DCF77 receiver and decoder

For detailed info see my Receiving and decoding the DCF77 time signal with an ATMega/ATTiny AVR blog post.

Scripts

build.sh: build the C code and program the AVR.

build_loop.sh: build and program the AVR if programmer is connected, start terminal if serial converter connected, repeat.

Samples

Check samples.txt for captured and decoded DCF77 packets.

Debug mode

Enable debug mode before building in defines.h for more verbose messages.

NOTE: if debug is enabled then the first bit might be invalid as transmitting the message may take longer time than the first bit and the edge might not be detected properly.

Status line:

Example: l:123 s:1 i:05 v:1

l: length of low signal (in cycles)

s: state
  0: waiting for sync
  1: receiving signal

i: index (nth bit is being received)

v: value decoded
  0: bit value 0
  1: bit value 1
  2: sync period
  3: invalid (too long or too short)
  4: none (i.e. timer overflow)

Messages:

sync ok: sync period found, starting to receive the actual data

restart: unexpected or invalid data received, back to start

completed: successfully received 59 bits of data

incomplete: the data in buffer is incomplete, will not attempt to decode

Decode errors:

e1: start bit is not 0

e2: minute start bit is not 1

p1: first parity bit is invalid (minutes)

p2: second partiy bit is invalid (hours)

p3: third parity bit is invalid (days, day of week, months, years)

e3: minute mark bit is not 0

Structure of a DCF77 packet

0-00010100101001-00010-1-1100100-1-100000-1-010010-001-10001-00000100-0-0
| |------------/ |:|:| | |-----/ | |----/ | |----/ |-/ |---/ |------/ | |
| |              |:|:| | |       | |      | |      |   |     |        | minute mark (always 0)
| |              |:|:| | |       | |      | |      |   |     |        parity for prev. section
| |              |:|:| | |       | |      | |      |   |     years
| |              |:|:| | |       | |      | |      |   months
| |              |:|:| | |       | |      | |      day of week
| |              |:|:| | |       | |      | days
| |              |:|:| | |       | |      parity for hours
| |              |:|:| | |       | hours
| |              |:|:| | |       parity for minutes
| |              |:|:| | minutes
| |              |:|:| minute start bit (always 1)
| |              |:|:leap second announcement
| |              |:|CET
| |              |:CEST
| |              |summer time announcement
| |              call bit
| civil warning bits and weather information
start of minute (always 0)

The values are encoded digit by digit in BCD:
  a b c d e f g h  =>  a*1 + b*2 + c*4 + d*8 + e*10 + f*20 + g*40 + h*80
  0 1 0 0 0 0 1 0  =>  42
  1 1 1 0 1 0 0 1  =>  97

Hours: in 24 hours format

Day of week: 1 is Monday ... 7 is Sunday

Years: within century (two digits)

Try to decode using the JavaScript decoder: tools/decode_js/decode.html