How to make a a circuit to receive and decode  AM/FM broadcasted time of day - Page 1
Forum section: electronics / projects

author: SuzyC
author_rank: Frequent Contributor
timestamp: October 10, 2015, 01:58:25 am
content: I have seen cheap LCD clocks being sold locally that somehow receive the current time for automatic clock time setting.Anyone know how to do this easily and cheaply and simply?

author: kc8apf
author_rank: Regular Contributor
timestamp: October 10, 2015, 02:13:57 am
content: WWVBis a common method in the US.DCF77is a similar system from Germany. I'm not aware of a standard for including the timecode in an AM or FM broadcast.

author: janoc
author_rank: Super Contributor
timestamp: October 10, 2015, 02:19:09 am
content: They most likely have a simple DCF77 receiver inside (if sold in Europe). There are similar stations broadcasting time signals all over the world.You can find some info here:https://en.wikipedia.org/wiki/DCF77https://en.wikipedia.org/wiki/Radio_clockI believe you can also get time from FM radio from the RDS signal, but not every stations carries that info. And probably such system wouldn't be too practical for a mass market clock, due to the relatively short range of the VHF FM radio signals - the clock would need to be tuned at the place of its installation. This is more common in car radios and better stereos - they will set their clock if they get a good RDS signal.

author: SuzyC
author_rank: Frequent Contributor
timestamp: October 10, 2015, 02:33:37 am
content: I bought an automatic time set clock at the local Walmart and tore it apart a few seconds after getting it home and found inside a loopstick feeding a black blob IC that does the job.Problem is, although the time is clearly visible on the LCD after a few minutes after powerup, there seems no way to extract the time data from this very cheap realtime solution, except perhaps by somehow hacking the LCD signals..not so simple a task.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 10, 2015, 02:44:57 am
content: This page sums up the "state of the art" pretty well...http://www.kb6nu.com/how-to-build-a-wwvb-receiver/There used to be a small module kit with the ferrite loopstick and a small PC board with the circuit.But apparently not available anymore....

author: SuzyC
author_rank: Frequent Contributor
timestamp: October 10, 2015, 03:05:14 am
content: Seems that LW time receiver modules are not cheap or easy to find for a reasonable price. The only one I saw on the net sold for about 10x the cost of the Walmart and was regionalized for sale only in the USA.Since there are many cheap and very fast op-amps that have considerable voltage gain in the MHz, would it be so hard to construct a 60KHz time signal receiver around an op-amp stage or two using the Loopstick included in my Walmart master timepiece?Once the time signal serial bitstream is made available the C-code for constructing a decoder/clock with a PIC chip is available on the web.

author: pickle9000
author_rank: Super Contributor
timestamp: October 10, 2015, 03:07:42 am
content: Quote from: Richard Crowley on October 10, 2015, 02:44:57 amEbay has em.http://www.ebay.ca/sch/pv.electronics/m.html?item=231651545481&hash=item35ef821189&rt=nc&_trksid=p2047675.l2562

author: SuzyC
author_rank: Frequent Contributor
timestamp: October 10, 2015, 03:13:18 am
content: Fascinating, the Ebay module offered are available at a cost about 5X the Walmart table clock complete.I still am thinking of using the loopstick with op-amps as TRF gain stages..could it be done, or could this be dumb?

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 10, 2015, 03:14:59 am
content: Quote from: SuzyC on October 10, 2015, 03:05:14 am"Regionalized" because the radio-time signals themselves are "regionalized". A receiver made for WWVB won't work for DCF77 and vice-versa.QuoteThere are people who make their own RF front-end very similar to that ferrite loop-stick, and then use a micro-controller (most famously Arduino) to actually decode the pulse-stream into date and time information.Of course, you should confirm which station you can get, and how strong the signal is. You have not revealed your location, so we can only guess that you are somewhere in North America (reference to Walmart?) In Canada and the north-east US, CHU may be a better signal.

author: SuzyC
author_rank: Frequent Contributor
timestamp: October 10, 2015, 03:18:21 am
content: Many thanks for all replies!Walmart became an international company in 1991, and has stores in 26 countries outside the United States.I already seemed to have purchased the loopstick, it comes free with the Walmart clock, so why not use this loopstick to make a TRF receiver with op-amps as TRF gain stages..could it be done, or could this be dumb?http://www.joejaworski.com/wwvb/shows full PIC source code and complete construction details to otherwise make the clock tick!

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 10, 2015, 03:24:29 am
content: Dunno.Which time/date/frequency standard station(s) are you within range of? How strong is the signal?Keeping your location secret means we can offer only broad general responses.You will have to do your own research to see what is available in your area.

author: ralphd
author_rank: Frequent Contributor
timestamp: October 10, 2015, 04:10:06 am
content: Quote from: kc8apf on October 10, 2015, 02:13:57 amThere is a standard for weather data over FM. I think it includes time/date too. The standard is used in US & Canada. Not sure about elsewhere in the world.Don't have a link saved, but some modest google-fu should find it.

author: SuzyC
author_rank: Frequent Contributor
timestamp: October 12, 2015, 03:55:48 am
content: Thanks again for all replies!The Walmart LCD clock is only synchronized from time to time to the broadcast time, so the only crystal/resonator/filter I see on the PCB is probably used for counting down to get a second tick, I see only a 32...KHz tiny cylindrical xtal on board. There are visible many other tiny SMD caps and resistors on the PCB, but no other resonators. Tayloe-Smayloe, I don't need no stink'n Tayloe detector!I am thinking along the lines of loopstick with parallel capacitor for the antenna/resonant element fed to an op-amp gain stage followed by a bandpass filter (aka notch filter) and schottky diode half-wave detector to recover the serial timecode stream to feed into a PIC MCU. The world is a noisy place at these low frequencies, but the amount of circuitry and complexity of building a superhet is a bit much. To deal with the noise, the entire bit stream is decoded by the MCU and since time and date and year are sent along with dedicated fixed bit values, it is easy enough to tell if the received time is valid or corrupted by noise.

author: mark03
author_rank: Frequent Contributor
timestamp: October 12, 2015, 03:55:35 pm
content: Just make sure you check the date on web sites describing the WWVB modulation and how to decode it. They made a big change to the broadcast format a few (?) years ago. Google for the details, but IIRC they did preserve backwards compatibility with cheap "atomic clock" receivers; however, they also added a PSK component which should allow decoding at lower signal strength. This was controversial because it broke existing WWVB frequency standards, but you'd have to be a time-nut to care about that(add site:febo.com to your search for plenty of relevant discussion).

author: cezar
author_rank: Contributor
timestamp: October 12, 2015, 04:11:22 pm
content: there is also a transmitter in the UK :http://www.npl.co.uk/science-technology/time-frequency/products-and-services/time/msf-radio-time-signalAlso, many radios (especially those installed in cars) synchronize their clocks with time being transmitted with RDS signal. Accuracy of RDS CT is "100" ms but its enough for this purpose.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 12, 2015, 05:10:38 pm
content: Quote from: mark03 on October 12, 2015, 03:55:35 pmWhile @SuzyC steadfastly declines to reveal his/her location, s/he give the impression of a location outside North America.Since we don't know which source is being discussed, we are limited to generic responses.