Foot Keyed CW Transmitter

Plan

The goal is to create a cw (morse code) transmitter that is keyed with your foot. The electronics would be strapped to your leg, with the key in your shoe under the insole. The entire system could be operated discretely, enabling transmission without using your hands.

There really isn’t an intended use case. It’s just a cool idea that’s been floating around in my head for awhile.

Key

Foot key inside a shoe

The sensor is a force sensitive resistor. It varies its resistance depending on the force applied. It is placed far forward in the shoe under the insole with a wire running back and out the shoe. A small connector is placed on the wire so the shoe can be separated from the electronics package.

I was unable to notice the key inside of my shoe. It made no difference in how I walked. The key can be activated by pressing down with your toes. Under normal walking the key will be activated on every step. It might be possible to connect a microcontroller and configure it so taping some pattern will turn the radio on, and off. This way it could be shut off before walking.

Prototype Electronics

The key is set up as an adjustable voltage divider. An op amp comparator compares that voltage to the voltage over a potentiometer. When the voltage over the key is higher than the pot the output goes high. This is sent to the reset pin of a 555 timer configured as a 700Hz astable oscillator.

The system was built on a breadboard and I did not set up any radio transmitters. I connected the output of the 555 timer to a mosfet, and then to a speaker or pair of headphones. Using a computer decoding software I was able to send morse code and have it successfully be decoded.

I was able to use it both sitting and standing up. The maximum speed I could trigger the key was somewhere between 5 and 10wpm, which is about the fastest I can send morse code anyway.

Prototype electronics