How to Build BJT amplifier and test with Soundcard based PC Oscilloscope

 Here a BJT amplifier using 2N3904 transistor is designed and tested. The voltage divider biasing method is used for the design of BJT amplifier. The BJT amplifier is constructed on breadboard and a free sound-card based oscilloscope is used to analyze the input and amplified signal.


 The design of BJT amplifier using voltage divider method was explained and the value of the resistor and capacitor were also calculated using online BJT amplifier design calculator. The following is the circuit diagram show the BJT amplifier with practical available resistor and capacitor value.

 To test the above BJT amplifier designed circuit, we will use the 2N3904 general purpose transistor. The amplifier is build on a breadboard which is shown below.

2n3904 BJT amplifier on breadboard

In the above picture a 5V DC supply was used.

Next we need to supply signal into the amplifier. For this we will use the soundcard oscilloscope software which you can download from the link below.

This software can both acquire signal through the line in/microphone input and display the signal on the PC but can also send out signals(sine wave, square wave, triangle etc) via the loudspeaker output port on the PC.

Here we will send sine wave of amplitude of 10mV and 1KHz frequency into the BJT amplifier build above. To do this we need to setup signal in the signal generator tab as shown below.

signal generator PC oscilloscope

This will output signal from the loadspeaker output of the PC. This is then fed into the BJT amplifier. The output from the amplifier circuit is then fed into the line in/mic input of the PC. This is shown in the figure below.

BJT amplifier using PC oscilloscope

In the above figure the white male to male speaker jack wire is used to input signal into the BJT amplifier on the breadboard. The output of the amplifier goes into the pref-board constructed voltage limiter and diode protection circuit. The output from this goes into the male to male green jack wire which is connected to the line in/microphone input of the PC. The signal path is shown below.

input and output to BJT amplifier using PC oscilloscope

See the following video demonstration:

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