MattMade
DIY Maker Blog by Matt Morawiec
Jul 14 2016

LC Power Filter DIY

Home Brew Power Filter for Clean Current!

•Intro

In electronics, and especially in FPV multi-rotors, clean power is a must! Without a power filter you will get small black lines across your 5.8ghz video because of unclean power going into your camera and video transmitter! This will smooth out any voltage spikes and make your video crystal clear!

Get the Parts

  • Computer w/ Eagle CAD: Hope you have one!
  • Soldering Iron (+ solder): The most used and most important tool.
  • Capacitor of Choice: This depends on operating voltage and size of vehicle. If those go up, your capacitor gets bigger!
  • Inductor of choice: This depends on operating voltage and the size of the vehicle too!
  • Misc Materials: Solder flux, wire, pliers or side cutters

The Idea

I saw some of these online for some serious dough! So I thought I would be able to do it for cheap! These are basic circuits based on capacitors, which basically resist changes in voltage, and inductors, which basically resist changes in current. Put these together and you have a device capable of smoothing out voltage spikes and otherwise unstable input voltages as seen in multirotors!

The idea is pretty simple. Simply run your current in series with an inductor to protect from surges, and in parallel with a capacitor to remove any voltage spikes. The first thing to do was draw simple schematic:

Schematic

Prototyping

Now I wanted to make sure my design would work in the real world. I used some perf-board I had laying around, in conjunction with a DIY inductor made from a torroid coiled with copper wire and a 1000 micro-henry capacitor to bring my schematic to life.

Schematic

After some brief testing inline with my video equipment, I was happy with the results and ready to develop a finished product.

Choosing the Parts

The hacked parts I used in the prototype obviously wont work on a larger scale. Time to visit digikey, the best source for electronic components!

There, I started searching for inductors and capacitors that would fit the bill. The current handling capability had to be sufficient to run a video transmitter and camera, so 500ma was a minimum. If I planned to use 4 cell li-po batteries, the capacitor would have to be rated for 25 volts minimum if it would be able to hands voltage spikes up from a 16 volt baseline.

After some brief searching, I found these:

Capacitor

Inductor

Using these parts would let me draw up to 1000ma (one amp) of power and use 4 cell batteries. Perfect!

Designing the Printed Circuit Board

I planned to take advantage of low cost PCB prototyping available from OSH park, who I have used before. So I used Eagle CAD to design a low profile circuit board that would connect my components in the desired way. This is what I came up with:

PDB Front

PDB Back

Then I ordered 3 copies of the board along with 3 sets of components from digikey and waited!

Assembly

When I received all the parts, it was time to put it all together! The capacitor is through hole so its nice and easy! It is polarized though, so make sure to put it in the right way!

The surface mount inductor is a little more tricky. I tinned the pad and the inductor first, then placed it down firmly and reflowed the solder.

The finished product was very professional looking and works even better!

Finished

All 3!

Just solder it in series with your video gear or whatever to enjoy smooth power!