+ This is a lua program intended to be run on an ESP8266 loaded with + nodemcu. It will parse pulses from a + pollin + DCF77 receiver module. It's + output on the serial port (usually available over USB) will be + NMEA GPZDA sentences + which can be understood by ntpd. +
++ First of all i wanted to learn more about DCF77 and gain experience + programming in lua. I also wanted to connect DCF77 to my (Raspberry Pi 2B + based) ntp server without compromising the accuracy of it's already available + PPS signal. When the receiver module looses it's signal it can easily generate + hunderds or thousands of interrupts a second which will definately harm the + PPS accuracy. By moving the processing to an ESP8266 the ESP will take the hit + and just output valid data when it has a decent signal. +
++ It receives data from a DCF77 module and outputs the same data as a GPS would + do. To do that, it has some (IMHO) neat tricks. Usually it will run in an + interrupt driven way, with a clean signal this will trigger twice a second + (one for the rising edge, one for the falling edge). When it detects way more + interrupts than expected, it switches to polling mode. It will use polling to + detect a clean signal, and only when it's clean enough it will change back to + interrupt mode again. +
++ To improve accuracy and reduce the time from the rising edge of the radio + signal to the delivery of the GPS sentence over the serial port it partially + calculates the required checksum for the sentences every minute. Doing so only + leaves the second characters to be added to the checksum. +
++ When a clean signal is received it will blink a led to let you know it's + working. Because LED's can be very bright when it gets dark you can set a + minimum ambient light which will be read from the adc. When the ambient light + is lower it will stop blinking. +
++ Of course you'll need an ESP8266. The ESP32 might actually be compatible, but + i don't know and haven't tested. And of course you'll need a DCF77 receiver + module. The pollin one i have is pretty cheap (around + EUR 10, + ignore the image on the site, it's the conrad module, but you'll get the + pollin one when you order), the popular conrad module might also work but + again: I haven't tested it. +
++ The nodemcu firmware can be build using + their build service. This program + requires the adc, bit, gpio and timer modules. If + you want to use + nodemcu-uploader to + upload the program, be aware that you will also need the file, + node and uart modules. +
++ To use the program upload it to your ESP8266 and if you want it to start + automatically when the ESP is started also upload the init.lua file. Restart + the ESP3288 and then wait :-) +
++ If you look at the code you'll see quite some print statements commented out, + those are there to help debugging. Unfortunately memory on the ESP8266 is too + constrained to be able to uncomment them all at the same time, so use with + caution. +
++ With this you can make ntpd think it's receiving from a GPS while it's + actually using your DCF77 receiver. To do that, first you'll have to instruct + udev to create a gps symlink. I use the following rules in + /etc/udev/rules.d/99-gps.rules: +
++KERNEL=="ttyUSB0", SYMLINK+="gps0" ++
+ After that configure ntpd to use it with a server and fudge line in + /etc/ntp.conf: +
++server 127.127.20.0 mode 0x58 minpoll 3 maxpoll 3 prefer +fudge 127.127.20.0 stratum 0 flag1 0 flag2 0 flag3 0 flag4 0 time1 0.0 time2 0.0292 refid DCF0 ++
+ Especially time2 should be tuned to your own setup. The command ntpq + -pn should now show something like this: +
++ remote refid st t when poll reach delay offset jitter +============================================================================== +*127.127.20.0 .DCF0. 0 l 4 8 377 0.000 -0.214 0.567 ++
+ Have fun! +
diff --git a/dcf77_gps.lua b/dcf77_gps.lua new file mode 100644 index 0000000..e9f24f1 --- /dev/null +++ b/dcf77_gps.lua @@ -0,0 +1,397 @@ +dcf77_pin=6 +led_pin=4 + +min_ambient_light=25 + +last_valid_rise=0 + +valid_rise_min=990000 +valid_rise_max=1010000 +valid_timeout=5000000 + +valid_newmin_min=1990000 +valid_newmin_max=2100000 + +valid_0_min=100000 +valid_0_max=140000 +valid_1_min=200000 +valid_1_max=250000 + +dcfdata="" + +valid_times=0 +total_times=0 + +bcd={} +bcd[1]=1 +bcd[2]=2 +bcd[3]=4 +bcd[4]=8 +bcd[5]=10 +bcd[6]=20 +bcd[7]=40 +bcd[8]=80 + +dow={} +dow[0]="Invalid" +dow[1]="Mon" +dow[2]="Tue" +dow[3]="Wed" +dow[4]="Thu" +dow[5]="Fri" +dow[6]="Sat" +dow[7]="Sun" + +mon_days={} +mon_days[1]=31 +mon_days[2]=28 +mon_days[3]=31 +mon_days[4]=30 +mon_days[5]=31 +mon_days[6]=30 +mon_days[7]=31 +mon_days[8]=31 +mon_days[9]=30 +mon_days[10]=31 +mon_days[11]=30 +mon_days[12]=31 + +function bcd2dec(data) + local value=0 + for count=1,string.len(data),1 + do + if string.sub(data,count,count)=="1" and bcd[count]~=nil then + value=value+bcd[count] + end + end + return value +end + +function check_parity(data) + local onecount=0 + for count=1,string.len(data),1 + do + if string.sub(data,count,count)=="1" then + onecount=onecount+1 + end + end + if onecount%2==0 then + return true + end + return false +end + +gps_sec=0 +gps_valid=false +gps_part1="" +gps_part2="" +gps_part_checksum=0 + +hex={} +hex[0]="0" +hex[1]="1" +hex[2]="2" +hex[3]="3" +hex[4]="4" +hex[5]="5" +hex[6]="6" +hex[7]="7" +hex[8]="8" +hex[9]="9" +hex[10]="A" +hex[11]="B" +hex[12]="C" +hex[13]="D" +hex[14]="E" +hex[15]="F" + +function send_gpsstring() + local gps_data + local gps_checksum=gps_part_checksum + local part1len=string.len(gps_part1) + + if gps_sec<10 then + gps_data=gps_part1.."0"..gps_sec..gps_part2 + else + gps_data=gps_part1..gps_sec..gps_part2 + end + + gps_checksum=bit.bxor(gps_checksum,string.byte(string.sub(gps_data,part1len+1,part1len+1))) + gps_checksum=bit.bxor(gps_checksum,string.byte(string.sub(gps_data,part1len+2,part1len+2))) + + local digit1=bit.rshift(gps_checksum,4) + local digit2=bit.band(gps_checksum,15) + + print("$"..gps_data.."*"..hex[digit1]..hex[digit2].."\r") +end + +function parse_data(data) + total_times=total_times+1 + --print("-------------------------------------------------------------") + --print(data) + --print("Resrv: ",string.sub(data,1,15)) + --print("Info: ",string.sub(data,16,21)) + --print("Min: ",string.sub(data,22,29),bcd2dec(string.sub(data,22,28)),check_parity(string.sub(data,22,29))) + --print("Hour: ",string.sub(data,30,36).." ",bcd2dec(string.sub(data,30,35)),check_parity(string.sub(data,30,36))) + --print("Day: ",string.sub(data,37,42).." ",bcd2dec(string.sub(data,37,42))) + --print("DOW: ",string.sub(data,43,45).." ",bcd2dec(string.sub(data,43,45))) + --print("Month: ",string.sub(data,46,50).." ",bcd2dec(string.sub(data,46,50))) + --print("Year: ",string.sub(data,51,59),bcd2dec(string.sub(data,51,59)),check_parity(string.sub(data,37,59))) + --print("Rest: ",string.sub(data,60)) + --if string.len(data)==59 then + -- print("Time/date : "..bcd2dec(string.sub(data,30,35))..":"..bcd2dec(string.sub(data,22,28)).." "..dow[bcd2dec(string.sub(data,43,45))].." 20"..bcd2dec(string.sub(data,51,59)).."-"..bcd2dec(string.sub(data,46,50)).."-"..bcd2dec(string.sub(data,37,42))) + --end + + gps_valid=false + + local min + local hour + local day + local mon + local year + + if data==nil then + --print("No data received") + return + end + + if string.len(data)~=59 then + --print("Data length invalid") + return + end + --print("Data length valid") + + if string.sub(data,18,18)==string.sub(data,19,19) then + --print("Timezone data is invalid") + return + end + --print("Timezone data is valid") + + if string.sub(data,21,21)=="0" then + --print("Start time bit is invalid") + return + end + --print("Start time bit is valid") + + if not check_parity(string.sub(data,22,29)) then + --print("Minute parity invalid") + return + end + --print("Minute parity valid") + min=bcd2dec(string.sub(data,22,28)) + if min>59 then + --print("Minute value invalid") + return + end + --print("Minute value valid") + + if not check_parity(string.sub(data,30,36)) then + --print("Hour parity invalid") + return + end + --print("Hour parity valid") + hour=bcd2dec(string.sub(data,30,35)) + if hour>23 then + --print("Hour valid invalid") + return + end + --print("Hour valid valid") + + if not check_parity(string.sub(data,37,59)) then + --print("Date parity invalid") + return + end + --print("Date parity valid") + + day=bcd2dec(string.sub(data,37,42)) + if day<1 or day>31 then + --print("Day value invalid") + return + end + --print("Day valud valid") + + mon=bcd2dec(string.sub(data,46,50)) + if mon<1 or mon>12 then + --print("Month value invalid") + return + end + --print("Month value valid") + + year=bcd2dec(string.sub(data,51,59)) + if year<22 or year>30 then + --print("Year value invalid") + return + end + --print("Year value valid") + + valid_times=valid_times+1 + --print("Total "..valid_times.." valid times and "..total_times-valid_times.." invalid times") + + if string.sub(data,18,18)==1 then + --print("Subtracting 1 hour for CET timezone") + hour=hour-1 + else + --print("Subtracting 2 hours for CEST timezone") + hour=hour-2 + end + if hour<0 then + hour=hour+24 + day=day-1 + if day<1 then + mon=mon-1 + if mon<1 then + mon=12 + year=year-1 + end + if mon==2 and year%4==0 then + day=day+1 + end + day=mon_days[mon] + end + end + gps_part1=string.format("GPZDA,%02d%02d",hour,min) + gps_part2=string.format(".000,%02d,%02d,20%02d,,",day,mon,year) + + local gps_data=gps_part1..gps_part2 + gps_part_checksum=0 + + for count=1,string.len(gps_data) + do + gps_part_checksum=bit.bxor(gps_part_checksum,string.byte(string.sub(gps_data,count,count))) + end + + gps_sec=0 + gps_valid=true + send_gpsstring() +end + +function irq_handler(level,when,count) + if count>10 then + --print("Waiting for stable signal, changing to polling") + start_poll() + return + end + if when