Switch on a light box for 45 seconds

If you'd like a store bought solution, stop by a camera store and look at their darkroom timers. Gra-Lab is a good source for this in the States.

If you'd like something a little less expensive, get a 12VDC wall wart and the Velleman MK-111 Interval Timer kit. It uses a 555 and a relay to give you exactly what you need. It includes circuit board and all components except the wall wart. The relay will switch up to 3 amps at

Questions of this type usually receive a better response on sci.electronics.basics.

Good luck Chris

I am assuming you want it to work like this: the user pushes a button, the light box comes on, stays lit for 45 seconds, then turns off until the user pushes the button again. I am also assuming that the light box operates on regular wall-socket voltage from a regular wall socket, and that you have someplace to put the control circuit.

If the above is true, then what you probably want is a "delay on break" or "delay on release" relay. This is a relay (an electrically operated switch) with an internal timer. There is a knob on top of the relay that sets the time it stays on. These relays are usually designed to plug into a standard socket, so you'd need to get a socket as well. You also want to make sure you can get one that can be triggered by an external (pushbutton) switch. You'll probably want to use a fairly beefy pushbutton (like the ones used on arcade games) so it will last.

At the local electronics distributor, I can get a suitable relay and socket for about US$65. Add another US$20 or so for a pushbutton, wire, etc. The relay and socket will fit in a 3" (75 mm) cube. You'll have a plug, a cord, the relay socket, the wiring to the light box, and the wiring to the pushbutton.

If you're not familiar with wiring up things that plug into the wall, get someone that is to help you with it. It's not that hard to do, but the consequences of getting it wrong can be severe.

Matt Roberds

Over here you can get light switches that do exactly this (intended for use on staircases) maybe possible?

The other thought I have is that a photographic enlarger timer does what you need.

Regards, Dan.

I'd go to a hardware store and ask for one of those timers which runs a bathroom extractor fan for a fixed period after the light is turned off.

An off-the-shelf solution will almost certainly be cheaper than a homebuilt one once you factor in the cost of putting it in a box, providing a power supply for the electronics, etc.

Alan

It's not clear which of these you want:

a) a ready-made, shop-bought circuit just requiring careful connection (by someone qualified, possibly yourself, as presumably the box is mains-powered)

b) a circuit you can build

If the former, then you've had several recommendations.

If the latter, then you could base it on these circuits:

with suitable Rt and Ct. For example, combinations such as

You haven't specified power supplies, or switch type, so adapt as necessary.

They're probably only making 10% of the quantity per year that they used to make. Maybe less with all the used stuff floating around.

Best regards, Spehro Pefhany

This is a straight forward application of a timer relay. Press the momentary switch, the relay applies power to the load for 45 seconds and then removes power- regardless of the state of momentary switch after the initial press. If you want the momentary switch to override the time-out, then jumper terminal 8 to 2. This will cause the power to be removed at the later of switch release or the 45 second time-out. There are so-called OFF-(MOM)-ON type switches where the push action can make it either momentary or permanently on which may be useful for that mode. If this is for a viewer activated display, then you would not want this mode of operation- do not jumper 8-2. Mate the line feed solid copper to stranded 14ga type to make the 0.25" crimp terminal connections- do this with wire nuts. All of this can mount in a standard wall mount switch box. Avoid any web based so-called electronic projects or hobby type crap.

View in a fixed-width font such as Courier.

NEMA ENCLOSURE +------------------------------------------------------+ | | NTRL |(WHITE) >--(WHITE)------------------X-------------------------------|--->

| | to lamp | | +---|--->

| | --------------- | |(BLACK) | | / /| | | LINE | +----HRDS4XX----+ | | | >--(BLACK)------X-----------|----------------+ | | | | | | | | | | | | | | | +--------|---------+ | | | | | | | | | | _|_ _|_ | | | | | | | | | 8 1 | | | | | +-----------+ | | | | | | | | | | | +-------|3 2|-------X | | | | | | | | | | | | |o | | | | | | | | --| | | | | | | | | |o | | | |4 | | | | | | | | | screw | | | | | +--+ | | O | | | | | | | 5 | | | | +-----------+ | KNOB __ | | | | momentary | | | | | sw +---------------+/ | | | | ~ 3 x 2 x 1.5 inch | +------------------------------------------------------+

X= wire nut junction

See:

I'll say- all that GraLab stuff is over-priced glitz, even a foot switch is $60- any kind of electronic timer $200.

I don't like that suggestion and I'll tell you why: you go buy that retail trash and what you end up with is an inferior imported knock-off product cashing in on the reputation of the American made product at the high price- plus the timing interval on those is in the 5-10 minute range.

kind

go

button,

until

box

and

break"

operated

You

last.

wire,

have

the

but

If yoe are interested in an off the shelf solution look at:

In message , snipped-for-privacy@yahoo.com writes

Rswww.com part number 490-194 for example.

Cheers