Momentary switch - press once needs to give 5 seconds of power

Question

Electronics is not my forte, so bear with me on the nomenclature.

Backstory

We have an old house and my wife bought me some old butler bells to get going as our door bell.

I found a motor which turns a handle to throw the bell left and right and when it's on, it needs to be on for a few seconds for the momentum to build up and ring properly.

Now, I can have a door bell button and if I hold it on for 4-5 seconds, the bell rings nicely. However, I have this old door bell puller. I have a momentary switch installed at the back of it so, at rest, the switch is pressed and no power flows (momentary off??). When you pull the handle, the switch is open and power flows while you pull it. This works, but I've found most people when they pull it, they just let it go. So I want to do something that allows power to flow for a minimum of 5 seconds, whether I pull it once and let it go or for longer. Obviously if I pull and hold for 10 seconds, it should ring for 10 seconds.

Question

What can I add to a momentary off switch, to allow it to run for a minimum of 5 seconds on one press/release?

Thank you.

Update from the comments. This is all about 12v from a normal doorbell transformer.

Answer 1

There are 2 approaches possible here:

1. You grab a bunch of capacitors, resistors and transistors and start messing around to make a timer circuit. This is the most fun (according to the users of this board) and the most educational, but it is also the most likely to fail. This solution is also super cheap, if you don't value your time much.

2. You grab an off the shelf component that has solved this issue thousands of times in the field. I personally like the Omron H3DK series timer relays. They are robust and intuitive to use.

Answer 2

I would purchase a cycle timer, with the button pushed the relay pulls in for a time period you select sometimes with switches , or dials . I have some that work on ac-dc120 -240v others that work on 12-36v ac or dc, both have isolated relay contacts so you could operate a high voltage device with a standard low voltage, (doorbell signal circuit) these are made by Omron (h3CR-A8) Allen Bradley, automation direct (ms4sm-ap-arc).

Of the brands I have handy those are 100-240v, 24v ac-dc MS4SM-CE-ADC. This with the appropriate socket can be easily wired and you can dial the ringer for whatever length you want if you want 5 seconds for a bump of the switch set it for seconds and turn the dial to 5.

I use these for all kinds of things. If the 100-240v model is used it needs to be in an enclosed project box. If the 24v one is used I do like to have them in a box but the rules are quite lax in that case.

Answer 3

I'd use a modern time delay relay for your "one shot"

While it's possible to fabricobble a one-shot function out of components rather readily in this day and age, if you want a known-reliable result, though, you're best off with a premade, multifunction time delay relay. I would use the Macromatic TE-8816U here; it's inexpensive (~$40 as of the time of this writing), can be mounted in a variety of enclosures as it uses standard DIN rail mounting, and is fully UL 508 listed for being field-applied-and-wired. One note is that you'll have to run a 3-wire control cable from the switch to the relay with this part, as it uses a dry-contact trigger in one-shot mode.