This project is a simple 4-stage transistor timer built entirely with discrete components.
The circuit is made from four monostable multivibrator stages connected together. Each stage produces a timed pulse before triggering the next stage. The result is a sequence of four timed events, indicated by four pairs of LEDs.
How does it work ?
A monostable multivibrator has two stable states, but when it is triggered, it temporarily switches to its other state and then automatically returns to its original state after a certain amount of time.
In this project, four monostable stages are connected in sequence:
Stage 1 → Stage 2 → Stage 3 → Stage 4
When the circuit is powered on and triggered, the first stage starts its timing period. Its output then triggers the second stage, which starts its own timing period. The process continues until the fourth stage has completed its cycle.
Each stage uses a pair of transistors, resistors and capacitors to create the required timing effect. LEDs provide a simple visual indication of the different states of the circuit.
The duration of each stage can be changed by modifying the components that determine its time constant. In particular, changing the timing resistor or capacitor allows the delay to be increased or decreased.
Electronics component Fun Kit (with breadboard & power supply module)
General purpose transistors - BC547 (NPN) & BC557 (PNP) pack
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