Archive for September, 2009

Coming up for air.

5 September 2009

About a week ago I decided I was going to make a dent in an old project that had been rattling around in my mind and in my parts boxes for years. So I turned off the phone, plugged in the soldering iron, and got started.

Last night I proudly displayed the results of my work at the monthly Weird Science ┬ámeeting (hosted by Bill Beaty at the Museum of Mysteries). It wasn’t finished, but it had a bunch of flashing lights.

It was my LED oscilloscope project. I’d thought of it years ago, and had bought a bunch of parts but could never get it built. It is installed in a Home Depot aluminum briefcase (toolbox) in the lid on a frame painfully created from old aluminum extrusions, an Office Depot purple plastic clip board, using, as I recall, both a back saw and a hack saw, plus appropriate files, old Penny’s drill motor and drill bits.

It draws a waveform on an 8 by 10 array of LEDs using a bar graph IC and a CMOS 4017 as a scanner. The system involves analog switch ICs, line selectors, and more yet to be put into the physical universe.

I needed some connectors to wrap it up so went to RePC on Friday morning. There I spent $7 on a few items, including an old 60-watt PA amp that I got because it had a beautiful brushed aluminum front panel. It was $3 because it didn’t work. I disassemled it into the sub-assemblies I wanted and then made the amp work on my +/- 24-volt supply (one of my most expensive purchases – about $30). It’s a switching supply. I try to stay away from 60-Hz transformers since I discovered switching supplies back in the 1970’s. Everyone uses them for everything now – I don’t know about audio equipment, though.