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.
Dual power supply of 2.5V was used to power up the op-amp.
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.
\(f_c = \frac{1}{2 \pi R C}\)
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.
The following shows the frequency response of the active LPF.
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?
