‰  NOW 20 WPM  ‰  TEXT IS FROM OCTOBER 2018 QST  PAGE 41‰

THE ACTIVATE TIME IS ABOUT 6 MS AND THE DEACTIVATE TIME IS ABOUT 4 MS.
WITH R39/D1 IN PARALLEL WITH R38, THE ACTIVATE TIME WAS REDUCED TO 4 MS AND
THE DEACTIVATE TIME REMAINS AT 4 MS.  IN THIS CIRCUIT, U3A IS USED AS A
VOLTAGE DETECTOR AND LATCH.  WHEN THE VOLTAGE ON C12 GOES BELOW 1/3 OF THE
SUPPLY VOLTAGE 1R67 V DC, THE INTERNAL LATCH WITHIN U3A IS CLEARED AND THE
OUTPUT OF U3 GOES HIGH, AND TRANSISTORS Q1 AND Q2 ARE CONDUCTING ON.  WHEN
THE VOLTAGE ACROSS C12 IS GREATER THAN 2/3 OF THE SUPPLY VOLTAGE 3R33 V DC,
THE INTERNAL LATCH WITHIN U3A IS SET AND THE OUTPUT OF U3A GOES LOW,
CAUSING Q1 AND Q2 TO BE IN CUTOFF OFF.  WHEN THE VOLTAGE ON C12 IS ANYWHERE
BETWEEN 1/3 AND 2/3 OF THE SUPPLY VOLTAGE, THE OUTPUT OF U3 STAYS IN THE
SAME STATE AS IT WAS THE LAST TIME WHEN THE VOLTAGE ON C12 WAS EITHER LESS
‰  END OF 20 WPM TEXT  ‰  QST DE W1AW  ƒ