#Simple clock

This is just a small project that aims to make a simple clock, using STM32F103C8T6. The clock will be shown on a seven segment display. There will be multiple modes to show on the clock display.

#HW

STM32F103C8T6 is used as the brains. It has RTC that may be powered by CR2032 battery. It's connected to a USB header, allowing to communicate with a computer. The chip is capable of being a device, only, not host. There is a header with 3V3, SWDIO, SWCLK, GND to allow programming the chip using a tool such as STLink. ASM1117-3.3 is used for stepping down from 5V to 3V3. 3V3 should not be connected whilst USB is connected as well. This would short output of the LDO to 3V3. There is no protection!

There are 8 seven segment displays, 4 of them are blue, 4 of them are yellow, the whole display looks like this: Y.Y.BB:BBY.Y. (Y for yellow digit, B for blue digit) There are 4 LEDs and 4 buttons, the LEDs are next to the buttons, making each LED "associated" with a button. That makes it possible to light up an LED next to button, if the button is pressed etc.

The digits of the seven segment display are connected to PNP transistors. When pulling the pin connected to the transistor low, the digit is turned on. The pins used may be connected to timers, and PWM may be utilized to set brightness. Segments get turned on by being low as well.

Mapping of pins to peripherals is documented in pins.

#Features / Roadmap

• [-] Remember date, time
  • [x] Time
  • [-] Date (does not calculate months, years correctly)
• [x] Switch between view modes by button
• [x] Show time, date
• [x] Adjust brightness using PWM
• [x] Auto adjust brightness based on time
• [ ] Stopwatch
• [ ] USB communication
  • [ ] Set time, Get time
  • [ ] Show arbitrary text or number on the display
  • [ ] Start stopwatch

#Images of the clock

#Front, off

#Back

#Front, with seconds

#Front, with clock and date

#What's next

Currently the project does not support setting the clock using the buttons, to set the clock, it's required to use rtc.set_time by flashing a program with this line. Then this line should be removed, that will ensure the clock is remembered even on power down - if battery is connected. For adjustments, a button has to be programmed to add/remove a second or two, to get the clock synchronized with real time.

Unfortunately, I did not solder the USB correctly on my board, so I cannot currently test sending and receiving data using the USB, that is the reason why the current program does not even support USB. In the future, the firmware should support USB communication and a program for a computer should be made, with some kind of CLI for communication with the board.

Another thing that could be done is a bit of a refactoring of the main function. I am quite new to Rust and I don't know how to split the initialization of peripherals to multiple functions naturally. Now the main function is very long, because all initialization is in there.