Antique Clock Start Stop Automation

The antique clock from my grandmother has a unique sound. It's bells are resonating through the house. Unfortunately, not all it's residents can enjoy the sound of clock bells during the night, so we stopped the clock in the evening and started it again in the morning. Since this was often forgotten, the clock was not always running and in other cases it was necessary to fast-forward to the correct time. Luckily, the design of the clock allowed for a rig that could automate the start and stop procedure.

Of course not all clocks are suitable for this kind of rig. In this case, the pendulum swings quite close to the bottom of the clock casing. Therefore it is possible to create a rig that sits on the bottom but stays out of sight.

The control is performed by an AVR Atmega88. It might be a bit overqualified for the job, but it has the advantage of having a timer that can be clocked from an external crystal, so it is very easy to make it an accurate clock using a simple watch-crystal (32.768kHz). Also, the mega88 works on voltage below 5V, so it can be powered by 4 rechargable batteries (4.8V). Since the stepper only moves about 40 seconds each day I suspect the batteries won't need to be charged that much.

The rig contains a stepper motor to start and stop the pendulum from the clock. This actual stepper is a 5V type, so it will work with the battery power of 4.8V. It also has a 1/64 gear so it's not really fast, but compensates in sturdyness to absorb the pendulum impacts. On each side there is a switch to detect the rest position of the pendulum start/stop arm. Apart from the AVR there is only a ULN2003 to drive the stepper, a watch crystal and a LED, so it's only a 4 parts circuit.

The AVR program is very simple. The watch crystal triggers an interrupt that counts the seconds. When 12*3600 seconds have passed the clock is started. After again 12*3600 seconds the clock stops. A led light blinks each second so you can establish the startstopper is still working. Stopping the pendulum is accomplished by moving the stepper arm in vertical position very very slowly. After the pendulum has come to a full stop, the arm is returned to rest position. Starting the clock simply flips the arm over (AVR Code).

Here is a demo vid from the first prototype: Clock StartStopper Prototype

After fixing the last bugs the clockstopper is airbrushed to become almost invisible and now fully functional: Clock StartStopper Final

In this case, the rig is set to a startstop timing of 60 seconds to demonstrate.