Dancing Leds

Until now we had dealt with 2 projects in detail so now in this project we will be seeing how we can operate different LEDs with a single transistor.

Again this concept is totally based on bjt as switch.

Components required are:-

12v battery

12 to 15 leds

Mic

Transistor(bc547)

Resistors()

Capacitor(100uf)

Diagram Of The Project:-

Working of the project:-

We used fixed bias technique in this project. By biasing we set the base-emitter voltage to 0.7volts (Vbe=0.7v) and then we are giving an audio signal to the base of the transistor

So we should understand the working of the project in 2 cases

CASE-1:- When the Amplitude of the Audio-signal is High

When the amplitude of the Audio signal is high then the input becomes Vb = (0.7) + (audio-signal) and as we had studied in bjt as a switch that if Vbe is high that means Ib and Ic both would be high and if Ic is high that means voltage drop across collector-emitter terminal(Vce) is less,in-short our transistor acts as a closed switch or in other words we can say that our transistor operates in the saturation region. Therefore all the LEDs remain on in this case.

CASE-2:- When the Amplitude of the Audio-signal is Less

When the amplitude of the Audio signal is less then the input becomes Vb = (0.7) - (audio-signal) and as we had studied in bjt as a switch that if Vbe is less that means Ib and Ic both would be less and if Ic is less that means voltage drop across collector-emitter terminal(Vce) is high,in-short our transistor acts as an open switch, in other words, we can say that our transistor is operating in the cutoff region and due to which all the LEDs remain off in this case.

Here is the video through which your concept would be more clear

VIDEO:-