Would it be possible to build a timer circuit, using AC signals only ? - Page 1
Forum section: electronics / beginners

author: nipil
author_rank: Contributor
timestamp: October 01, 2025, 07:10:33 pm
content: I just bought a din-rail mounted YCT8-M2 timer relay module on aliexpress, then i wondered :As opposed to embedding a DC sub-circuit in it, would it be possible to build "some kind" of delay circuit, using AC signals only (whatever voltage and current) ?My intuition tells me that no, as the signal keep changing, i do not "see" a way to "accumulate" something...Then i thought that there could be a way to use the phase shift between voltage and current, and maybe increasing the phase angle over time, finally triggering when phases were at a specific angle ?I really do not know, if it would be possible, and if so, how ?! A variable capacitor or variable inductance ? How to make it vary ?By the way, this is just a thought experiment, for which i could not think of anything viable.So i'm sumbitting this existential question to the sharp minds of this forumThanks in advance for any thought on thisNicolas

author: MrAl
author_rank: Super Contributor
timestamp: October 01, 2025, 07:17:26 pm
content: Quote from: nipil on October 01, 2025, 07:10:33 pmHi,I can't look that up right now but in the past they would use AC signals from the mains line (50 or 60Hz) to time alarm clocks and other clocks. It would simply count the cycles and display the time in digital format using 7 segment LED displays for the numbers, like "10:34" with a single LED for PM.

author: anvoice
author_rank: Frequent Contributor
timestamp: October 01, 2025, 08:17:23 pm
content: If your goal is simply to accumulate charge on a capacitor, a single diode will easily suffice (chop off part of the waveform).

author: TimFox
author_rank: Super Contributor
timestamp: October 01, 2025, 09:51:08 pm
content: Many fancy DIN-rail industrial control modules are powered from 50/60 Hz AC, but use DC digital circuits internally powered from an internal rectifier.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 01, 2025, 11:10:40 pm
content: As an attempt to offer something that hasn't been mentioned already, I suppose you could use a very low frequency alternating current, with a period at least four times longer than the time interval you require. Then you could simply start timing at the zero crossing, and use a level-sensitive trigger to stop the timing at whatever point on the rising voltage curve you require.It's rubbish, of course, but you did ask! 😄Not really rubbish, because this type of timer is used as a domestic lamp dimmer.

author: Analog Kid
author_rank: Super Contributor
timestamp: October 02, 2025, 12:18:45 am
content: Quote from: themadhippy on October 02, 2025, 12:12:37 amThat looks like, what? the sequence relay for a washing machine?

author: themadhippy
author_rank: Super Contributor
timestamp: October 02, 2025, 12:25:38 am
content: Quoteone of many uses, chuck power to the motor and there'll be a delay,that often can be easily changed ,before the switches change state,most used a synchronous motor so timing was pretty good

author: PGPG
author_rank: Frequent Contributor
timestamp: October 02, 2025, 12:32:27 am
content: Quote from: nipil on October 01, 2025, 07:10:33 pmDo you mean without any DC in circuit at all?

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: October 02, 2025, 01:19:05 am
content: It is called an electromechanical timer.

author: temperance
author_rank: Super Contributor
timestamp: October 02, 2025, 03:09:24 am
content: Heat something and use the pressure, steam,... as a trigger.

author: nipil
author_rank: Contributor
timestamp: October 02, 2025, 06:31:53 am
content: Quote from: TimFox on October 01, 2025, 09:51:08 pmThat is exactly what i bought, but i wanted to know if a "timer" could be done with "dumb" componentsQuote from: UnijunctionTransistor on October 02, 2025, 01:19:05 amGreat idea, i did not know of this.Although a non electrical one, except for the electricity powering the motorCould you provide any sense of the longevity of such devices ?Quote from: PGPG on October 02, 2025, 12:32:27 amThat was the idea, and by that i do not mean (only alternative voltage) but no "electronics"ie, no microcontroller, transistors, comparators, and stuff like thatof course AC-compatible devices (R,L,C,triacs, relays, etc) could be usedQuote from: anvoice on October 01, 2025, 08:17:23 pmThis one could work for the first "part" of the problem : by rectifying, you could load a capacitor voltage using an RC circuitBut then, how would you trigger the action (ie. compare with a threshold) ... without a "comparator" (or anything similar) ?

author: MrAl
author_rank: Super Contributor
timestamp: October 02, 2025, 07:05:26 am
content: Quote from: nipil on October 02, 2025, 06:31:53 amHi,It sounds like you are looking for the simplest possible circuit. In this case you might use a relay with an RC network powered by a battery or rectified AC. As the capacitor charges, eventually the relay contacts close (or open).I don't think you can get any simpler than that, but it depends how long you want the timer period to last. Is it seconds, minutes, hours, days, etc. This will play a huge role in what kind of circuit you can get away with. You should specify what time period(s) you want.

author: indeterminate
author_rank: Regular Contributor
timestamp: October 02, 2025, 07:21:15 am
content: Thermal time delay relayhttps://lampes-et-tubes.info/rs/rs083b.jpghttps://lampes-et-tubes.info/rs/rs061a.jpgThere where quite a few vacuum tube timer relays available back in the day

author: PGPG
author_rank: Frequent Contributor
timestamp: October 02, 2025, 08:26:06 am
content: Quote from: nipil on October 02, 2025, 06:31:53 amPeople built clocks based on dripping water. There was also something about ancient times where a priest would light a fire, and after a while, the temple doors would open 'on their own'.

author: Ian.M
author_rank: Super Contributor
timestamp: October 02, 2025, 08:38:08 am
content: Its very much a technology path not taken, but the same AC excited thin film magnetic bubble technology used for bubble memory could also be used to implement all logic functions, and theoretically a turing complete computer. Readout of the magnetic output state without using DC in the read amplifier would be challenging but I believe not impossible. That would give you not just a simple timer, but full PLC like functionality. And yes, all without junction or field effect semiconductor electronics, or any moving parts.

author: nipil
author_rank: Contributor
timestamp: October 03, 2025, 01:25:15 pm
content: Quote from: indeterminate on October 02, 2025, 07:21:15 amDo you have any reference for the "lamps" you posted ? this is cool ! (pun not intended)On the same note, there seem to be something related to heaters, which would do kind of the same thing as your "lamps"https://www.warrengv.com/sites/default/files/LT%26GT-Series-AirflowSensorsV2.pdfVery interesting.Quote from: Ian.M on October 02, 2025, 08:38:08 amWould you happen to have more information about this ?Googling the terms seem ot lead to research papers only... that's what you name "technology path not taken" (yet ?)Quote from: MrAl on October 02, 2025, 07:05:26 amAs for the duration, i do not have anything in mind, that was all just fishing for ideas, a thought experiment.As for your proposal, that would indeed fit the "though description" : few components and simple "non-electronics", and aside from a diode, fully AC.I just thought that at the "coil triggering voltage", there might be some bouncing around, depending on the voltage rising rate, though...So using a "latching relay" (even if the return stroke would have to be manual, etc) would solve the bouncing problem : once triggered, it would stay.Thank you all for your feedback, i would have not guessed there were so many ways to make an "analog" timer (without "electronics") !

author: Analog Kid
author_rank: Super Contributor
timestamp: October 03, 2025, 10:30:39 pm
content: Quote from: nipil on October 03, 2025, 01:25:15 pmWellll, it would help a lot to at least give us a ballpark figure.Milliseconds versus minutes would call for quite different solutions here.Can you give us at least a guess as to the timing interval?

author: nipil
author_rank: Contributor
timestamp: October 05, 2025, 05:44:06 am
content: Quote from: Analog Kid on October 03, 2025, 10:30:39 pmI am sorry I did not provide an adequate answer the first timeI was thinking either- in the order of 1-10 minutes for something like heaters- in the order of 0-5 seconds for something like motors

author: MariuszD
author_rank: Regular Contributor
timestamp: October 05, 2025, 09:26:38 am
content: I found an example on our forum.https://www.eevblog.com/forum/projects/solid-state-triac-based-inrush-current-limiting-for-inductive-load/