The Solstice Clock – Part 3

schematic of solstice clock prototype
Solstice Clock Schematic

Solstice Clock Circuit Design

In part 1 and part 2 of this series, I started to describe my concept of a Solstice Clock and some of the design parameters. This post is just a brief note to present the circuit schematic for the clock motor driver and the corresponding circuit board layout.

Minor Changes

I have made a minor change to the circuit as described in the previous article. The circuit now includes an 8-way DIP switch rather than a 4-way one. The reason for this is to provide a means by which the length of the pulses driving the clock motor may be controlled. Too short a pulse and the clock may not tick or – even worse – tick intermittently. Too long a pulse and excessive power is consumed. Whilst I do not see the solenoid or microcontroller getting burned out, a reduction in battery life would occur.

In a production environment where only one type of clock mechanism is being used, it is possible to find a pulse length that works with all members of a batch of mechanisms and set the pulse length in the firmware. For prototypes however, especially when different mechanisms may be used, the ability to change the pulse length without re-programming would appear to be most appropriate.

Board Layout

Solstice Clock Board Layout

The image of the board layout presented here is – theoretically – 1:1 scale. It is on my computer but I have no idea how other web browsers may mangle it. For those in doubt, it has about the same footprint as a box of regular safety matches. Before you say "whoopee, isn't it small?" I would advise that this is just the controller board. Somewhere in the back of the clock we need to fit in a pair of AA cells to power the thing. These may be either in two single holders (might make it easier to fit in) or together in a side-by-side holder.