=  NOW 20 WPM  =  TEXT IS FROM FEBRAURY 2023  QST  PAGE 34 =

MEASUREMENTS ARE IN MICROSECONDS, AND ARE AFFECTED BY THE INTERNAL
CAPACITANCES.  THE OUTPUT IMPEDANCE OF AN LM324 OP AMP IS LOW AND CAN
EASILY DRIVE THE MICROCONTROLLER.  A 0R001 F CAPACITOR ELIMINATES ANY RF.
A GENERAL PURPOSE SILICON RECTIFIER IS IN SERIES WITH THE 9 V BATTERY
NEGATIVE TERMINAL IN ORDER TO OBTAIN A SMALL NEGATIVE VOLTAGE FOR THE OP
AMP.  ONE SECTION FROM THE LM324 IS USED IN THIS CIRCUIT AS A VOLTAGE
FOLLOWER FOR THE INPUT DIVIDER.  A VOLTAGE FOLLOWER HAS A HIGH INPUT
RESISTANCE AND DOES NOT LOAD THE DIVIDER.  THE OUTPUT LEVEL OF THIS STAGE
IS APPLIED TO A TRIMMER THAT IS USED FOR CALIBRATION.  IT IS IMPORTANT FOR
THE ANALOG VOLTAGE APPLIED TO THE NANO TO BE BETWEEN 0 V AND 5 V, AS
VOLTAGES OUTSIDE OF THESE LIMITS CAN DESTROY THE MICROPROCESSOR.  ARDUINO
=  END OF 20 WPM TEXT  =  QST DE W1AW  <