the quadrant is made out of wood, around 1 m heigh, and weights around 5 kg.
it is mounted on a disco ball base.
the bearing is strong enough to hold it and allow the clock to turn around its center.
originally the disco ball base included a motor, but it was too fragile to withhold the forces.
two plastic gears in the gear box broke.
this was the state of the clock when I joined the team.
I decided to fix the turning clock.
the small DC or stepper motor I tried were too weak to turn the clock.
I decided to use a universal motor salvaged from a washing machine.
the pinout of the motor was undocumented, but not hard to figure out.
two wires went to a small module at the end of the rotor shaft.
this is the tachometer to measure the rotation speed.
it is also easy to trace the two wires going to the brushes feeding the power to the rotor coils.
next, measure the resistance of the remaining pin pairs.
one will have 0 Ohms.
this is the fuse to protect against over-heating.
there will be two pairs of 0.6 Ohms, and one of 1.2 Ohms.
these are the two coils for the stator, with a center tap.
wire the motor with 220V AC the following way:
AC L - fuse - rotor - stator (2 coils, not center tap) - AC N
to limit the speed I used a 4000 W capable SCR.
the SCR was not enough to regulate the motor speed.
setting the potentiometer to a fixed point would results in the motor to stop turning after some time, of to speed up to fast.
the user would have to adjust the potentiometer using then knob periodically to have a somewhat constant speed.
to overcome this limitation I developed the clock jockey.
this device will monitor the speed of the motor using the tachometer, and switch the power to the motor using a Solid State Relay (SSR), so to reach and stay at the predefined speed.
the motor tachometer provides an AC signal.
basically it's a generating motor linked to the shaft of the actual motor.
the AC frequency (and voltage) indicates the speed of the motor.
the AC signal is rectified using a full bridge rectifier.
the rectified signal is input to an PC817 optocoupler (with ~ 200 Ohm inline resistor).
the full bridge rectifier protects to optocoupler, which has a reverse breakdown voltage of 6 V, lower than the seen -10 V peaks of the AC signal.
it also allows to get two pulses per AC period, for a more accurate speed measurement.
the optocoupler is directly connected to the clock jockey.
an omron G3MB-202P (5V) is also connected to the clock jockey to switch to power going to the motor.
the SCR is still in line to limit the maximum delivered power.
since the device is firmware protected (against read-out), you will first need to remove this protection using an SWD adapter and running `rake remove_protection`.
you can then flash the bootloader using SWD and application using DFU a documented in the section below.
There are two firmware images: `bootloader` and `application`.
The `bootloader` image allows to flash the `application` over USB using the DFU protocol.
The `bootloader` is started first and immediately jumps to the `application` if it is valid and the DFU mode is not forced (i.e. by pressing the user button on the board or requesting a DFU detach in the `application`).