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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
This page by Byon Garrabrant N6BG [email protected] 12/24/97