40 Segment LED S-Meter
To Calibrate:
Provide your radio with a very string signal, then adjust the HIGH LEVEL pot to
the threshold of illuminating the last LED (all LEDs on).
Remove the signal completely, then adjust the LOW LEVEL pot to the threshold of
no LEDs illuminated.
If your radio's S-meter output is greater than 5 volts, you mau wish to replace
the HIGH LEVEL pot with a 10K resistor, and provide pin 6 of the right-most 3914
with the cathode of a 6.1 volt zener diode, pulled up to 13 volts with a 1K
resistor. The anode should be connected to ground. You may use a higher voltage
zener if necessary.
This configuration provides 10ma per LED segment. Change the values to the
resistors and pots to change the drive current to the LEDs.
R1=12.5/I R2=25/I R3=37.5/I R4=50/I where I = the desired LED current
By: N6ZAV Marty Mitchell