What Lurks In The Dark?

There's an old saying, "I'm not afraid of the dark. I'm afraid of what might be in the dark!"

This project is completely harmless, and has no pop-ups, pop-outs, loud sounds, flashes of light, or anything else that actively scares you.

Instead, this is a passive scare.

What if you were in a spooky dark place, finding your way through by the light of a dim flashlight. And when you turned to look into a corner, the flashlight went out? The flashlight works fine - shine it anywhere else. But if you try to shine it in that corner, it always goes out.

What is it that lurks in the dark?

Overall Design

The overall design consists of two parts: one or more doctored flashlights, and a "dark projector".

The flashlights are carried by the victims in the haunt. They appear quite ordinary. They work just fine - most of the time. But they are doctored to turn off whenever they are pointed towards a source of coded infrared (IR) pulses.

The "dark projector" is a small and simple gadget that can be placed anywhere in the haunt. It emits a coded IR beam that turns off any gimicked flashlights pointed toward it.

Schematic

NOTE: I haven't built one of these yet! The theory is sound, but has not yet been tested!

Here is the dark flashlight:
[schematic]
It is based on a commercial IR detection module, like that used in televisions to receive remote control signals.

These modules are simple to use. You feed it power. It outputs a signal when it sees IR light modulated with a certain carrier frequency. The carrier frequency varies, depending on the exact module. They are usually around 40 kHz - 50 kHz.

The power darlington transistor is overkill, even for a big bright flashlight bulb. I'm sure that you can find something smaller and cheaper that will work.

This is the dark projector:
Intended duty-cycle of 50%, but probably will be off a little.
It is a simple 555 timer circuit, tuned to pulse at the same frequency as the carrier of the IR receiver module.

The output is on for t1 seconds, then off for t2 seconds.

t1 = .693 x (R1+R2) x C
t2 = .693 x R2 x C
(R1 and R2 are in Ohms; C is in Farads)

Please fill in the following values and then press "CALCULATE".


R1 resistance		Ohms (use all digits, no K or M)
R2 resistance		Ohms (use all digits, no K or M)
C1 capacitance		uFd

Requires JavaScript 1.1 or newer.

Parts Selection

Flashlight

For the flashlight, select something that is cheap and rugged.

When the light goes out, the victim is likely to knock it against something to try and get it working again.

IR receiver module

For the IR receiver module, find something that is cheap, and above all small and inconspicuous! You don't want the flashlight to appear in any way special.

I found several different kinds at Electronic Goldmine that would probably work. Older models with big clunky metal cases are also easy to find, but less desirable for this project. All of these units are made with a variety of carrier frequencies and slightly different model numbers to so indicate.

manufacturer part number frequency size Electronic Goldmine
part number price comments

Temic TFM 5360 36 kHz 12.5mm tall x 10mm W x 5.8mm thick #G14384 sale: 5 for $.99 large

Vishay TSOP2230 30 kHz 6.95mm tall x 6mm W x 5.6mm thick very small

Vishay TSOP2233 33 kHz 6.95mm tall x 6mm W x 5.6mm thick #G14017 2 for $1.00 very small

Vishay TSOP2236 36 kHz 6.95mm tall x 6mm W x 5.6mm thick very small

Vishay TSOP2237 36.7 kHz 6.95mm tall x 6mm W x 5.6mm thick very small

Vishay TSOP2238 38 kHz 6.95mm tall x 6mm W x 5.6mm thick very small

Vishay TSOP2240 40 kHz 6.95mm tall x 6mm W x 5.6mm thick very small

Vishay TSOP2256 56 kHz 6.95mm tall x 6mm W x 5.6mm thick very small

Temic TFM 5360 is on the left. Vishay TSOP2233 is in the center. Jefferson is on the right.

manufacturer	part number	frequency	size	Electronic Goldmine part number	price	comments
Temic	TFM 5360	36 kHz	12.5mm tall x 10mm W x 5.8mm thick	#G14384	sale: 5 for $.99	large
Vishay	TSOP2230	30 kHz	6.95mm tall x 6mm W x 5.6mm thick			very small
Vishay	TSOP2233	33 kHz	6.95mm tall x 6mm W x 5.6mm thick	#G14017	2 for $1.00	very small
Vishay	TSOP2236	36 kHz	6.95mm tall x 6mm W x 5.6mm thick			very small
Vishay	TSOP2237	36.7 kHz	6.95mm tall x 6mm W x 5.6mm thick			very small
Vishay	TSOP2238	38 kHz	6.95mm tall x 6mm W x 5.6mm thick			very small
Vishay	TSOP2240	40 kHz	6.95mm tall x 6mm W x 5.6mm thick			very small
Vishay	TSOP2256	56 kHz	6.95mm tall x 6mm W x 5.6mm thick			very small

Details

The circuitry in the flashlight is relatively inexpensive, but you still don't want to lose them. Make sure that there is somebody at the end of the haunt to take back the loaned flashlights.

The scare loses its effectiveness if anybody succeeds in shining a light into the dark place.

The room for the scare should have dark walls, so that light pointed elsewhere isn't reflected into the dark corner.
It might help to keep the groups small, so that lots of little reflection don't add up.

Some visitors may have their own flashlights, especially if they are Trick-Or-Treaters on Halloween.
- Perhaps you put a Mini Slave Strobe in the dark corner, so if they do manage to shine a light into the corner, they get blown away with a bright flash.