Cheapest timer for a 5w light bulb for 3-5 min
Cheapest timer for a 5w light bulb for 3-5 min
(OP)
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
Sincerely yours,
Leslie H. Howell





RE: Cheapest timer for a 5w light bulb for 3-5 min
2) In your "normal light sensor" circuit, add a 555 timer, set for 3 to 4 minute duty cycle.
Andy
RE: Cheapest timer for a 5w light bulb for 3-5 min
Dan
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RE: Cheapest timer for a 5w light bulb for 3-5 min
RE: Cheapest timer for a 5w light bulb for 3-5 min
So, LesterPester, what power source is powering your 5W lightbulb?
RE: Cheapest timer for a 5w light bulb for 3-5 min
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.
RE: Cheapest timer for a 5w light bulb for 3-5 min
Sincerely yours,
Les
RE: Cheapest timer for a 5w light bulb for 3-5 min
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
RE: Cheapest timer for a 5w light bulb for 3-5 min
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.