Olin Lathrop wrote: > Tony Pan wrote: > > I really need to design a product that knows the official U.S. time, > aside > > from other features. Can someone tell me what is required for the > hardware > > and software to acquire the official time? And what kind of connections > are > > required? Olin, you need an email client that doesn't try to re-wrap your quotes; it's *really inconvenient* for those of us who want to reply to you... Also, you should include an attribution line like the one I inserted above. > If the gizmo already has an internet connection, then the contacting a > NNTP server requires no additional hardware. I think you mean NTP or SNTP; NNTP is for Usenet news. However, beware of releasing a horde of products that all pound on one preconfigured (S)NTP server; you'll get its owner upset. > 2 - Decode the WWVL long wave broadcasts. It's WWVB, on 60 kHz. There are similar services in other regions. > 3 - Decode WWV broadcast. These are at several shortwave frequencies. > I know 10MHz is one of them, and I think there are also broadcasts at > 2.5MHz, 5MHz, and 15MHz, but I'm not sure. These may be more difficult to > decode, but the coverage should be wider. I'm not totally sure they even > have encoded data on them. Yes, they do. It's the same data as on WWVB, encoded on a 100 Hz audio subcarrier. You can hear it below the tones, clicks and voice announcements if you have a shortwave receiver with decent bass response. I don't think they broadcast on 2.5 MHz any more; just 5, 10 and 15 MHz. > 4 - Canada also broadcasts a time standard. The radio station is called > CHU if I remember right. I don't know whether it contains coded > information that a micro can use. Yes, it does -- a Bell-103 compatible (300 baud) modem signal in seconds :31 through :39 of each minute. CHU broadcasts on 3.330, 7.335 and 14.670 MHz. I wrote a 2-part Circuit Cellar article on decoding this signal in a DSP. Unfortunately, it isn't available online, but you can follow this link if you want to look it up: http://www.dtweed.com/circuitcellar/xtweedda.htm ========== So, to summarize, you can go with wired or wireless. Wired options include a modem or LAN connection, or direct connection (e.g., RS-232) to another device that knows what time it is. Wireless options include longwave, shortwave, GPS, and certain TV channels (e.g., PBS stations, although accuracy on these can be pretty spotty). I think you can also get the time of day in the RDS subcarrier on certain FM broadcast stations. You need to think about which of these fit in well with the other functions and requirements of the product. -- Dave Tweed -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu