As of today (12th march 2025) it will be the anniversary of Terry Pratchett’s death. For those that don’t know, he is/was a titan of wonderfully British fantasy fiction. Eric was the first grown up book I read. My sister got thrown by the opening paragraph, and handed it to me in disgust.
Other, better people have written many column inches about his talents, world building and or general greatness. I’m here to concentrate on a different aspect of his personality: the man was a massive fucking nerd.
The discworld, for those that don’t already know, is semi medieval world full of magic, small gods, talking animals, zombie lawyers and semi effective policemen. It does however have a working postal system, a semaphore based telegraph and a sort of railway.
He seemed to like both cutting edge technology. He also cared deeply about how technology shaped or shapes a nation’s mindset. (in stark contrast to today’s oligarchs) Going postal, Making money & Moving Pictures all tackle this head on.
The clacks
The thing we are interested in here is the telegraph system known as “the clacks”. They are chains of semaphore towers that allow fast communications across the discworld. They are called clacks because of the noise made by the shutters that cover and uncover the lights used to send messages.
Xclacksoverhead has a neat explanation:
[in the novel] “Going Postal”, the story explains that the inventor of the Clacks – a man named Robert Dearheart, lost his only son in a suspicious workplace accident, and in order to keep the memory of his son alive, he transmitted his son’s name as a special operational signal through the Clacks to forever preserve his memory:
GNU John Dearheart
G: Send the message onto the next Clacks Tower.
N: Do not log the message.
U: At the end of the line, return the message.
The nature of the ‘GNU’ code would keep the name of his son forever transmitting through The Clacks network so long as the network still existed.
“A man is not dead while his name is still spoken.”
After his death a bunch of discworld fans organised a tribute on Reddit. That tribute snowballed into gnuterrypratchett.com. When I worked at a large website company, I sneaked in the “clacks overhead” into the commenting service. I’m not sure it’s still there.
Making it real
I started investigating if it’s practical to use lasers blasting through “free space” (air to you and me) to link virtual “clack towers” together. Whilst it’s definitely possible to do (and it would look amazing) it requires a lots of setup and continuous maintenance to make sure the lasers are aligned. (I used to administer a laser link. go on, ask me why they aren’t very popular)
I spent a lot of time working out how to create low powered laser transducer, capable of working on something battery powered. I could probably make it, but it would require non trivial optics, and analogue electronic fuckery.
So after leaving it for a while, I remembered that lora is a cheap and ubiquitous radio system for microcontroller. With the popularity of meshtastic, it means there are a bunch of cheap microcontrollers there for the taking.
So instead of making a telegraph linked by light, we are going to cheat and use radio waves instead.
The microcontroller I am going to use is the heltech lora v3 it has a lipo controller, lora radio and strong micropython support.
Radios all the way
This design has ditched the lasers and gone all in to Lora. It also has the rudimentary design for a store and forward network, allowing a “base station” to change messages on the fly.
There are bonus points for being able to piggyback sensors on the lamps.
Hardware selection
Whilst it’s possible to design my own solar powered lamp, it’s expensive to produce, error prone and a massive time sink. So today I’m just going to find something on eBay that fits my spec:
- Solar powered
- Large light
- Large capacity
- Lipo battery
- Outdoor “proof”
- Wall mounted
After a load of searching I hadn’t found anything overly compelling. Most lights appear to be a variation of “the wedge”
Which is both expensive and not very pretty. Mind you, none of the cheap lights are very pretty. But I’m not willing to spend £60 a lamp for something that looks nice. Especially as the budget for all of this is not that much. After much searching I found something that is a good compromise
It’s not pretty, but it is the best compromise. It’s also quite easy to disassemble, and has lots of space to hide a microcontroller in.
Here is the microcontroller shove in the back. The hidden advantage of this microcontroller is that it has a built in mosfet switch that can handle 250 mA. Perfect for the light, and means I don’t need to fuck with transistors. (There seems to be a rule that I am not destined to master 7-segment displays, transistors and 555s. I discovered this to my cost when doing A-levels)
The Result and future
Alas, I have not managed to create a network in time for Señor Pratchett’s anniversary. I have a vaguely working prototype, with a slightly buggy store and forward network.
What I do have is a “weather proof” solar lamp that flashes “GNU TERRY PRATCHETT” every minute or so. More pleasing is that I can make it say rude words at a click of a button.
When I have enough motivation, I want to spread these around London, so I have a mesh of constantly talking “clacks”. This was meant to be a quick project, 1 month max. However as you know, everything takes a year. This is no different.
