Help me make a night light from a stop light

July 11, 2006 6:28 AM

How to turn stop light into night light?

A friend of mine asked how he could turn an old stop light into a night light that changes colors every couple of hours. The stop light is decades old and is simply three bulbs, no printed circuits here.

He would like one light to come on at a preset time then switch to a different bulb a couple of hours later, then the third and finally switching off.

The first thing I thought of was three lamp timers, but he's looking for something smaller and a bit more unified. So, Metafriends, how would you make this work? Solutions involving soldering are acceptable.

posted by kc0dxh to technology (15 comments total)

I bought my traffic light timer from trafficlights.com. Comes with instructions, no soldering required, and took about 20 minutes. It hides inside the casing. You can control the timing of all three lights and the sequence too.
posted by DefendBrooklyn at 6:57 AM on July 11, 2006

If only every question could be answered by pointing to its own eponymous website. This one is just too good.
posted by GuyZero at 7:17 AM on July 11, 2006

the trafficlights.com timers only go up to 60 seconds, though.
posted by sergeant sandwich at 7:38 AM on July 11, 2006

this is probably a really dumb way to go about it, but it sounds fun to me so i'd probably do it this way: hack up a clock radio and use the LED outputs to select a time based on the digits. in other words, to get the green light to come on at time 10:51:



take LED outputs a, b, c, d, e, h, i, g, l, j, m, p, n, v, w and dump them all into a 16-bit AND gate*. take the output of the AND gate and use this as the SET bit on a latch circuit.

in parallel do the same thing with the time you want the green light to turn off, and use that output as the clear bit on a the latch.

do the same thing for yellow and red.

use the output of each latch to drive a relay that powers the light bulb.
posted by sergeant sandwich at 8:03 AM on July 11, 2006 [2 favorites]

ack somehow hit post too soon. digital logic probably won't be able to drive a relay, so you might need something transistor-y inbetween.

* i just spent 10 minutes looking through digi-key and can't find any lots-of-bits logic gates, but i didn't look that hard. you might have to cascade them.

if you have no idea what i'm talking about, just ignore this. (:
posted by sergeant sandwich at 8:05 AM on July 11, 2006

You could use a timer for underground sprinklers to power three relays (solid state or otherwise). Fairly cheap, easily programmed for on and off times and duration. And you could set different patterns for different days on either a weekly, monthly or yearly schedule.
posted by Mitheral at 8:49 AM on July 11, 2006

Mitheral's idea of using a irrigation controler is great. I would just replace the 120v bulbs with 12v ones.
posted by mrleec at 9:25 AM on July 11, 2006

sergeant sandwich's idea would probably work, buuuuut... you need to hook up (and invert) the other sections of the clock as well, or you'll end up with the light turning on at 10:50... not that that is a big deal, but for other times, it might be an issue.
posted by shepd at 10:09 AM on July 11, 2006

sergeant sandwich: I think the term you want is "darlington transistor" or "darlington pair".
posted by Mars Saxman at 12:05 PM on July 11, 2006

I've marked Mitheral's idea of using an irrigation controller as best. I see that many, if not all, of them are limited to a 99 minute run time. I suppose I could run back-to-back programs to achieve the desired result, but it's just a mite shy of perfect.

Thanks for the ideas. Any others?
posted by kc0dxh at 12:10 PM on July 11, 2006

I think that what Sergeant Sandwich really needs for his final stage is an SCR.

That's what's used for variable-intensity dining room lights. The pot controls a voltage sent to the SCR, which actually switches the current which is fed to the lights. SCRs are designed to handle high power. "SCRs are made with voltage ratings of 50 volts to 2500 volts, and with current ratings up to 3000 amperes per device." That should be enough for your purposes.
posted by Steven C. Den Beste at 1:21 PM on July 11, 2006

kc0dxh, here's the plan I'd follow: find yourself a junior or senior college EE student and offer them $25 above component costs to design and build a controller for you.
posted by Steven C. Den Beste at 1:27 PM on July 11, 2006

SCRs would work, but the cost and control issues are only worth dealing with if you want to dim the lights. Otherwise, relays are cheap, easy, and you can drive them from low voltages.

And, of course, kits are the other answer. For example, how about a remote controlled traffic light? Or, for parties, a Color organ? Three channels, three lights! Or a 5 channel programmable chase? Of course, that leaves you with two too many channels, but you'll come up with something.
posted by eriko at 4:37 PM on July 11, 2006

As a junior or senior college EE student I say the Do-It-Yourself way to do it is to get a cheap microprocessor such as a PIC for a couple bucks (you would be able to get by with . Use an external crystal oscillator and it will probably be able to keep time well enough for your purposes.

The microprocessor will handle everything, no need for external logic, just the crystal, transistors, and relays (or transistors and big transistors if you rewire with 12V lighting.) And you could program it to do other stuff with the traffic light if you so desired.
posted by TheOnlyCoolTim at 4:49 PM on July 11, 2006

*(you would be able to get by with just about anything.)
posted by TheOnlyCoolTim at 4:53 PM on July 11, 2006