Boss Alarm

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Making the Squirrel Transmitter

The transmitter is a simple astable 555 timer circuit. The 555 timer is a popular and versatile (and some might say dated) IC found in many hobbyist projects.

The parts you need for this component of the project are:

  • 220Ω, 2.2kΩ, and 10kΩ Resistors (1 each)
  • 10kΩ potentiometer
  • 1nF and 10nF ceramic capacitors
  • Infrared LED
  • 555 timer (x1)
  • 9V Battery Connector and 9V Battery
  • Snapable Protoboard
  • Heatshrink Tubing

Here's the circuit diagram:

Squirrel Transmitter Circuit

The infrared receivers we are using have built-in filtering that makes them very reliable for digital communication. However, in order for the receivers to see our infrared beam we need to modulate it (turn it off and on) at 38kHz.

When operated in astable mode, the 555 timer will oscillate between high and low voltage at a frequency determined by external resistors and capacitors. If you want to learn more about how to work with a 555 timer, there are several websites dedicated to the chip.

Let me remind you of the pinout for the infrared receiver:

TSOP Pinout

Ask me why I know this by heart...

Solder together the circuit in the diagram, try to keep it a bit compact so it fits in the model nicely! The squirrel can accommodate a 9V battery and a circuit board about 1.25 X 1 and 0.5 inches tall.

Squirrel Circuit board

The Squirrel's circuit board

Don't solder the infrared LED directly on the board. Instead, solder some longer-than-you-think-you-need wires onto the LED's terminals making sure to note which one is the anode (+) and which is the cathode (-).

Soldering leads on the LEDs

To avoid short circuits, you should put some shrink wrap tubing on the soldered connections. You can use a heat gun or a blow dryer to shrink the tubing. I used a lighter but be careful not to melt the LED or yourself.

Shrink wrap on the LEDs

If you are using the printed models, I recommend painting them so they blend into your desk's knick-knacks better.

You can install the infrared LED in the squirrel's acorn. You may need to drill out the hole a bit to make the LED fit. Feed the wires through the model until they come out the bottom and then use a little hot glue to keep the LED in place. Tuck the wires away, and then no one will notice the squirrel is actually a nark!

Squirrel Circuit board installed

The squirrel's circuit board installed

Squirrel Overview

The finished squirrel transmitter