stuck with 4002s. But THEN the diode is dropping voltage and the LEDs are lighting lower. I know I could have solved it mathmatically but ole newbie Apheared did the brute force method - I stuck in my test tone CD, hooked up the voltage reference/bias pin via a pot, and "calibrated" it. Then measured the pot and stuck in the nearest value resistor. It's probably not accurate at all... but hey, it's just for "ooh aah" factor anyways :)
posted 07-30-2000 07:59 AM CST (US) 
