[ntp:questions] Issues with decoding Raw DCF77

Hans Jørgen Jakobsen hjj at wheel.dk
Wed Mar 21 16:46:35 UTC 2018


On Tue, 20 Mar 2018 21:16:11 +0100, Andreas Mattheiss wrote:
> Hello,
>
> I'm monkeying around with raw DCF again ...
>
> I have slightly modified a DCF77 alarm clock so that it constantly
> receives the DCF77 signal and tapped into the 100/200ms pulses. Receiption
> must be good, since when I pipe this into an Arduino board I get good
> results from the decode. For the PC, I first inverted the 100/200ms pulses
> with a transistor, then feed the inverted signal into a MAX232 level
> converter - inverting is necessary since the MAX232 inverts the CMOS level
> signal itself. The MAX232 has a LED at the output that now duly shows
> 100 and 200ms flashes - i.e. it is out most of the time. Hook up to ttyS2.
>
> So far, so good. Alas I only get crap:
>
> 20 Mar 20:59:53 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 20:59:53 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 20:59:54 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 20:59:54 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 20:59:54 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 20:59:54 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 21:00:00 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P124812124124811248----"
> 20 Mar 21:00:03 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "#--############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 21:00:03 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 21:00:03 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
> 20 Mar 21:00:03 ntpd[15775]: parse: convert_rawdcf: start bit / parity check FAILED for "###############RADMLS1248124P124812P1248121241248112481248P??"
>

Despite LED shows plausible pulses there might be noise spikes
triggering false pulses.
I have had a DCF77 receiver where I had to filter out fake pulses.
A scope will be able to show if signal quality is ok.

Are you shure that you have polarity right?
I think wrong polarity would make it trigger multiple times pr second.

/hjj



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