The monostable flip flop is a electronic circuits that is used to produce a single pulse each time it is triggered. Sometimes, this circuit called a ‘one shoot’. This circuit is very useful, for example it can used to produce a delay for timing applications or debounce a mechanical switch so that only one rising and one falling edge occurs for each switch closure. Here is the circuit :

Non Retrigerable Monostable Multivibrator circuit schematic

The left transistor normally conducts while the right side is turned off, when it In the discrete circuit. The conducting transistor will turn off when the switch grounds the base of it is pressed, so the collector voltage will rise. The capacitor begins to charge through the base of the opposite transistor because of the rising of the collector voltage. So it will switch on and produce a low state at the output. To keep the output stage saturated, the low output state holds the left transistor off until the capacitor current falls below. When the output side begins to turn off, the left transistor  returns to it’s conducting state because of the rising voltage. It has a lowers voltage at it’s collector. So the capacitor to discharge through the 10K resistor (emitter to base).  The circuit then remains in a stable state until the next input.

Note : These circuits are not re-triggerable and the output duration will be shorter than normal if the circuit is triggered before the timing capacitors have discharged which requires about the same amount of time as the output.