Nifty very low frequency / low power oscillator. - Page 1
Forum section: electronics / projects

author: AnalogueLove1867
author_rank: Regular Contributor
timestamp: October 30, 2021, 05:26:27 pm
content: Hello peoplesHad a friend over who was asking about electric oscillators since he's a former pure math uni wiz.My scope isn't at home, so quickly improvised this on the spot to demonstrate a visible slow oscillation.He was surprised and so was I.It seems perfectly periodic/regular. You can get the frequency down to 0.3HZ and past 50HZ ( perceived as a constant light ).The LED starts completely off, slowly ramping up to a bright pulse like a sawtooth wave.You can tell that there are two frequencies. One high frequency (kHZ / MHZ?) that is being amplitude modulated very slowly at a visible frequency.The periodicity of the flashing isn't affected by a close proximity charged PVC pipe.Disconnecting all potential sources of mains noise doesn't affect anything.That's all, stupid first post.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 30, 2021, 08:54:51 pm
content: What's the purpose of R1?

author: AnalogueLove1867
author_rank: Regular Contributor
timestamp: October 30, 2021, 10:23:47 pm
content: Without R1 the LED fails to display the controllable regular/periodic slow ramp ups from completely off that end in bright pulses.Replacing R1 with just a wire connection to the negative terminal causes the LED to stay feebly lit the entire time with some random non-periodic faint flickering.Removing R1 and the wire connection from the negative terminal results in no light ever coming out the LED.The five transistors wired together in a Darlington quintuplet configuration are extremely sensitive to microscopic DC currents and background AC fields applied to the base of Q5,ONLY when the Negative terminal has direct access to the Emitter of Q1 and the collectors of all transistors are slightly lowered in positive voltage due to a leakage current to the negative terminal.A connection to ground also works. This ensures that across every transistor the optimum potential difference between the collectors and emitters is maintained for maximum amplification.Oscillations can make their way through R2 and C1 to the Collectors of the transistors which further contributes to feedback.A direct connection of the transistor collectors to the positive terminal and this Darlington configuration fails to amplify.With these particular transistors a Darlington configuration with only two transistors will do just fine with a direct positive terminal collector connection.Any more than two transistors and it fails to amplify in practice without this particular setup.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 30, 2021, 11:01:35 pm
content: As drawn, R1 just shunts across the supply and should theoretically have no effect on the oscillator. Assuming the supply is a battery, might there be some ionic nonlinear weirdness that needs a (small) minimal load to not disturb the circuit?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 30, 2021, 11:30:23 pm
content: It's a very strange arrangement, it looks kinda like a squegging oscillator to me. R1 would be what kickstarts it when the battery is inserted.

author: AnalogueLove1867
author_rank: Regular Contributor
timestamp: October 31, 2021, 12:06:05 am
content: In practice it is a light and day situation.Originally put it together with a good regulated lab power supply............It does also work with batteries.Guessing the key lies in the negative terminal current being shared amongst the emitters in seriesand the positive terminal having to supply current to five collectors in parallel.So when a signal hits base of Q5, If a single transistor completely saturates before the others it eats up the available positive terminal current supply.This restricts the current available to the other transistor collectors and so reduces the amplification provided by the others and thusthe total amplification of the Darlington configuration.When all transistor collectors consume roughly similar amounts of current a far greater amplification is achieved.The resistor shunt has a high enough value that it doesn't significantly reduce the potential differences between the collectors/emitters.BUT it does significantly reduce the available current to the collectors thus preventing any one transistor from having a saturation runaway.That is the best explanation I can give.

author: AnalogueLove1867
author_rank: Regular Contributor
timestamp: October 31, 2021, 12:52:04 am
content: Thanks, looked up the meaning of a squegging oscillator. That's definitely what it is.Was wondering if it had a standard name like every other circuit. Cheers.

author: coppercone2
author_rank: Super Contributor
timestamp: October 31, 2021, 04:28:40 pm
content: i kind of want to build it, whats the transformer used?like a iron core from a linear supply or what. have so many 3904 and other cheap transistors that this is almost no effort or cost

author: Renate
author_rank: Super Contributor
timestamp: October 31, 2021, 04:37:27 pm
content: https://en.wikipedia.org/wiki/Squegging

author: AnalogueLove1867
author_rank: Regular Contributor
timestamp: October 31, 2021, 07:03:43 pm
content: Here ya goWriting on the transformer isTÜV RheinfandNFK-10 ta=50⁰CPRI:240V-50HZ 12VA ROTSEC:12V-50HZ 10VA SCHWARZAlso info for the transistor used.

author: AnalogueLove1867
author_rank: Regular Contributor
timestamp: November 03, 2021, 02:46:46 am
content: A similar circuit modified to behave in a completely different way!Instead of a pulsing light, you have a continuous light that is turned on and offby lightly touching resistive contact switches.Touching the "on" contact again when already on results in no change as does touching the"off" contact when the light is already off.This circuit only needs to be modified slightly to accommodate a true capacitive switching.Even a distant capacitive switching of 5cm air distance between finger & sensor IS possible.However, it is ultra sensitive to AC noise and static. It is impossible to use without shielding.The air-conditioner, washing machine or ceiling lights in other parts of the house will remotelyswitch the light on and off without shielding. The 100MΩ resistor in this case was a small 1cmX1cmpiece of cardboard held with alligator clips.It works very well, but it's a tough build to get right. So you've been warned!.