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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
Just thought I'd share a write-up I submitted last week for the 555 contest. Hope y'all have no trouble with the external URL (new territory for me). Next step is to learn how to format the document in HTML.
Anybody seen this general application before? (a 555 "VCO" with its control voltage modulated at a frequency similar to the free-running multivibrator frequency?) I discovered it independently, while playing with AC motors, but that does not imply that it's a novel application for an IC sold since 1971.
Got a rude reminder of an old lesson. At the last minute I changed my breadboard's bridge rectifier to a half-wave (single diode) rectifier, in the name of honest minimality and a simple "sine" modulation waveform. Left it running while I took pictures, uploaded them to PC, and wrote the document. Came back to find it dead. A multimeter and hammer soon revealed that the wallplug transformer's primary was open, because its thermal fuse had operated. I bet that's a consequence of using a half-wave rectifier with non-negligible DC load current, which flows in the primary winding and invites saturation. In the boxed version I'll use a center-tapped transformer and 2-diode rectifier, to preserve the sinusoidal modulation (which isn't strictly necessary) while minimizing DC magnetization.
[edit] Just realized that linking to project on another website is against the rules for Projects forum. Will expand the presentation right here, but might not have time for a few days. Sorry.
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60 Hz stroboscope for synch motors & 555 contest
