DIY Honda CR-V Replacement Clock

As the dashboard clock of my car failed recently, I was looking for a replacement.
Instead of buying an original part, I opted for a DIY solution based on a cheap Arduino Pro Mini 328, a mini real-time-clock (RTC) module, and a 8×2 LCD display:

Clock Prototype on Breadboard LCD Panel with Buttons

The Arduino and the RTC module talk via I2C and the LCD uses a 4bit wide parallel interface. The LCD backlight can be switched between two intensities. It is wired to two Arduino pins at the same time, one directly and the other via a 1k resistor. The LCD draw less then 40mA. As shorting two pins can be rather dangerous for the MCU, the software needs to ensure that the inactive pin is set to high-impedance input mode before the other one is set active.

The Internals of the Dashboard Clock The new Arduino based Dashboard Clock

The initial firmware implements setting the time and manual dimming for the night. As the car-connector also offers a 12V wire indicating when the main-lights are turned on, I could add automatic dimming later on.

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