What is the relevance of all this you ask? Well, if I wasn't going to use a computer to teach networks, then I needed some kind of cheap network device that I could use as a teaching tool. Something that would have analogues (pun duly observed) to the real-world vagueries of wireless communications, with line-of-sight constraints, appreciation of dissipating power over distance, directional receivers for excluding interference and improving gain, and the plain old unreliable nature of physical layers generally.
I've been reading too much Pratchett lately, so immediately decided that the best solution would be a simple clacks or semaphore line system.
Pratchett's clacks system uses shutter semaphore, but that is really too tricky to build for $20 a tower (even old Pony needed more in AM$), let alone drive in duplex with a single operator sitting in a $7 chair.
So I have opted for a cable operated single arm semaphore with a range of about 170 degrees, since the single actuator can be easily operated by foot, allowing the operator's hands to be free to write down what they see on the next semaphore tower.
You can see the arm of the semaphore tower in the image, with actuator cable attached.
So let's get started.