A monostable multivibrator is a type of multivibrator that is only stable in one state. It will stay in the stable state until there is an input to switch it to the other state. A short time after the input is removed it will return to the stable state.

In this version of the monostable multivibrator, the schematic for which is shown here, two LEDs, one red and one green, are included to show which state the circuit is in. The push switch is used to switch the state of the monostable. When the switch is pushed the circuit will change to the unstable state. A short time after the switch is released the circuit will change back to the stable state.

This circuit can be run from a six volt battery supply, such as four AA cells, or from a six volt DC power supply. The actual voltage is not critical, it should work from four volts upwards, but it is recommended not to go higher than nine volts.

The circuit is laid out on the breadboard in a similar way to how it is drawn in the schematic.

The switch was not easy to press into the breadboard, the legs had to be twisted to line up with the breadboard contacts, and it could be connected via flying leads if it proves to much of a struggle to get it to fit.

When the circuit is first powered the green LED will light and the red LED will be extinguished. When the switch is pressed the green light will extinguish and the red LED will light. A short time after the switch is released, about one second with the values used, the red LED will extinguish and the green LED will light once more.

Here the is circuit laid out and working on an actual breadboard.

This is just a small section of a much larger breadboard. The extra components are capacitors that I usually have scattered across the breadboard to eliminate noise from the power rails. They make no difference to this circuit.

The extra links are because this particular breadboard has a break in the horizontal rails at the mid point. I don't want this break so I usually keep these positions jumpered.