Good day, dear readers! Today we will talk about assembling a simple low-pass filter. But despite its simplicity, the quality of the filter is not inferior to store-bought analogues. So let's get started!
Main characteristics of the filter
- Cutoff frequency 300 Hz, higher frequencies are cut off;
- Supply voltage 9-30 Volts;
- The filter consumes 7 mA.
Scheme
The filter circuit is shown in the following figure:
Parts List:
- DD1 - BA4558;
- VD1 - D814B;
- C1, C2 - 10 µF;
- C3 - 0.033 µF;
- C4 - 220 nf;
- C5 - 100 nf;
- C6 - 100 µF;
- C7 - 10 µF;
- C8 - 100 nf;
- R1, R2 - 15 kOhm;
- R3, R4 - 100 kOhm;
- R5 - 47 kOhm;
- R6, R7 - 10 kOhm;
- R8 - 1 kOhm;
- R9 - 100 kOhm - variable;
- R10 - 100 kOhm;
- R11 - 2 kOhm.
Making a Low Pass Filter
A voltage stabilization unit is assembled using resistor R11, capacitor C6 and zener diode VD1.
If the supply voltage is less than 15 Volts, then R11 should be excluded.
The input signal adder is assembled on components R1, R2, C1, C2.
It can be excluded if a mono signal is supplied to the input.In this case, the signal source should be connected directly to the second pin of the microcircuit.
DD1.1 amplifies the input signal, and DD1.2 directly assembles the filter itself.
Capacitor C7 filters the output signal, a sound control is implemented on R9, R10, C8, it can also be excluded and the signal can be removed from the negative leg of C7.
We've figured out the circuit, now let's move on to making the printed circuit board. For this we need fiberglass laminate measuring 2x4 cm.
Low Pass Filter Board File:
plata.zip
[25.04 Kb] (downloads: 943)
Sand the surface to a shine with fine-grained sandpaper and degrease the surface with alcohol. We print this drawing and transfer it to the textolite using the LUT method.
If necessary, paint the paths with varnish.
Now you should prepare a solution for etching: dissolve 1 part of citric acid in three parts of hydrogen peroxide (proportion 1:3, respectively). Add a pinch of salt to the solution; it is a catalyst and is not involved in the etching process.
We immerse the board in the prepared solution. We are waiting for the excess copper to dissolve from its surface. At the end of the etching process, we take out our board, rinse it with running water and remove the toner with acetone.
Solder the components using this photo as a guide:
In the first version of the drawing, I did not make a hole for R4, so I soldered it from below; this defect is eliminated in the download document.
On the back side of the board you need to solder a jumper:
The assembled circuit worked the first time it was turned on and does not need any configuration. If there is no sound at the output, twist the variable resistor and check all connections on the board.
This concludes my article. Good luck with your repetition everyone!
A few photos of the finished product:
