Cheapest timer for a 5w light bulb for 3-5 min

[LesterPester]

Ok, I know, I know. I used to teach this stuff. But three strokes has erased some of my gray matter and I have to still work a little bit longer. After a two year period of no money I finally have a small design job and I finish the housing and get down to the electronics and run into a brick wall. Here is what it is. I have a request for a simple night light with a 5 watt light bulb, and a normal light sensor in it but the client wants to have a timer to turn the light off after 3-4 minutes. Later he wants to be able to offer the same system with a motion detector circuit in it. Before my last stroke of the three of August of last year I used to be on this site a lot. If you can, please help me. I must say it does fell good to be back.

Sincerely yours,
Leslie H. Howell

 

[Myndex]

1) Sorry for the stroke.

2) In your "normal light sensor" circuit, add a 555 timer, set for 3 to 4 minute duty cycle.


Andy

 

[MacGyverS2000]

555 or a PIC (like the ones in the SOT-23 packages).


Dan
Owner

http://www.Hi-TecDesigns.com

 

[melone]

Would a self-timing relay from Omron work?

 

[sdmays]

LesterPester mentioned "night light". That suggests to me the product is being powered by 120VAC. If the product is being powered by 120VAC, I would guess that complicates things. Now LesterPester has to convert (one way or another) from line to some voltage that makes a 555 timer or a pic happy, i.e. 5V. I think a typical plug-in-the-wall night light has a photocell in series with a relatively high resistance light bulb (5W from line). If that is what LesterPester is doing, then a lot of things will have to change, i.e. relay or triac for light bulb power, etc...

So, LesterPester, what power source is powering your 5W lightbulb?

 

[VEBill]

I thought that 'night lights' market had moved well beyond the type that has 5w or 7w (incandescent?) light bulbs.

In the dollar stores (selling for a cdn dollar, US$0.80) one can see night lights with white or various colour LEDs, or those with the green luminescent light emitting panels that consume almost zero power (0.07 watts). Some even have photocells that turn off (why?) the green luminescent panel that wasn't consuming any significant amount of electric power anyway.

Is the 5w (incandescent?) light bulb a firm design requirement? It sounds so last-century...

Perhaps using a white LED would make the entire circuit low voltage and thus simplify the entire circuit.

 

[LesterPester]

All of you guys that replied to my post. I had to take my wife into emergancy surgery. So yes it is a 120 vac source and yes they are intending to use a 5watt inconddesant light bulb with a photo sensor. And yes I know, I have checked out all of the available ones on the market right now. For myself I would purchase the GE motion detector one. But I think this person is just looking for a marketing ploy in a already filled market. Those lights are so cheep it is unbelievable. All he really wants is for the light to just decay to full off after the customer turns the light off in about 3-5 minutes. I also can't believe that the 555 timer is still being used today. We were using that one in the very early eighty's. Oh well, when you have a good product it should stick around.

Sincerely yours,
Les

 

[Myndex]

I only mention the 555 because it is literally pennnies in even modest qtys.

I think PICs are slightly more expensive, but will lower the part count - though PICs need a tighter supply, and 555s don't.

If you want it to decay, then you'll need some kind of SCR circuit.

The other option is a relay with a bimetalic strip and a heating element, though I'll bet that'll be a custom job for a 3 minute time period.


A

 

[VEBill]

There already exist alarm clocks & clock radios with the 'artificial sunrise' feature where a light bulb (perhaps ~25w) is turned on slowly so as to wake up the owner slowly and comfortably. (If it would only dispense freshly brewed coffee with cream and sugar then I'd get one.)

I'm thinking that there likely already exists wall-mounted light dimmers that provides the slow turn-off feature (for the baby's room). The light dimmer section in Home Depot now occupies about 25 feet of aisle and those endless gadgets offer features that I can't even have imagined.

Those gadgets are often ASIC driven.

For a slow 3-5 minute off cycle, it should be possible to combine the usual SCR/triac light dimmer with some sort of an R-C network on the control side. If you want it to turn on quickly, then you'll need to do something with a diode in that direction to bypass the R.

For 'human factors' reasons, you'll need to think about how to confirm to the operator that the slow-off function is in actually in progress. This reassurance might require another red LED.