Getting Started for Beginners - Simple Flash Circuit

Simple flash circuit

• working principle:

                          1. When the power is turned on, the two transistors will compete to turn on first, but due to differences in components, only one tube will turn on first. If Q1 is turned on first, then the collector voltage of Q1 drops, LED1 is lit, and the left end of capacitor C2 is close to zero voltage. Since the voltage across the capacitor cannot change suddenly, the base of Q2 is also pulled to approximately zero voltage, causing Q2 to cut off. LED2 does not light up.

                          2. As the power supply charges C2 through resistor R3, the base voltage of transistor Q2 gradually increases. When it exceeds 0.6 volts, Q2 changes from the off state to the on state, the collector voltage drops, and LED2 is lit.

                          3. At the same time, the drop in the collector voltage of transistor Q2 causes the base voltage of transistor Q1 to also drop through the action of capacitor C2. Q1 changes from conduction to cutoff, and LED1 goes out. In this cycle, the two transistors in the circuit will turn on and off in turn, and the two light-emitting diodes will continuously emit light in a cycle. Changing the capacity of the capacitor can change the speed of the LED cycle.

       ! ! ! After building the board, you need to put two 1.5V (AA batteries) into the battery box. Use wires to connect the battery box (BT1) and the circuit board. Pay attention to the positive and negative poles.