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Electronic Hardware
For all brand-new parts, plan on a budget of at least $160.
| Item | Qty | Approx. Price |
|---|---|---|
| Raspberry Pi 3 Model B+ | 1 | $40 |
| Power Supply, 5V 3A Micro USB | 1 | $6 |
| Parallax Feedback 360° High Speed Servo* | 2 | $28 |
| USB Audio Interface | 1 | $8 |
| Small Computer Speakers | 1 | $9 |
| AC USB-A Power Adapter (if needed for speakers) | 1 | $5 |
| MicroSD Card, 16GB or bigger | 1 | $12 |
| Raspberry Pi Case | 1 | $5 |
| Clock Movement Kit (with 2 movements) | 1 | $9 |
| PCB Wires with Individual Pin Header Sockets | 6 | n/a |
| Total | $150 |
Warning: The servo motors are the most specific, non-substitutable part. The code in Clockworth is designed to work with the model called "Feedback 360° High Speed Servo" (#900-00360) made by the brand Parallax. If you buy motors with a different spec sheet, you will need to edit the code in build/face.c to properly control the new motor.
The motors being high-speed is actually detrimental to our design goals. This results in the clock hands being a little clumsy in their movements and directional precision. However, these motors were chosen for the feedback signal they give. As long as we maintain a 1:1 net gear ratio between servo and clock hand, the feedback allows our software to know where the hand is pointing so that it can calibrate itself, and never require manual intervention.
The way to fix the clumsiness of the hands would be to gear it down, which unfortunately would spoil our 1:1 gear ratio and undermine the whole purpose of having a feedback signal. 😢 If anybody out there finds a 360° servo motor with a feedback signal that's manufactured for low-speed high-precision movement, maybe they could improve on my design.
Until then, I think the clumsiness of the hands adds something to the charm and makes it more subtly apparent that it's a cool robot. After all, you can still tell time from it with plenty of precision for an art project.
- Wire-cutters.
- Soldering iron with solder.
- External monitor / keyboard / mouse, for initial setup of Raspberry Pi.
The wire-cutters and soldering iron are necessary because you need to do some cable-splicing on the feeds from the servo motors, to separate them. They are manufactured with the power/ground/control wires attached in a row, which doesn't work for our needs.
Replace the ends of the conjoined wires with six individual pin header sockets.
Next, choose which motor you want to use as the hour hand and minute hand. The wires should attach to the Raspberry Pi header pins as follows:
| Clock Hand | Wire | Color | Physical Pin No. | Name |
|---|---|---|---|---|
| Hour | Power | Red | 4 | 5V Power |
| Hour | Ground | Black | 9 | Ground |
| Hour | Feedback | Yellow | 11 | GPIO 17 |
| Hour | Control Signal | White | 13 | GPIO 27 |
| Minute | Power | Red | 2 | 5V Power |
| Minute | Ground | Black | 14 | Ground |
| Minute | Feedback | Yellow | 16 | GPIO 23 |
| Minute | Control Signal | White | 18 | GPIO 24 |
(For any italicized row above, you can switch the hour and minute wires and it won't affect anything.)