A bargraph or mobile bar indicator with 4 LEDs can be implemented by connecting the 4093 NAND gates as voltage comparators. The circuit in the figure shows how this can be done. The resistor network from R2 to R5 determines the trigger point of each LED, and the values of these components can be changed, depending on the application. The indicators are common red LEDs and the voltage. The circuit is powered with voltages from 6 to 12 V. When the circuit is powered, capacitor C1 starts to charge slowly so that the voltage at the input of the bargraph indicator rises slowly, the LEDs light up one by one until completes the timing. The setting of P1 and the value of C1 determine the speed with which the timing occurs. Maximum values of P1 are around 100 k ohms and for C1, 1,500 uF which results in a delay of a few minutes. To start a second time delay, wait a few seconds for capacitor C1 to discharge. The value of R5 determines the sensitivity of the circuit and must be changed if the rise does not occur until the end of the scale (four LEDs lit).
