Fig. 1 CD4047 Monostable Mode Multivibrator circuit.

# CD4047 Monostable Multivibrator Circuit

by Lewis Loflin

A Monostable Multivibrator is defined as:

Monostable Multivibrators or "One-Shot Multivibrators" as they are also called, are used to generate a single output pulse of a specified width, either "HIGH" or "LOW" when a suitable external trigger signal or pulse T is applied.

Another definition:

Monostable multivibrator, in which one of the states is stable, but the other state is unstable (transient). A trigger pulse causes the circuit to enter the unstable state. After entering the unstable state, the circuit will return to the stable state after a set time. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot.

To simplify it's a circuit that when it receives an input pulse will produce an output waveform whose ON time is based on a capacitor-resistor combination then it will switch off.

These can be built with logic gates, transistors, or specialized integrated circuits. I'll explore some basic theory I'll focus on the CD4047 astable/monostable multivibrator.

The CD4047 is easy to configure for either mode, is low power, and has a voltage range of 3-15 volts, but works best at 5 volts. The circuit is strait forward just as shown.

Fig. 2 CD4047 Monostable Mode Multivibrator Waveform.

Fig. 2 illustrates the output from the CD4027 in the monostable mode. The input is a square wave but the differentiator formed by a 22pF capacitor created a positive going 'spike" that triggers a HIGH output whose ON time depends on the values of C1 and R1. The formula is Q = 2.48 * R1 * C1. In the example above Qon = 2.48 * 0.0000001 * 90,000 = 22.34 mSec.

Changing C1 to 2200pF and R1 to 10,000, Qon = 2.48 * 0.0000000022 * 10,000 =~ 55uSec.

A monostable can be useful for signal conditioning or time delay circuits. My test using polarized capacitors shows polarity doesn't matter.

## Earth Science

Fighting to keep religion and politics out of science. Scientific method only!

10% of the earth's water is water vapor. Plants use water for photosynthesis which releases water into the atmosphere. Plants produce water vapor as does the oceans and surface water evaporation. More vegetation more water vapor more LOCAL climate variation, more water more plants, etc. The process is known as transpiration.

Water vapor can be as high as 4% of the atmosphere or 40,000 PPM. Formula = N% X 10,000

CO2 is 400 PPM depending on temperature. Warm water holds less CO2 than cold water. The atmosphere is 0.04% CO2.

Ratio of water vapor to CO2 is 100 to 1.

Guess what that means.

Ref. www.nasa.gov 11/17/2008 "Water vapor confirmed as major player in climate change"