Multiple PIC's, one OSC.
Harold M Hallikainen email (remove spam text)
On Wed, 13 Oct 1999 22:19:31 -0400 "Sean H. Breheny" <CORNELL.EDU> shb7
This reminds me of the old weather map fax machines I used to
work on for the FAA. They used soggy paper and passed current thru the
paper to turn a pixel brown. The paper was pulled over a drum that
rotated with a helix contact on it. There was also a contact band above
the paper. As the drum rotated, we got a horizontal scan across the
page. The motion of the paper gave the vertical scan. At the beginning
of each map was a black bar with a white horizontal sync pulse. On
detecting this, the oscillator that drove the synchronous motor driving
the helix drum changed from 60 Hz to 59 Hz or so. The motor would
continue to run at this speed until a magnetic reed switch on the side of
the drum closed during the received sync pulse, indicating the sync pulse
was now at the edge of the picture. The motor then changed back to 60
Hz. At the top of each map was this black bar with a white diagonal
stripe going down and to the left until it hit the left end of the paper.
The oscillator for the motor was a crystal oscillator with a
digital divider chain. As I recall, they changed the digitial division
ratio to slow the motor down. The oscillator/divider chain then drove a
big transistorized power amp that drove the motor. The only problems we
EVER had with the machine were due to the power amp blowing up.
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm
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