Dear friends,
I need help.
First, confession: My skills in electronics are rather poor.
Well, What I want to build is a times off delay for bathroom fan, frequently called extractor.
Originally, I had a fan with internal delay off control, but it went bad.
The fan is powered by 220V mains, through a relay from the 12V electronic circuit. The circuit is built around 4060 oscillator/counter.
The common wiring in Israel for these kinds of devices is a three prong outlet containing permanent phase and zero, plus switched additional phase (same phase), which is driven on when the lights are turned on, and turned off, accordingly when the lights are gone off (when the customer goes out).
Operation: as the lights in the bathroom switched on the fan goes on, and stays on as long as the lights are on. After switching the lights off, and after a preset duration (5-30 min), the fan turned off as well.
The main idea is that the controller is always hooked to mains supply, and the phase-on when light turned on, and then off provides the signal for clocking.
I tried on my own several configurations, with "beautiful" failures. For instance I thought of using logic "not" inverter on the delayed output (one-shot configuration) preset time, but the switched phase (bathroom lights) brings the reset to low, and resets the timer…
Many of you there have enough know-how and ingenious ideas as to how to work it out. Will you please enlighten me?
Thank you all in advance,
BTW: one important thing to remember. There is no momentary switch there to use for resetting. Only the three outlets: L (line) and 0, both permanent, and LT (switched line) witch turned the bathroom light, and delivers signal to the fan, and stayed on (latched) till tight turned off.
Yossi​

 

Ok you can use this timer circuit and use the PNP transistor output, this will put the fan-relay on when the light is on, and when the light is turned off, stay on until its times out select the pin for your delay pin 4 or 5.

You will need to use an opto coupler on the reset pin taken from the Switched live feed ,
this needs to pull the reset high to start it,


this will start the timer when the light is turned off, to keep the fan on when the light is on, the relay transistor needs to be kept pulled low, then when the light is turned off the timer takes over and keeps the fan on until time out.

opto

 

Or, you could simply install one of these UL / CSA approved bathroom fan timer switches...

http://www.marco.org/2012/05/06/bathroom-fan-timer-switches

 

Excellent option, gopher. Bookmark that page. This question comes up every couple of months on AAC.

 

Gopher,
My first thought exactly - particularly since the OP is describing a mains connected circuit and the OP admits poor skills. The thread could be closed for safety concerns.
dj

 

First, I'd like to thank Dodgydave, as well as the other members. djsfantasi raised a genuine concern about mains power and poor-skilled amateurs. I agree with him, and I thank him for being a serious watchdog. In this very case, though, as a scientist that works with ion-beams particle accelerator of 3.4 MeV on a daily basis, I think you can all relax. My poor skills are in electronic design, not in handling mega volts apparatus.
I thank also GopherT (did you like my name??)for the suggestion, although I'd rather build a simple circuit myself.
Dear Dodgydave, it will take me some time to contemplate your idea, and I'll discuss it here with friends. I believe I will need some more integration idea as to how to assemble the whole thing together. I did understand the basic functioning of the circuit, but I did nit understand how (why) it will turn on the fan at the moment of light on, and how the optocoupler will be connected in such a way, within the circuit, that its will reset the timer.
BTW: do you mean that after the cycle, when the timer gets to the preset time, its output will stay high, thus disabling the fan, till another lights turned on starts a cycle?