LED sequencer circuits or ring counters are usually constructed by combining clock pulses with counter circuits. Generally, the input clock can be of any type, such as through discrete components, astable multivibrators, inverters, logic gates, or dedicated timer ICs (such as 555). The counter can also be of any type, such as 4-bit, 8-bit, decimal, or shift register. Depending on the charging time of the capacitor and the bias of the transistor, discrete components can also be put together to make an LED sequencer. Therefore, in this project, we will use the BC239 NPN transistor to build an LED sequencer circuit . BC239 is an amplifying transistor, the collector-emitter voltage is about 25V. This transistor provides a collector current of approximately 0.1A. In addition, the transistor provides an operating and storage junction temperature range of -55 °C to +150 °C.
Circuit diagram and work description:
The operation of this circuit is very simple. After completing the circuit, the 3V DC signal acts as a control signal on the base of the first transistor, and the first LED is turned on. Then the DC output of the collector of the first transistor is used as the control signal for the base of the second transistor, and the second LED is turned on after a fixed time delay due to the capacitor (22uF). Then the output of the second transistor enters the base of the third transistor, and the third LED turns on. The collector output of the third transistor loops back to the base of the first transistor as a control signal. Therefore, the LED sequencer continues to cycle until the circuit power is cut off.