I was walking through the hardware store with my wife. High up on the wall was a huge, beautiful wooden clock. Like one meter diameter. Price tag was also pretty high. I said "I can make one like this." My brain immediately started adding features and making improvements. When the permission was given to kick-off the project, I was happy!
- Wooden plate
- Mechanism
- Feedback device
- Motor and driver
- Controller
- Clock hands and numbers
- Power supply
If you don't have a relative or friend that has a woodworking shop, best next option is a local furniture producer. Or recycle some other furniture with nice looking patterns.
Clock with 1 meter diameter needs big and heavy clock hands. Standard off-the-shelf driving mechanism is not strong enough, and it also doesn't offer much challenges. Having a 3D printer in my workshop and with lots of initiative to learn mechanical design, I downloaded Autodesk Fusion Personal and started learning. Produced design is not optimal, but works pretty well. For the next iteration (if it ever comes up) one more gear after the motor is needed to increase the torque. Everything is printed from PLA, as it is hard enough so that gears should last quite some time. PETG was an alternative, as it has better dimensional tolerances and better endurance, but for now it was not needed.
Images: ´3D_Design >> images´
Complete 3D project (Step file): ´3D_Design >> project´
Main idea is that clock adjusts itself to the correct time, and also takes care of the Daylight Savings time changes. For this it is required to know exact position of the clock hands. As an engineer developing the rotary encoders, my first thought was which part from our portfolio would fit. AksIM-2 with 29 mm diameter was a perfect fit. With 17-bit resolution this gives more than 2000 counts between two neighboring minute marks on the clock face. A bit too much isn't it :) But this can be used to make a very smooth and precise time-keeping. As encoder has RS422 differential output, a line-driver is required to convert signals to 3.3V LVTTL for the processor.
With very low space available, the only motor that would fit was some thin stepper. AliExpress delivered again. Two variants were ordered, first one with 90 steps didn't have enough torque, so slightly thicker motor with better precision and better build quality was a good candidate. 0.9 Degree Mini 36mm Round Thin Stepper Motor
Having a stepper driver at hand from some other project was beneficial. ST-Spin family has some really great devices. PowerStep01 chip is way too powerful for what is needed here, but pure sine wave driver with 128-microstepping and quiet voltage mode really makes difference in this project.
The programming work starts here. We need something easy to use, powerful, with lots of peripherals and of course Wi-Fi connectivity. ESP32 series is an easy choice.
- Wi-Fi is used to get current time from the NTP server
- MQTT client talks to the Home Assistant
- UART polls data from the encoder
- SPI Sends commands to the motor driver
- ADC reads the temperature sensor of the motor
- RMT peripheral controls the addressable LED strip
- Flash filesystem is used to store system messages for later review
Everything designed in Autodesk Fusion Personal and printed from PLA or PETG.
120 LEDs is a nice number to have one pixel per minute plus one in between. 60 LEDs per meter is a good choice for nice and uniform colors. The Chinese guys delivered again. LED strip is mounted using custom brackets, as can be seen in the folder ´3D_Design >> images´
Such a project can't be battery powered. A standard 24 V, 1 A, wall-plug supply works well. 24 V is for the motor driver.
- Traco power TSR 1-2450 powers the ESP32 board and encoder (1A limit).
- Traco power TSR 3-24150 powers the LED strip (3A limit).
And then the family starts enjoying the new decoration in the house.
