Polished Logarithmic Timer Circuit, Feature : Durable

Logarithmic Timer provides an effective way to show the periods of 5 to 15 minutes using ten LED display. Logarithmic Timer is based on the display driver IC1. The display is in the form of ten LEDs, which glows one by one or dot mode, indicating the lapse of time. Logarithmic Timer is also possible to show the display in bar mode through toggle switch S2.
About the Circuit :
IC1, which is display driver IC has logarithmic scale. The resistor network R6-P1-C1 is used for time measurements. The voltage across this network has while C1 is being charged an exponential character when this is applied to IC1, which takes its logarithm. The time is shown linearly on the display. The values of P1 and R6 have been chosen to enable the timer showing periods of 5 to15 minutes.

The timer is reset (C1is discharged) when S1 is closed. Resistor R1 limits the peak value of the discharged current from C1 to an acceptable value for the switch contacts.
Resistor R5 compensates the leakage currents of the electrolytic capacitors to obviate the risk of D10 going out.
If S2 is open, the display is in the dot mode. The elapsing of time is then shown by only one LED light. After a reset, D1 will light and then sequentially all other LEDs.
The total current drawn by the timer is 20mA, so the battery supply is possible. When S2 is ON, the display is in the bar mode. After a reset, all LEDs will light and then go out in turn, starting with D1. In this mode, battery supply is not recommended.