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| LED oscillation behavior with 'BAD' or tenuous contacts |
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| RJSV:
I noticed odd back and forth oscillations, between the apparent brightness with two LEDs connected in parallel, and wnen there is a tenuous connection created by using two tiny wires that barely touch. The experimental rig is simply using two batteries, for 3 volts, and a common resister of 1 K ohms. For the switch, I mounted two stranded wires facing each other, and removed all but one or two of the delicate strands, for testing. I'm assuming there are SURFACE OXIDATION effects, and possibly even some 'micro-sparking' that resembles the spark gaps of the old radio-telegraph days. Watching the LED pair flicker, I notice one LED will dominate, sometimes completely, and with this state of affairs flipping (so the other LED dominates) over about 40 seconds. I need help on the theory here. My thoughts are that the mechanical 'rubbing' and contact interruptions are creating switching frequencies up to maybe 10 KHZ, but my scope is showing some pretty nasty and fast 'hash', perhaps much higher; maybe RF content up to 10 MHZ ! So my theory is that there is sparking, on a microscopic scale, causing an effective RF transmission circuit similar to old radio telegraph circuits of 1890... Now, why the LED pair trade off in blinking, that's an interesting question. My scope showed about 50 milliVolts, of AC. The red LED pair operated at 1.7 volts, while a single LED operated at 1.8 volts. This is because the two LEDs interact, due to sharing the 1 Kohm load resister. |
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