‰  NOW 25 WPM  ‰  TEXT IS FROM JANUARY 2017 QST  PAGE 47‰

PHOTO COUPLER, AND THROUGH THE APPROPRIATE SET OF NORMALLY CLOSED LIMIT
SENSORS ON THE MAST.  THE OPTICALLY COUPLED TRANSISTOR IN Q1 CONDUCTS, AND
CLOSES RELAY K2, WHICH CUTS POWER TO THE LIMIT LED INDICATOR.  AS SOON AS
ANY LIMIT SWITCH IS TRIPPED, THE POWER RELAY COIL CIRCUIT IS INSTANTLY
OPENED, CUTTING POWER TO THE MOTOR.  THIS CAUSES K2 TO OPEN, WHICH APPLIES
POWER TO THE RED LIMIT LED INDICATOR ON THE FRONT PANEL.  S3B IS USED TO
OPEN THE LIMIT INDICATOR CIRCUIT WHEN SWITCH S3 IS RETURNED TO THE STOP
POSITION.  THE REST OF THE CONTROL CIRCUIT IS RELATIVELY STRAIGHTFORWARD.
THE RASPBERRY PI MODEL B IS A TINY, FULL FLEDGED COMPUTER.  I CAN CONNECT A
KEYBOARD, MOUSE, AND DISPLAY TO EDIT THE PROGRAMMING ON THE FLY.  LIKE A
LARGER COMPUTER, IT HAS A BOOT STARTUP CYCLE AND LIKES TO BE SHUT DOWN
GRACEFULLY.  THERE ARE OTHER MICRO CONTROLLERS SUCH AS THE ARDUINO OR
STANDALONE CHIPS THAT MIGHT BE BETTER CHOICES FOR AN EMBEDDED CONTROLLER.
‰  END OF 25 WPM TEXT  ‰  QST DE W1AW  ƒ