I received a Google Alert and watched Jonny Davro’s Diode Oscillator running from a AA cell and putting out light when connected to, among other coils, a Slinky spring. I thought that I should have a go at this odd circuit.
I assembled it as he showed in the schematic. I used the same BC560C for the NPN and a 2N3906 for the PNP; both were new, fresh out of the package. The diode was a real 4148 or 1N4148. The LED was a white 5mm, right out of the package. The coil was a 1/4 inch (6mm) core bifilar wound with 8 turns of 30 AWG, and measured 200 microhenrys per winding. I tried the single winding and also both windings connected in series. I also tried a 2N4403 for the PNP transistor.
In all cases, when I connected and disconnected the power supply lead, I saw a feeble flash from the LED, but other than that, nothing. The current when connected was about 20 milliamps for the 2N3906 and 50 mA for the 2N4403. I varied the voltage above and below the 1.5V and the current changed as expected, but nothing from the LED. In the picture I show the LED connected across the coil, but I tried it both ways with the same results.
I suspect that the reason Davro’s circuit oscillates is because he uses a proto board and long clip leads and the stray capacitance of the board and wiring causes the circuit to oscillate. In my case, there is almost no stray capacitance, so it will not oscillate. This is just another one of those experiments where results are influenced by outside factors both unintended and unaccounted for. There’s a lesson to be learned here, I think.
Back to experimenting…