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need time delay for AC circuit

need time delay for AC circuit

need time delay for AC circuit


I'm pretty sure what I need is the equivalent of a single shot timer relay. What I want to do is control the "ding dong" sound from a door bell. It operates on 16VAC. In normal operation when the doorbell button is pushed a plunger is pulled into a solenoid and strikes the "ding" bar. When the button is released, the solenoid releases the plunger and a spring pushes it back to hit the "dong" bar.

I want to make it so the solenoid is energized for a set length of time regardless of how long the button is held. The exact length of time is not important (I assume it will be easily adjusted by changing resistance or something) but for now let's figure a 1 second hold time.

Separately, I'd like to also "lock out" the button from being able to reactivate the solenoid for a period of about 10 seconds. Anyone who's had a 3 year old ringing a doorbell will understand the value of this. This feature will probably be on a switch to have it enabled or not.

I'd like to do it with parts I'd solder myself. I'm confident both functions can be done with a simple R-C type circuits but I need help figuring it out.


RE: need time delay for AC circuit

Simple RC circuits will be confused by the AC.
Conversely, the AC can serve as a clock for digital timer circuits.
I get the impression that some industrial time delays are mechanical.
There are a lot of choices, but the fastest, cheapest one, is the one on the shelf.

Search for 'AC time delay relays', and see what you find.
For instance, a relay designed for 24VAC _might_ work on your 16VAC. Read the spec sheet, or just buy and try.

OR, and you should consider this mostly for educational value, buy an Arduino and appropriate 'shields' to interface with your world. It will cost a little more than a simple time delay relay, but is capable of arbitrarily complex behaviors.

Do not even think about buying bare microcontrollers and associated surface mount components and soldering them together yourself. Doing so requires tiny soldering irons, strong lighting, magnification, ... and you will still burn your fingers and always worry if you did it right.

Mike Halloran
Pembroke Pines, FL, USA

RE: need time delay for AC circuit

I hate to say it but I have given up discrete design. I buy those Arduino 328 nano's with USB port for $2.50 shipped and it is like a ready made breadboard I can tack a transistor and resistor to. I worked for a company that made plug in one shots, on delays, etc and I have boxes of units that failed off production. Easy to fix, but I should just toss them. That world seems ages ago. That said it seems anything you could want is on ebay. Sometimes I'll spend an hour just doing random search of a vendors items and find things I never thought existed for cheap.

RE: need time delay for AC circuit

I always hold the button in so it 'dings' until the door is opened then I release the button for the "dong".

Keith Cress
kcress - http://www.flaminsystems.com

RE: need time delay for AC circuit

Thanks for the replies. I was really hoping to have a little project over the weekend with a pile of stuff from Surplus Gizmos. Which I may still do, just not in the way I had thought.

RE: need time delay for AC circuit

The old-fashioned way to do this would be to use a a pneumatic timing relay and tap one of the timed contacts off the coil supply to break at a defined period after coil energiseation. You get a pulse of defined length. Look for 'Agastat' or similar devices on the surplus market.

RE: need time delay for AC circuit

555 timer.

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