=  NOW 25 WPM  =  TEXT IS FROM FEBRAURY 2023  QST  PAGE 34 =

M INPUT RESISTOR AND THE 1 M FEEDBACK RESISTOR.  A SECOND OP AMP IS USED AS
A DIVIDER FOR THE POWER SUPPLY AND GENERATES AN ARTIFICIAL GROUND.  IF THE
BATTERY IS 9 V, THE GROUND WILL BE AT ONE HALF OF THIS, OR 4R5 V.  THIS IS
NECESSARY, AS THE INPUT AMPLIFIER WILL INVERT THE SIGNAL AND THE OUTPUT
SWING WILL BE A NEGATIVE VOLTAGE REFERENCED TO THIS GROUND.  I CONSTRUCTED
THIS VIA POINT TO POINT WIRING ON PERF BOARD MOUNTED TO THE BACK OF THE
METER.  ONLY DC SIGNALS ARE PRESENT, SO WIRING IS NOT CRITICAL.  THE
DIGITAL MEASUREMENT METER CIRCUIT SEE WWW. ARRL. ORG/ QST IN DEPTH, WITH
THE FRONT FACE SHOWN IN FIGURE 3, EMPLOYS AN ARDUINO NANO MICRO CONTROLLER
TO INCREASE ACCURACY.  THE NANO HAS SEVERAL ANALOG INPUTS THAT ARE 10 BIT
SAR DCS.  EVEN THOUGH THE INPUT RESISTANCE IS SEVERAL M, THE IMPEDANCE OF
THE ANALOG INPUT MUST BE LESS THAN 10 K.  THIS IS BECAUSE ONE INPUT IS
SAMPLED AT A TIME THROUGH AN ANALOG SWITCH, AS USED BY THE SAR.
=  END OF 25 WPM TEXT  =  QST DE W1AW  <