Attempting a timer or motion sensing switch between two LEDs -- crosswalk sign

Thread Starter


Joined May 4, 2009
Hey, all. I'm new here, but this seems like a knowledgeable, cordial forum to ask questions. I confess I'm not as educated as I'd like to be when it comes to crafting original circuits -- I usually either use very simple designs or I appropriate existing circuits from other devices and kludge it together to accomplish my goals. I'm seeking advice here because have a potentially ambitious project in mind, and I'm hoping to get some input and hopefully a nudge in the right direction.

I recently came into possession of a handful of excellent used crosswalk signs, the kind with the White walking figure and the Red hand. Here is a link to the exact items.

I've been tampering with them to see what I can accomplish, and what sort of power requirements I'm working with. What I have discovered so far:

They are actually VERY simple inside. The signs have three input leads -- one positive for red, one positive for white, and one shared ground. Each input lead connects to a separate transformer inside the casing, and each transformer is connected to a separate LED panel. So when 120v current is applied to the Red+ input lead, the "red" transformer causes the red side to light up. And when 120v current is applied to the White+ input lead, the other "white" transformer causes the white side to light up. Each transformer supplies ~9v to the LED panel itself via a small pair of wires and a tiny molex. All very modular.

As a test I have already wired one of the Signs up with a high-current on/off/on switch -- I have a 120v wall-plug cable going into one of the two transformers. The switch itself only switches the 9v output between the red side's panel and the white side panel, so I can display it on a wall and use the on/off/on toggle to switch colors. :p

This is interesting and functional, but not exactly compelling. I had some more interactive ideas...but THIS is where I can use some assistance: actually implementing them.

The most simple option I considered was using a 555 timer circuit to switch the 9v between the two panels on an adjustable delay, maybe using a variable resistor or somesuch. I've found some decent schematics online, though I don't completely comprehend what I'd be doing with them. :confused:

Ideally, what I'd REALLY like to do is use a setup that will detect movement and switch the white to red or vice versa, then switch it back. Sort of like this alarm circuit here.

The only problem is that while I can find lots of circuits to simply turn things ON when they detect motion, and there are plenty of existing devices to steal the motion sensing circuit from, I don't know enough about electronic engineering to build a circuit that will keep LED A on and LED B off until a motion sensor is tripped (either PIR or ultrasonic) at which point it will toggle LED A off and LED B on. Perhaps even make it so that LED B flashes when it is engaged, if I want to get really fancy with it.

I've looked at tons of 555 tutorials, which mostly go over my head, and lots of schematics for Traffic Lights and Train sets. I searched through the forums here, but didn't see anything that quite matched my circumstances, and I fear I'm not clever enough to make this happen by myself. From all the disparate research I've done, I'm sure it CAN be done, I just don't know HOW. Kind of like knowing what goes into a cake, but not knowing how to bake it.:(

So if anyone knows of an existing circuit for what I want to do, or a close match I can examine and learn from, or even an appropriate logic/IC tutorial for beginners I can check out, I would definitely appreciate it. Nothing is as frustrating as knowing what you want to do, and knowing it can be done, but not having the smarts to figure out how.

Thanks for reading and humoring me in this obviously amateurish endeavor. :rolleyes:
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If you're looking to toggle your signs upon each fresh activation signal, then what you need is a divide-by-2 counter, AKA T-type flip-flop. The signs are controlled by the complementary outputs.

If you want to toggle the signs back after a delay, then something like an SR latch with an event-triggered monostable controlling the Reset signal would work. Again, the signs are controlled by the complementary outputs. A 555 would be ideal for the monostable.

More than this would require a tighter spec - you have to decide exactly what you want. It's good to be a bit open-ended at the concept stage of a design, but before anything can be prototyped a design needs a functional requirement specification.