K-9, the robotic companion to the Fourth Doctor, was my first project and I learned a lot from making him. Since the BBC had long ago released plans for K-9, I thought that this would be an easy project to do. I was SO wrong. It was much harder to do than I imagined. I found the plans that the BBC released. Sadly several dimensions were missing.

10 Things I would do differently next time
- Use a better amplifier.
- Add a method of sensing people to start interaction.
- Use servos to control the radar (ears), gun (nose) and wagging tail.
- Build the whole body from lighter materials.
- Change the head (in the plans issued by the BBC, the dimensions for the head are incorrect).
- Use an ISD2560 IC for the speech or similar IC.
- Remote control drive.
- Make the electronics accessible via a panel on the side of the body.
- Use PCBs instead of using stripboard for the electronic circuits.
- Make the electronics more modular.
I did not initially make a list of features that make it recognizable as a character. But if I had it would be like this.
- Speech
- Glowing eyes
- Retractable sensor
- Retractable gun in nose
- Printed paper strip out of mouth
- Oscillating dish ears
- Tilting head
- Television screen on side of dog
- Wagging tail
- Computer on back
- Side panel removable
- Remote control drive