CD 4011 Astable


CD 4011 contains four 2-input NAND gates in a single package. All the gates are independent in operation except for the common power supply and ground. CD 4011 comes in the 14 pin DIP (Dual In Line Package). Unlike other digital integrated circuits, all the unused inputs of the IC should be either connected to the positive rail or ground. No inputs should be left floating as this may cause erratic operation of the IC.


The circuit shown below is a simple oscillator using CD 4011 and only few passive components. This forms a simple RC oscillator. Resistor R2 (18K) turns gate 1(N1) into a linear amplifier with positive feed back. The circuit can give 2.2 kHz pulses from pin 4.

The formula to determine frequency is

Frequency of Oscillation f = 1 / 2.5 x R2 x C1

R2 = 18 K ( 18x 10 3 ) C1 = 0.01 ( 0.01x 10 -6 )

f = 1 / 2.5 x 18 x 10 3 x 0.01 x 10 – 6

1 / 2.5 x 0.18 x 10 -3

= 2.2 kHz



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