Mars Analog Clock
Mars Analog Clock
A clock that runs on Martian time.
This technology is also a general purpose clock speed hack that allows running these cheap analog clocks at different speeds
and with higher accuracy.
One Mars second = 1.0274912510416665 Earth seconds.
This clock uses a precision 1 second timebase,
a common DIY clockwork mechanism, and an Arduino program that slows down the clock motor
so that the clock runs on Martian time.
The Mars clock is as accurate as the timebase; using a DS3231 that's about 3 minutes per year.
For better long term accuracy a timebase such as GPS PPS or AC mains frequency could be used.
Parts list:
- Cheap clock from eBay
- Arduino Pro Mini 3.3V/8MHz
- DS3231 RTC module
- 2 red LEDs
- 5V Power Adapter
- 3D printed parts
- #4 heat set inserts and screws
- Micro USB connector breakout
Design Documents
| Schematic Diagram | mars_clock_schematic.pdf |
| 3D Print Files | mars_clock_mechanical.zip |
| Source Code | View Download |
Modifying the Clockwork
The clockwork contains a motor that spins at 8 revolutions per second.
The clockwork case opens up by carefully prying the clips loose. And then the gears spill out. But it's pretty easy to figure out how to put them back when it's time to reassemble.
The circuit board traces to the motor coil are cut with a hobby knife. The original clockwork circuitry, now disconnected, is left in place. And of course it won't need the 1.5V battery any more.
New wires are soldered to the motor coil and routed out of the clockwork enclosure.
The clock motor is very low power so it can be driven directly from Arduino I/O pins. However the clock motor is designed for 1.5V but the Arduino is 3.3V. So a couple of red LEDs are used to drop the voltage from 3.3V to around 1.5V, or close enough that the motor is fine with it. The LEDs also provide a convenient indication of motor activity.
Wiring diagram:
Adding the Speed Hack
The speed hack electronics are mounted on the back of the clock.
This bracket is added to the clock to provide a place to attach the speed hack electronics.
This box contains the electronics.
Optional desktop stand.
Operation
| Red Motor LEDs | Flash at clock stepper motor rate. |
| Onboard LED | Flashes at 1/2 Hz rate to indicate precision timebase is working. |
A mechanical slip clutch allows the hours & minutes to be set at any time, while the clock is running or stopped, using the knob on the back of the clockwork.
Note that the Mars clock will lose time during a power failure. The DS3231 real time clock functions are not used for this clock, only the precision 1 second signal. The DS3231 backup battery is also not used, so it doesn't need to be installed. I power my clock with a mini 5V UPS so it never stops.
Build Pictures
Disassembled front glass and clock face
This cheap clock from eBay was not made to be disassembled easily.
Inside before final assembly
Back view
Arduino + DS3231 Hack Wiring
The yellow wires connect to the clock motor
Clock Hack Close-up
