Simplest oscillators for DC

[Belfior]

This would give at least kilohertz

https://www.youtube.com/watch?v=I24nDi_q-EU

reed switch that stays open until the cap is charged and then it dumps, when the current stops flowing

[Bob Smith]

How fast can we switch with a relay so that it won't break in few hours?

The simplest solution so far has been a BJT in reverse avalance so the base is hanging. I think it needs something inductive on the secondary side and not just an LED to work though.

I have also seen 2 mosfets connected to a battery and switching. Can't find the video anymore

What I've found with the reverse wired relays is that they self-oscillate at a fairly low frequency. That can be played with a bit with resistors. The smaller relays seem to run faster. But as you say, wear and tear seems to have its effect on them. I believe the internal arcing also wears away at the contacts after a while, at least from what I've seen when running them for extended lengths of time. The trick might be to run the DPDT relay at the lowest possible power.  I've run them off small (5w?) solar panels.

[Bob Smith]

Question:
Is a tank circuit (simple L-C) an oscillator if the cap is discharging  and the inductor is powered by ambient energy?
Bob

[Belfior]

Question:
Is a tank circuit (simple L-C) an oscillator if the cap is discharging  and the inductor is powered by ambient energy?
Bob

Well it must be, but how much ambient can you get?

[Bob Smith]

Quote from: Bob Smith on January 23, 2019, 06:58:31 PMQuestion:
Is a tank circuit (simple L-C) an oscillator if the cap is discharging  and the inductor is powered by ambient energy?
Bob
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Well it must be, but how much ambient can you get?

Probably not more than a few millivolts. But with the low millivolts, to get a tank circuit, wires can be twisted around each other in place of a capacitor, for very low pico farad capacitance:
https://www.youtube.com/watch?v=v1wWL6TGWOE
Once an oscillating LC circuit is established, other things can be done.
Bob