On Nov 12, 2007, at 10:14 PM, Eric Lemmon wrote: > Nate, > > I appreciate your suggestions and comments, even though we have > differing > opinions about accuracy. In my area, starting an ARES or MARS net a > minute > or two early or late is not acceptable. We pride ourselves at > beginning the > net exactly on the second. After all, we're Hams, and we have > access to > WWV, don't we? I realize that some folks on this forum may be > rolling their > eyes at that statement, but hey- if sloppy operating is okay with > them, let > them do their thing!
But you don't need the controller involved in that. Just punch a few digits to put the controller in Net mode (if that's why the controller needs to be accurate), and call the Net on-time! :-) *BIG GRIN* > My obsession (yes, that's probably what it is!) with time accuracy > began [snipped story for space..] Very cool. I also like that type of thing. I've been looking into how to modify existing OXCO's into an accurate GPS-locked 10 MHz source for the test gear in the ham shack. There's LOTS of information about how to do that "out there", I'm still just in the "browsing" stage of the project... something to do this winter, I suppose. There have been good articles in QEX, and there's a number of others online. Some of these folks are pretty hard-core, when they're measuring the accuracy of the GPS system itself, and showing when it's nano-seconds off on a particular day... a whole hobby unto itself, really. (An inordinate number of hams involved in those projects, too. Kinda neat.) > With this background information, perhaps you can understand that > all I > really need is some signal that occurs at exactly some point in > time, every > day, that can be used to synchronize a repeater controller > automatically. > Most real-time clock chips, including those made by Dallas > Semiconductor, > have sufficient short-term accuracy to "flywheel" through one day > without > getting more than a second off. If I can tweak such a clock once a > day to > bring it to the exact time, that is enough. I really don't want to > add > phone lines, IRLP links, wireless networks, or anything else to make > this > happen. Yep. I think the once-a-day or once-a-week thing with a transmitter and a central WWV-based solution with a microcontroller would be a piece of cake, for the type of accuracy (one second) you're looking for. Again, lots of projects out there that already drive real clock displays... you just need to teach the micro to kick off a routine however-often-you-like that sets the controller remotely via DTMF. In fact, now that I think about it, you don't need the transmitter at all... just stuff the audio output of the board into a receiver port on the controller at the site. To be honest, it's probably easier to do it with a GPS and NMEA output these days, and less chance that you won't be hearing WWV on a particular day. > It would be great if the next-generation repeater controllers had a > BNC or > TNC connector on the back labeled "GPS antenna" or "WWVB antenna" > and all I > needed to do was install one simple antenna, and the controller > would know > the time! Yeah, Ken mentioned that he's adding that to his controllers today here on the list, and I bet others who have serial ports on their controllers are reading along... not too difficult to find code already written that will read 4800 baud or 9600 baud NMEA strings going by and pick off the time-stamp. That's all the little clock projects done by lots of electronics hobbyists out there have done... Here's an Atmel clock, complete with schematics and code, to start with... http://www.rentron.com/at89c205.htm (It even uses a Dallas chipset "freewheeling" as you mentioned, which is why it caught my eye.) Then mix in portions of something like this, the Atmel DTMF dialer: http://www.circuitcellar.com/avr2004/wabstracts/A3713abstract.pdf Get the code running on a single AVR, and once you have the prototype working, draw it up as a board in Eagle, or even something proprietary like PCB123, send off for a $20 board, solder your toys on, and you've got your daily clock setter board! :-) That was just stuff I found with a quick Google. There's better designs out there for the clocks... Of course, the same things can be done with a Microchip PIC Microcontroller. Or the TI MCP430 type controllers... or... the list goes on. The Atmel and PIC are probably the most commonly seen in hobbyist electronics. http://www.avrfreaks.net http://www.piclist.com They're actually quite a bit of fun... if you remember programming 8- bit computers in any way years ago, it's virtually the same thing -- the only difference being, you have to design the interfaces to the "real world" (transistor switches, or stay within the limits of the chip's ability to sink or source current on the pins) yourself, and the whole thing fits on a single chip. (In fact, sometimes it's getting difficult to find the chips in DIP packaging, and you may have to learn to do a little surface-mount soldering if you haven't done that before, to get the chip you want, onto your board. Google "toaster oven reflow machine" sometime for some ingenious ways to turn a $20 toaster oven into a backyard solder- reflow machine for surface-mount boards!) For many applications, the on-board RC clock circuit is accurate enough for 9600 baud serial communications (although most folks use a ceramic oscillator or crystal to clock the microcontroller instead, you don't really have to in all applications -- site temperature would be an important design consideration here) and the little chip can be the "brains" to do just about whatever you want. Depending on how easy you find Assembly programming, if you don't like that and want a higher-level language, there are free and commercial (not all that hideously expensive) C and BASIC compilers for these chips also. Most of the modern chips can be re-flashed/programmed serially via a cheap $30 programmer than can program the chips in- circuit (as long as the circuit is designed so the programming pins are available to the programmer properly), and some can even do in- circuit debugging, using the chip as a driver for stepping through your code, one processor command at a time, so you can find a timing or other glitch? That's REALLY cool... hook a couple of wires as a serial connection to a chip running in-circuit, and ask it to single-step the code it's running... for $30? Amazing. Most of the "modern" repeater controllers are using either PIC's or Atmel's... learning this stuff means you can build your own repeater logic or other logic circuits into a single chip, and have complete control of how that logic behaves if you want to change it... very inexpensively. High-end controllers just scale this up into fancier/ more-intelligent chips... or FPGA's.. etc... they also pay attention (well hopefully) to all the analog behaviors of their circuit so as not to color the audio, etc... stuff you might have to tinker a bit with if making something of your own... convenience vs. shell out some bucks. By the way, I'm sure there are those on this list that would love this... and could build this a LOT cheaper... but if you haven't had any "fun" with electronics in a while, some of the gadgets at sparkfun.com are great... right at the moment, this is my favorite: <http://www.sparkfun.com/commerce/product_info.php?products_id=287 > Stick a GSM SIM card in it, and you have an instant wireless Commissioner Gordon style, Bat Phone! LOL! I love it. Not going to pay that price for it, though! Heh... time to find a GSM phone to gut for that project this winter... -- Nate Duehr, WY0X [EMAIL PROTECTED]
