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A friend is starting a small business that rents a resource for 30 minute time slots.She looked for a timer that could alarm every 30 minutes (on the hour and half hour) with a pleasant gong sound, but couldn’t find anything.

I offered to create a simple Arduino-based alarm clock.
This design uses a Pro Micro microcontroller, DFPlayer Mini MP3 player, and a DS3231 real-time clock (RTC.)
I used Fusion 360 to design the case, based on the Fusion 360 Tutorial – Easy Snap Fit Cases!

Arduino Pro Micro, 5 volt, 16 MHz
DFPlayer Mini MP3 player
MicroSD card
1602 16x2 LCD with I2C Interface
small speaker
2 small SPST pushbuttons
5 volt DC power supply
Barrel jack for power input
various screws/standoff/nuts, etc.
perf board
female and male 2.54mm headers
3D-printed case”

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