Alarm clock

The aim of this new project is to build a small alarm clock. This is a work in progress so this page is a draft not very well organized.

• Receive DCF-77 radio timing signals to stay on time
• Internal crystal to maintain time if DCF77 signal is lost
• Battery backup if main power is lost
• Alarm
• Optional time offset (to add x minutes to the real time)
• Time is displayed on 4 7-segment LED displays
• Several status LED (DCF77/internal crystal, main/backup power, offset on/off, alarm on/off)

Input pins needed:

• 3: Rotary encoder (rotation + push) - alarm/clock setup
• 1: Switch - alarm on/off
• 1: Switch/jumper - time offset on/off
• 1: Push button - replay alarm later
• 1: DCF77 timing signal

Output pins needed:

• 7: 7-segment LED display
• 4: Activate one of the 4 7-segment LED displays
• 1: LED alarm on/off
• 1: LED power main/backup battery
• 1: LED offset on/off
• 1: LED time based on DCF77 signals/RTC crystal
• 1: alarm (buzzer)
• 1: anticipative alarm (PWM)

Other pins:

• 2: 32kHz RTC crystal
• 1/2: Analog comparator (detection of main power loss)

In stock: ATmega8L, ATmega16L, ATmega32

• Rotary encoder (to set time/alarm) : http://www.sparkfun.com/commerce/product_info.php?products_id=9117
• Darlington Driver 8-Channel ULN2803 DIP (drive 7 seg display) : http://www.sparkfun.com/commerce/product_info.php?products_id=312
• 7-Segment Red LED : http://www.sparkfun.com/commerce/product_info.php?products_id=8546
• Crystal 32kHz (RTC) : http://www.sparkfun.com/commerce/product_info.php?products_id=540 (12 pF load capacitor)
• DC Barrel Power Jack/Connector : http://www.sparkfun.com/commerce/product_info.php?products_id=119

• DCF77 module
• Transistors to alternatively power the 4 7-segment LED displays
• Buzzer
• …

• Think about power supply (main/battery)
• Think about 7-seg LED display (is buffer needed?, multiplexing, transistor)
• ATmega : choice of ATmega, external crystal, reset
• DCF77 receiver: buy one or build one?