Notes and misc items re: GPS Analoque Clock Project 04203091, that
   appeared in the magazine SILICON CHIP - 2009 - March

Hi Bob,

1. First of all, thanks for correcting the 5v & 3v 'jumper' pin selector
   just a bit 'south' of the MAX 756 on the overlay, as I pointed out 
   earlier, or contructors would have or could have blown up their EM408 
   with the 'WRONG' voltage as diagram is shown in the magazine, I have 
   also notified Silicon Chip of this oversight, and you can purchase 
   those IC's from FUTURELEC.com (up Newcastle way)

   And the unit can work off an ordinary 16F88, but I know it will be random
   chaos as the 2 x 1.5v AA Batteries get 'lower' in volts, as the ordinary
   16F88 cannot hope to match the 'LOWER VOLTAGE' capability of the 16LF88.

2. I want to let you know I found a program bug in the PIC program for  
   the GPS clock. If you fire up the clock between about 9:06 and 12:00  
   (am or pm) the hands won't move. This is due to an arithmetic overflow  
   in the variable that calculates how many seconds to step forwards,  
   which makes it exceed 32767, and become negative. (10 am = 10 * 60 *  
   60 seconds = 36000, which exceeds 32767).

   Of course, the author recommends powering it up shortly after 12, in  
   which case you won't have the problem. However constructors may be  
   dismayed if they finish construction at 10 am, and turn it on, to find  
   nothing happening.

3. I have notified Geoff Graham (the author) of the problem, and have yet 
   to have his confirmation. However I am pretty sure I am right, as 
   yesterday the clock wouldn't work when I tried it at 10:30 am, but, 
   without any changes, worked just after 12 noon.

   (comment from RCS, maybe it was waiting for a new work place agreement)

4. When you are shipping boards or PIC chips you may want to include a 
   note warning of this problem, or wait for a corrected program for  
   programming the chips.  It is no big deal, as powering the clock up at  
   10.oo am means it will spend practically a day trying to catch up, so it  
   is much better to wait 2 hours and power it up after 12.

5. My observations are, that when powering up the clock the very first  
   pulse seems to be lost as the hands just tremble and don't move. I am  
   guessing that the stepper motor has received two +ve pulses, and thus  
   discards the second one. After that it gets -ve, +ve and so on, and  
   moves normally. Thus the clock is instantly one second slow, from  
   which it never recovers.

   Trying to stop the clock when the hands are back at 12, and starting  
   again doesn't help, as it receives an even amount of pulses to do  
   that, and the problem repeats itself.

   My theory is, that to correct this, the only simple way is to reverse  
   the polarity of the wires to the stepper motor, as I guess the circuit  
   always starts off with a pulse in a certain direction, and if the  
   magnet in the motor is the wrong way around for that pulse, it will  
   always discard the first pulse.

   So, my suggestion to constructors is, if on powering up, you observe  
   the first pulse does not move the hands, wait until the second hand is  
   back at 12, reset the minute and hour hands, and then reverse the  
   wires to the stepper motor (and re-power up the circuit). 
   After that it should work consistently.

   Regards, Nick G. 3079

   RCS Comment, we will notify purchasers/contructors to look at this 
   web page before plugging in the batteries or using a 5v Power Supply
   or . . . . ' the smoke will escape out of this project', and any 
   project in which the smoke escapes is usually 'fatal or terminal'.

   The above comments are "hand's on" so his hints and findings are to be
   noted and responsible appreciation of 'debugging' this very involved
   technical project, yes, the key is the EM408, but this very technical 
   and delicate electronic item must be respected for its ability to extract
   literally microvolts (pico volts even) of signal and then decrypt/decode 
   and use it to create a data stream is truly to me an old 'radio' nutter
   quite an incredible achievement.

   Whilst some of 'MY' (RCS) comments may appear sarcastic, they are not 
   meant to slur the author, only just my old 'modis opperendi' creeping 
   from my old tech sgt. ways of what seems many thousands of years ago. 

   - - -

   end of 04203091.txt file found on  >>>  http://www.rcsradio.com.au
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