Active 1st Order Filter Design on Breadboard

 Here an active first order filter design is build on a breadboard and tested. The operational amplifier used here is LM358. The filter is tested with signal with different frequencies. Also shown is the frequency response of the designed filter.

Active LPF on Breadboard

The low pass filter build on a breadboard is shown below. The LM358 op-amp is used as the active component of the filter.

first order active low pass filter with LM358 on breadboard

Dual power supply of 2.5V was used to power up the op-amp.

1st order LPF active filter with LM358 on breadboard

 How the split power supply was obtained can be seen in the wiring diagram below.

Schematic Diagram

The schematic diagram of the active LPF circuit is shown below.

first order LM358 LPF active filter circuit diagram
 The cutoff frequency for this LPF is 1KHz. This cutoff frequency is set by the capacitor C and the resistor R. The cutoff frequency is given by the formula,

\(f_c = \frac{1}{2 \pi R C}\)

Given the frequency fc=1KHz and by choosing capacitor of 0.01uF we get resistor value of R=15.92Kohm. Here we have used 16Kohm resistor by series connection of 15KOhm and 1KOhm resistors.

A passband gain of 4 was selected. This passband gain Af is set by the resistors Rf and R1 and is given by the following formula.

\(A_F = 1 + \frac{R_f}{R_1}\)

With Rf=1kOhm and Af=4 we get R1=333.33Ohm but we used practical value of R1=330Ohm.

All the above component values was calculated using the First Order Active Low Pass Filter Calculator Online.

Testing and Results

The filter was tested with signal with different frequencies. From low frequency of below 200Hz(below than this is not required) to 10KHz frequency was tested.  As the frequency increased from 900Hz or so the output signal amplitude decreases upto and above 10KHz. This is as expected from a low pass filter. This is shown in the video. The video also shows the frequency response of the active filter.

The following shows the input and output signal waveform into and out of the first order active filter.

signal waveform of input output from first order active LPF

The following shows the frequency response of the active LPF.

Frequency response of first order LPF with LM358

Further recommendation

See the following tutorials:

 - Second Order LC Low Pass Filter Calculator

How to design Multiple-feedback band-pass filter?

- How to design Twin T Active Notch Filter? 

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