Here second order active low pass filter design and test is illustrated. The active filter is build on a breadboard and the input and output signal amplitude waveform to and from the filter is tested. Also the frequency spectrum and frequency response graph is shown for the designed filter. This test can be performed easily at home requiring just PC/laptop and PC soundcard software.

**Recommended Prerequisites**

- Active 1st Order Low Pass Filter Design on Breadboard
- First order Active HPF Design and Test
- Active 2nd order HPF with LM358

### 2nd order Active LPF on breadboard

For the construction of the active low pass filter LM358 operational amplifier is used. Other operational amplifier like TL072 can be used as well. The following shows the active low pass filter on a breadboard.

### Circuit diagram

The following shows the circuit schematic diagram of the above constructed active high pass filter.

The active 2nd order low pass filter consist of two RC low pass filter at the input. The first LPF is formed by the resistor R1 and capacitor C1 and the second LPF is formed by the resistor R2 and capacitor C2. The resistor Rf and R3 provides the passband gain for the filter. For Butterworth response with flat passband, the passband gain must be 1.586.

### Calculation

The cutoff frequency for the filter is given by the mathematical expression below.

_{1}= R

_{2}= R and select the capacitor values C

_{1}= C

_{2}= C. Then the above formula for the cutoff frequency becomes,

_{1}= R

_{2}=15kohm and C

_{1}= C

_{2}= 0.01uF. This gives cutoff frequency of 1khz.

_{F}get is set by the resistors R

_{F}and R

_{3}which is given by the following equation.

_{F}= 1.586 so we can calculate the value of R

_{F}by setting R

_{3}.

_{3}=10kohm and with A

_{F}= 1.586 we get R

_{F}=5.86 KOhm.