Have you ever looked at a clock and thought it could do with a few more hands? One for weeks, months and years? Maybe a few for wind speed and temperature? Maybe not, it would make it a bit hard to read.
Ok how about one hand, to tell you where we are in the current calendar year? You’re on board? Great! Let’s build it.
To begin we need a motor, one which can be positioned. There are really two options here, a stepper motor and a servo motor. Both are designed for position control over high speed, which is perfect. The servo motor lacks the accuracy we need so let’s go with the stepper.
Problem 1: An arduino can command a stepper motor to step a set number of steps, but not to go to a particular position. This can be achieved by adding some feedback into the system. A magnet on the motor shaft and a magnetic flux sensor on the motor casing just below it produce a signal that can be used to ‘home’ the motor. From home we can move a certain distance to a particular position. Great, now we can map steps to days in the year and we’re set!
Problem 2: The clock will move once a day, to the home position and then to the desired day position. This means that for most of the time it’s doing nothing and could even be switched off (The stepper motor will hold its position even when turned off). So let’s do that, arduinos are pretty power hungry and will chew through batteries pretty quickly, this prompted someone somewhere to make a very clever little device which switches the arduino on, waits for a signal, then off, and then a pause for some set time (2s - 2hrs). This is perfect, we can have our system update itself but consume a very small amount of power. The device is called the TPL5110 Low Power Timer, it deserves a better name.
So we have a prototype. A few months on the wall as a long form test and we’re ready to make it look good. My Auntie is a brilliant artist. Let's see if we can convince her to paint a good looking clock face.
Voilà! It looks amazing.
The small paintings all around the face correspond to events and occasions throughout the year, my favourite is the snowman. There are also birds for each season and seasonal trees in the centre. To attempt to match the theme and feel of the artwork I 3D printed a twig with leaves to act as the hand.
Ok almost done, just a final look round the back. Here we find all the electronics required to keep time, drive the stepper motor, regulate power and of course run the show! Phew, quite a lot of stuff for such a seemingly simple project, luckily there are all very low cost components. One advantage to this design is they are all easily replaceable if they go wrong (they are socketed to the PCB).
Thanks to my Auntie Sandra for collaborating on this project with me. Here's a video of it operating. There is a reset button at the back which homes the hand and sets it to the current day.
Overall I’m pleased with how it came out, but I’m happier with the look of it more than the electronics. A version 2 (if it happens) would have fewer components and try to simplify the design, the stepper motor can be a lot less “beefy” I think and this could help cut out a few steps and problems.