I have been playing around with interfacing relays and stuff with a serial port. The kids and I did a fun project of building a squirrel trap. I thought I would cool to combine them together.

A Soekris single board computer is the brains. This is a little low power 486 computer. A laser pointer is used to detect when something is inside the trap. A small electric motor is used to pull the pins that hold open the doors.

A circuit is connected to the serial port that detects the beam. When the beam is broken the computer detects it. A relay is connected to the serial port. When the computer turns on the relay, a small electric motor runs and pulls the pins that hold the doors open. The doors shut and close the trap. The computer then takes a picture with a webcam and sends me a page.

Ever wanted to make your own laser beam security system. You know the kind they have in the movies, with dozens of lasers and the thief has to limbo through them.

Well, I just made a simple laser beam break detector. My computer can now tell when the beam is broken. The parts I used are:

1. 5.6k resistor
2. photo diode, Digikey part #PDB-V107-ND
3. serial port from my PC

You set the RTS pin of the serial port high. You then use the CTS pin to track the state of the photodiode. When the beam hits the diode, current from RTS will flow into CTS and the CTS pin will show high. When the beam is broken, the diode stops the current flow and the CTS pin goes low. Below is the circuit:

My latest project has been transmitting audio/sound over a cheap laser pointer. I found the original plans for this here.

The parts I used are:
1. Laser pointer level from Target
2. Cadmium-Sulfide Photocells (Radio Shack part 276-1657)
3. Audio output transformer (Radio Shack part 273-1380)
4. battery holder for 1 AA battery
5. battery holder for 3 AA batteries
6. Audio source ( I used the line out of my laptop)
7. Headphones
8. small piece of a dowel rod.

I picked the Target laser pointer level because it was the easiest to hack. First take the dowel rod and put a small nail in one end. Attach a wire to the nail. Put the dowel rod into the tube that holds the battery, then use a rubber band to hold it in place. Second attach a wire to the base of the laser pointer.