piclist 1999\10\27\064629a >
Thread: Synchronised clocks
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<DIV><FONT size=2>Hello helpful all.</FONT></DIV>
<DIV><FONT size=2>I'm starting the last stage of a project which needs two
<DIV><FONT size=2>count-down clocks. Think I know how I'd like to do it but
would appreciate </FONT></DIV>
<DIV><FONT size=2>any </FONT><FONT size=2>thoughts members have.</FONT></DIV>
<DIV><FONT size=2>Each clock is built around an F84</FONT><FONT size=2>.
</FONT><FONT size=2>Readout </FONT><FONT size=2>is a 4-digit 12mm </FONT><FONT
size=2>LCD, </FONT></DIV>
<DIV><FONT size=2>showing either Hh:Mm or Mm:Ss. The two clocks </FONT><FONT
size=2>are separated </FONT><FONT size=2>by 30 </FONT></DIV>
<DIV><FONT size=2>feet. They are identical except that one is a </FONT><FONT
size=2>master, </FONT><FONT size=2>the </FONT><FONT size=2>other a slave.
<DIV><FONT size=2>The slave</FONT><FONT size=2> needs to start with whatever
time is set on the </FONT><FONT size=2>master. </FONT><FONT size=2>It
<DIV><FONT size=2>should also Pause/Unpause or Reset when told to by the master.
The </FONT></DIV>
<DIV><FONT size=2>necessity </FONT><FONT size=2>is </FONT><FONT size=2>for
one-way IR communication&nbsp;from master to slave. One </FONT></DIV>
<DIV><FONT size=2>possibility which </FONT><FONT size=2>may foul this up from
time to time is coinciding IRQs</FONT><FONT size=2>.</FONT></DIV>
<DIV><FONT size=2>&nbsp;</FONT></DIV>
<DIV><FONT size=2>The plan is to have the master&nbsp;enable its Timer0 IRQ
first</FONT><FONT size=2> and the slave </FONT></DIV>
<DIV><FONT size=2>only enable its&nbsp;IRQ after receiving the first
</FONT><FONT size=2>pulse of IR </FONT><FONT size=2>from the master. The
<DIV><FONT size=2>slave would&nbsp;delay about 1/2 an IRQ period, </FONT><FONT
size=2>so that the IRQs of </FONT><FONT size=2>the master </FONT></DIV>
<DIV><FONT size=2>and slave are well and truly </FONT><FONT size=2>separated in
time.&nbsp;A</FONT><FONT size=2>s each digit is </FONT><FONT size=2>in the range
<DIV><FONT size=2>0-9 </FONT><FONT size=2>I could send a&nbsp;wake-up pulse of 2
IRQs </FONT><FONT size=2>length and then </FONT><FONT size=2>4x4-bit
</FONT><FONT size=2>nybbles, </FONT></DIV>
<DIV><FONT size=2>using </FONT><FONT size=2>1bit per IRQ. Both clocks would then
</FONT><FONT size=2>start their count-</FONT><FONT size=2>down as </FONT><FONT
size=2>soon </FONT></DIV>
<DIV><FONT size=2>as the IR </FONT><FONT size=2>transmission had finished. The
time </FONT><FONT size=2>difference </FONT><FONT size=2>between the </FONT><FONT
size=2>displays </FONT></DIV>
<DIV><FONT size=2>would be </FONT><FONT size=2>the 1/2 IRQ. </FONT><FONT
size=2>Pause/Unpause&nbsp;and </FONT><FONT size=2>Reset </FONT><FONT
size=2>could be </FONT><FONT size=2>1010 </FONT><FONT size=2>and
<DIV><FONT size=2>Is there anything glaringly obvious I've overlooked
<DIV><FONT size=2>The IR receiver has been taken from a trashed VCR. I've tried
a few discrete </FONT></DIV>
<DIV><FONT size=2>designs in the past but never managed to come up with anything
as effective.</FONT></DIV>
<DIV><FONT size=2>Although the power consumption is sort of OK at 1.5mA at 5V
(the slave</FONT></DIV>
<DIV><FONT size=2>clock is on&nbsp;battery power), if anyone knows </FONT><FONT
size=2>of </FONT><FONT size=2>a circuit as good </FONT><FONT size=2>as a VCR
<DIV><FONT size=2>receiver at lower power I'd be interested.</FONT></DIV>
<DIV><FONT size=2>regards, Joe</FONT></DIV>
<DIV><FONT size=2>PS there's a printer utility called FinePrint that will
condense several pages </FONT></DIV>
<DIV><FONT size=2>onto </FONT><FONT size=2>one sheet. I've used it for a while
to save paper when printing listings. 4 </FONT></DIV>
<DIV><FONT size=2>pages </FONT><FONT size=2>per sheet is&nbsp;about the limit of
readability. I found it at download.com </FONT></DIV>
<DIV><FONT size=2>under </FONT><FONT size=2>Utilities /


See also: www.piclist.com/techref/timers.htm?key=clock
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