0bCLK

0bCLK

11 LED Binary Clock using an ATmega48A, Datasheet

Code is here

FEATURES:

• Binary Time on 11 LED's with PWM brightnesscontrol
• Control over buttons
• Sleepmode with shown reduce of power
• Timebase using Timer and quartz crystal (accuracy can be messured at PB0)
• Flashing using ISP, for example using a USBasp and avrdude or an Arduino

Schematic:

PCB:

• I used a mill for the 2-layer PCB
• All components are mounted on the top and soldered on the bottom
• I used CR2032 battery cells
• For orientation of the ISP:
  • the square pad on the footprint is the VCC pin of the 6-pin ISP

Command for flashing using avrdude in Windows:

avrdude -c [programmer] -p m48A -Uflash:w:Path\To\CLK\Debug\CLK.hex:i

Example using USBasp, path is "C:\Atmel_Studio\7.0\CLK\Debug\CLK.hex":

avrdude -c usbasp -p m48A -Uflash:w:C:\Atmel_Studio\7.0\CLK\Debug\CLK.hex:i

Power saving:

• If CPU is doing nothing (waiting for Timer interrupt)
  • goes to PWR_SAVE (basically completely off exept async Timer and interrupt)
• Disabling individual Timers, Two Wire Interface (TWI), Universal Synchronous Asynchronous Receiver Transmitter (USART0) and Analog Digital Converter (ADC)
• more optimizations: turning off Watchdog timer, brown out, lower CPU CLK, lower voltage, using sleepmodes

Fuse bits:

• SPIEN: LEAVE ON!
  • else it won't be flashable using SPI/ISP anymore
• WDTON: OFF
  • Watchdog timer not needed
• CKDIV8: OFF
  • no system clock division needed
• BODLEVEL: Maybe
  • if left off a brown out might lead to malfunction

Power usage:

• Default 6,5mA -> 35h runtime
• PWR_SAVE 1,2µA -> 191666h ~ 20 years runtime

CLK inaccuracy:

• Reasons:
  • No Capacitors at quartz crystal, quartz temperature (25°C is optimal)
• Messuring:
  • Output of Pulse Per Second (PPS) Signal at PB0 and meassuring using a counter

Timers:

• Timer 0: every ms for PWM
• Timer 2: every second for timebase

Buttons:

• PD0 -> down (PCINT16/RXD)
• PD1 -> up (PCINT17/TXD)
• PD2 -> mode (PCINT18/INT0)

Ports:

• Data Direction Register:
  • DDR=0: Pin is input (button)
  • DDR=1: Pin is output (LED)
• PORT-Register:
  • if DDR=0
    • 1: Pull-up resistor is active, for button
    • 0: Pull-up not active
  • if DDR=1
    • 1: High voltage output
    • 0: Low voltage output