The four gates of the 4093 are connected as voltage comparators. A resistor network Wired to the input of the gates acts as a voltage divider, determining the moment in which each output goes low and turns on the corresponding LED.
Different values of resistors in the voltage divider are used to obtain a linear response as the capacitor charges through the timer resistors according an exponential characteristic.
A schematic diagram of the Four-LED Bargraph Timer is shown in Fig. 1.
IC1 - 4093 CMOS integrated circuit
LED1 to LED4 - Red common LEDs
R1 - 100,000 ohm - potentiometer
R2 - 10,000 ohm, 1/4 W, 5% resistor
R3 - 47,000 ohm, 1/4 W, 5% resistor
R4 - 33,000 ohm, 1/4 W, 5% resistor
R5 - 22,000 Ω, 1/4 W, 5% resistor
R6 - 330,000 Ω, 1/4 W, 5% resistor
R7 to R10 - 1,000 ohm, 1/4 W, 5% resistor
C1 - 100 µF to 1,000 µF, 12 WVDC electrolytic capacitor
C2 - 100 µF, 12 WVDC electrolytic capacitor
