A Big Clock
Since EMF Camp, a few of us have gotten a little crazy at the hackspace and we now have two competing telephone providers. Nottinghack Telecom plc (mine, and therefore the official telephone provider), and MoopTel (Steve's, and therefore the unofficial telephone provider). It's been good fun, and while we like to play out a rivalry between the two, we're just being silly and having fun.
Even though I'm holding EMF responsible, it's not actually entirely their fault. I've always quite liked telephone things, and that era of electronics. A few months back I posed about my GPO alarm lamp, so it makes sense that I might be looking out for other silly General Post Office telephone things. Clocks are pretty cool, and there was quite a cool 18 inch one on eBay, which I decided to buy. I thought it would go nicely in my bedroom, since that's where the alarm lamp is currently, but it turns out that a loud clunk every 30 seconds is quite annoying.
30 seconds I hear you ask? Yes! This is a "slave" clock, and this particular model likes to be pulsed every 30 seconds. "Back in the day" there might have been several clocks (who knows how many!), all driven from one master clock. It's nice when all your clocks are ticking at the same time.
I only have this clock, so I decided to build a small circuit to drive it. I have an excessive number of ESP01 / ESP8266 modules, so I decided to use one of those. I ignored the WiFi. This first version was an unholy combination of surface mount and through hole components, on perf board. I was quite surprised by how accurately the ESP8266 is able to keep time. Anyway, it's pretty much just a BSS138 mosfet and a 3.3v regulator.
Anyway, that was a bit gross, and I wanted some buttons so I could advance time, so I made a nicer version using an ATTiny 1616.
It currently runs around 20 seconds slow per day, despite trying my best to get interrupt timing as close to reality as I could. Really the 1616 probably wasn't a good choice for this. As far as I know, it's using an internal RC oscillator, which will likely drift with temperature. This is a very good excuse to get one of those cool 10 MHz GPS reference clocks though, so maybe I'll bodge one of those into this at some point.
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Comments and feedback are welcome by email (aaron@nospam-aaronsplace.co.uk).