It knows the time exactly from the ether, but it tells us only roughly. To not forget the time, it has a small battery.
The clock has a nice font, so that it is a pleasure to read. With natural letter spacing, untracked, in monospace with serifs. For German time, no decenders are necessary.
The colour is important, too. A bright orange, which the photo camera does not like, but the clock is not for the camera but for our living room. The colour is 595nm, a wonderful orange, but the camera insists that it is yellow.
To adjust the brightness it observes the environment. It turns darker when we watch a film and the living room becomes cosy. If that is not enough, its brightness can be turned up and down with an infrared remote control, or be switched off completely.
- CPU: Atmel AVR Atmega644 (an Atmega164 would have been enough) @ 2MHz
- DCF77 receiver: ELV with individual voltage regulator LD1117V33
- Real-time clock: Maxim DS1307, battery buffered
- IR receiver: TSOP1740
- LEDs: 595nm highflux LEDs, driven with ~30mA
- Voltage: +5V, regulated with efficient Recom R-785.0-1.0
- Matrix: 8 vert, 11 horiz, fully encapsulated in copper foil to minimise DCF77 disturbance
- Dimming: 255 step PWM at ~1MHz; ~4kHz line frequency; ~500Hz display refresh
- Drivers: PWM capable constant current source, linewise common anode, manually built from transistors (next time: use Max7221)
- Casing: aircraft plywood 4mm + white, glossy acrylic ink spray
- Front: CNC cut 4mm acrylic glass into layer of lamp black acrylic ink
- Mounting: iron sheet + 8 neo magnets 20x2mm
- Glue for iron and magnets: 2 component acrylate glue
- Diffusor: thin plastic bag from farmers market
- Programmed in GNU assembler (under Linux)
- IR reception, DCF reception, brightness control, second pulse from RTC, I2C communication, and display refresh are all in an interrupt
- TIMER0 for PWM (phase correct PWM mode)
- TIMER1 for global system time @ ~1MHz, used for measurements in IR and DCF reception
Other Word ClocksThere are some other variants of the word clock below. There are also software-only implementations, but below, only hardware implementations are listed.
- Large (248 LEDs) in Croatian
- Small variant based on PIC
- First prototype of Doug's commercial ones
- In an IKEA frame
- Wooden frame with a colour birthday message
- German with different dialect modes
- German, multicolour
- Polish version
- Another one in an IKEA frame
- With serif font; hand-carved, it seems