DCF-Tester and Transmitter
For testing of DCF-decoding routines and DCF-clocks I had build a small DCF-code generator based on a small ATTiny85. It had seven pre-programmed "critical" DCF-time/date combinations and could output an inverted or uninverted TTL-Signal.
For testing of DCF-decoding routines and DCF-clocks I had build a small DCF-code generator based on a small ATTiny85. It had seven pre-programmed "critical" DCF-time/date combinations and could output an inverted or uninverted TTL-Signal.
The "critical" DCF-time/date combinations are those, where a DCF-decoding routine can get confused. These are especially the times when the official changes from standard-time to daylight-saving time are applied. Furthermore it are the times when a DCF-receiver loses synchronisation and has to count the time forward by it's internal timebase. This is critical especially at the switchover from 28./29. of february to march, 1. in agap-year or during the switchover to a new year.
The selection of the preprogrammed codes and the inverted/non-inverted modes is made by dip-switches.
Inspired by the Elektor article-series "SDR mit AVR" (3,4,5/2012) from Martin Oßmann I have added to 2 useful features:
- a real 77.5kHz signal is generated which can set and test any DCF-clock you put near the inductor of the LC-filter (aka ferrit-antenna)! Tests have shown that the signal from the inductor can "reprogram" DCF-clocks up to a few meters distance.
- with the help of a simple RS-232 serial adapter (consisting of 2 resistors) you can set the DCF-tester to any time and date you want with a terminal-program. The ATtiny sends the time-/date-code every second also over RS-232
For that purpose I had to switch over to a sllightly larger ATtiny 84. As you can see from the circuit diagram the whole circuit needs only a handful of easily available components. The ATtiny is programmed in BASCOM and the code can be easily modified.
Discussie (1 opmerking(en))
jan van harten 8 jaar geleden
I own a Prangins RC clock but this Swiss DCF pransmitter is no longer on-air. Could I use your equipment to make a simulated Prangis transmitter? I understand that the Prangins coding is 99% the same as the DCF77 coding, but the carriier is 75khz in stead of 77.5
Thanks for your help
Jan
jan van harten 8 jaar geleden
Best regards
Jan
KainkaLabs 8 jaar geleden
https://www.elektormagazine.com/magazine/elektor-201503/27572
There you can also download the firmware and the source-code (in BASCOM)
If you want to feed in the digital signal with TTL-level into your clock via a cable no problem.
If you want to air the signal with a ferrite-rod antenna as done in my circuit that´s a liitle bit more difficult.
I found by chance that with a 20 MHz quarz you can generate the 77,5 kHz of DCF-77 quite exactly by dividing the oscillator-frequency by 258.
That was the "trick" in combination with a clever use of the PWM-function of the ATTiny/ATMega controller to get the correct AM-modulation and the correct frequency.
Now with a 20 MHz quarz and 75 kHz there is no good divider-ratio to get near 75 kHz. For example 267 as a divider gives a frequency of 74,906 kHz.
That could be near enough to the exact frequency of 75,000 kHz but it depends on the bandwidth of the Prangins-receiver.
You just have to try.
You can change the firmware with the free version of BASCOM to the right divider ratio (267 instead of 258).
Otherwise you could try to find a combination of quartz-frequency and divider-ratio to get nearer to exactly 75,000 kHz.
Best regards
Roger