What is an LC Filter ?
An LC Filer is a circuit that removes frequencies from a power supply and smooths / cleans it so the equipment being powered gets a clean power source. In FPV sometimes we find our picture being effected by this dirty power supply.
There are many causes of the interference. If the interference is constant its normally rf based, ie your vtx or camera is providing the noise because its constant. If however the interference increases and decreases with the throttle this is down to the ESC. The speed ( frequency ) of the motor directly has an effect on the amount of interference seen.
ESC interference can sometimes be fixed by simply wrapping the servo lead from the ESC round a ferrite ring 5 or more times. In most cases that sorts it out. If not then its time for a LC filter.
What is one ?
An LC is one of the most basic filters going. It comprises of one or more coils and capacitors. What it does is remove frequencies from a voltage but high and low.
Are they new technology ?
Not at all, if you sat in your front room now chances are your looking at 2 or more. Your home speakers have them inside the speaker box, the filter in this case are used for the sound wave frequencies. They are in this case referred to as crossovers. The small speakers in your hifi cant cope well with bass, so an filter is used to remove the low frequencies ( bass ) so they only reproduce the high ones ( Treble. ) The same with the bass speakers, the higher frequencies are removed so it only produces the low bass frequencies. Where stereos crossovers let some selected frequencies through we use them to get rid of all of them.
They sound complicated
Not at all, with the most basic soldering skills and a near by maplins store your laughing.
There are a few different filters we could use for FPV. The first and most simple normally is all you would need. To make this all you need is :
1) Your power cable that's going from your lipo to your transmitter / camera
2) Ferrite ring
3) Capacitor
The capacitor value can be anything from 220 up to 2300 uf ( microfarads ) The lower the value the better for FPV use as apposed to general use, i use 1000uf ones. The capacitor is available through maplins
You want the VH52G ( 0.74p ) you could go for the VH50E but i recommend the higher voltage one so you can connect to any lipo cell pack without a worry.
A ferrite ring off ebay, get a pack of them, you can never have enough ferrite rings when Fpving :)
To make it it couldnt be simpler. Take your components :
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1010.jpg)
You need to wrap your wire around the ferrite ring. 5 times or more is fine, the red wire only needs to go round, but doing both has no ill effects so its up to you, using both will look like this :
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1012.jpg)
I choose to only use the red myself so mine looks like this :
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1011.jpg)
Next take your wire and strip both leads a little, this is to solder the capacitor too. depending on how you want the capacitor to sit depends on how far away from the wrapped ferrite ring you strip at.
The picture below shows heat shrink I`ve put on the wires either side of the ring, i did this to keep the red wire tight on the ring and for neatness only :
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1013.jpg)
The capacitor we are using has to have the correct wire ( either positive or negative ) going to the correct side. The capacitor a thick stripe down one side of the metal can. In the thick stripe are marking like - - - - in it. This indicates the negative side of the capacitor so the negative wires go the the leg of the capacitor the stripe is one.
Here is an example of the stripe :
(http://i108.photobucket.com/albums/n39/cayote64/cayote64002/cap_zpsxe0mphjy.png)
Make sure this is correct or the capacitor will blow up when you power up.
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1014.jpg)
Once you have soldered the capacitor legs to the power wires you then need to insulate them so they cant short out, a bit of heat-shrink does the job fine :
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1015.jpg)
There you go, one LC filter made, no all you need to do is solder / connect the lipo balance lead to one end and the other to the vtx / camera power leads.
(http://i108.photobucket.com/albums/n39/cayote64/DSCF1016.jpg)
The correct way round to have the filter is with the coil end to the supply ( lipo ) the capacitor end to the vtx / camera
That's it, power it up and enjoy interference free flying :)
There are a few variations on this circuit. Lets say you have a very long lead to your vtx, for instance you have to have the vtx on the tail of the plane, in that case the only extra you really need is to add a diode before the circuit on the +ve wire, a diode like this :
http://www.maplin.co.uk/module.aspx?moduleno=46385 (http://www.maplin.co.uk/module.aspx?moduleno=46385)
That removes half the noise before it even gets to the rest of the circuit.
Simply cut the red wire before the coil and solder the diode in between with the end marked with the bar on the diode towards the coil. Again heat shrink over it to insulate.Which way round the capacitor is in this circuit ie before or after the ring doesnt really matter.
Thats it, power it up and enjoy interference free flying :)
If you want ill put up circuit diagrams for all of them, there is another circuit that uses another two capacitors, a 47uf and 100uf with the diode as well, its slightly better than the basic if you need even more filtering :)
Neater than mine Ian - nice job.
nice overview and build Ian... very useful.
Just one thing... it looks like you've wired my filter into your gear for the demo... would have been easier just sending it over :D
Lol cheers Martin, Steve im doing yours with a 470uf capacitor, its the other end of the value range.
Then if you can can you report back any difference in the filter, there probably wont be any at all but if its even better then it would be handy to know :)
Wow what can i say very useful and informative very detailed and good lay out ian cheers
Even closer to home than the crossovers in your speakers, you'll find lots of LC (tuned) circuits in both transmitters and receivers either filtering out unwanted frequencies or resonating at desired frequencies.
A lot of guys already fit ferrite rings to servo leads in order to dampen rf pickup.
Good thread coyote. :)
Thanks, yes they are everywhere ! Normally just a ferrite will work on its own especially for rf interference only but other times you need a little more help :)
Excellent thread, thanks.
Got some caps in from maplins, gonna head down the workshop in a min and make me one of these puppies...
You can see my current interference when I fire up the motor on my recent Beevo video (see my beevo thread), lets see if this sorts it out!
Quote from: Coyote on December 13, 2010, 07:11:51 PM
The capacitor has marking on its housing, the side with - - - - on it is to go to the I`ve lead.
I'm presuming you mean live lead? :)
Quote from: Coyote on December 13, 2010, 07:11:51 PM
What is an LC Filter ?
Which way round the capacitor is in this circuit ie before or after the ring doesn't really matter.
Ian,
Great article - BUT, I'd say that it DOES matter where the cap is for this simple filter.
The inductor should be nearest the input (battery/supply) and then the capacitor nearest the output.
There is a good explanation on RCG (and a long argument) regarding ideal components and placement in LC circuits...
Nigel.
Quote from: Pasty on December 16, 2010, 10:27:58 AM
Quote from: Coyote on December 13, 2010, 07:11:51 PM
The capacitor has marking on its housing, the side with - - - - on it is to go to the I`ve lead.
I'm presuming you mean live lead? :)
Nope. Both leads are live, one is +ve and the other is -ve. The dashes (- - - -) mean -ve side. Electrolytic capacitors are polarised and I have seen some marked with the +ve side.
Quote from: Pasty on December 16, 2010, 10:27:58 AM
Quote from: Coyote on December 13, 2010, 07:11:51 PM
The capacitor has marking on its housing, the side with - - - - on it is to go to the I`ve lead.
I'm presuming you mean live lead? :)
never assume :D
Wired it up and the cap went pop.... and thinking about the markings on the side of the cap, "- - - -" surely means negative? Lucky I bought more than one :D
When I got the pop/smoke/stink/weird liquid I feared the worst (as a leccy noob would) but only the cap went pop.
lets try this again...
Hi Pasty, looks like you found out the hard way. You must have wired up and watched the smoke before I posted my answer.
Better luck next time.
BTW be careful how you wind the wire round the ferrite ring. Do it in the wrong direction and you will cause a catastrophic shift in the Earth' axis resulting in the destruction of all living things. Naw. just kidding.
;D
Even manufacturers sometime make boobs. I bought a transmitter once (an expensive upmarket one) and opened up the back to discover that some of the top panel switches had not been soldered onto the circuit boards. I finished the job myself with the manufacturers approval to avoid delay and postage costs. Mecifully no pop/smoke/smell ensued when I switched on.
ehehe... thanks for the reply... but I move fast :)
I wouldnt have known what +/-ve means anyways! best to keep leccy terms as basic as poss for us no leccy chaps... thats simply positive and negative yeah?
Quote from: Pasty on December 16, 2010, 12:03:59 PM
ehehe... thanks for the reply... but I move fast :)
I wouldnt have known what +/-ve means anyways! best to keep leccy terms as basic as poss for us no leccy chaps... thats simply positive and negative yeah?
Yes +ve means positive and -ve means negative. However if you are going to get into making up small items for yourself you must make yourself aware of the industry conventions. You've learned that today and will be unlikely to forget it.
Moving on from this, sometimes -ve is called common. For example with a servo lead which has three wires. One is +ve, one is signal and one is -ve. The reason for this is that the +ve and signal wire need a "return" wire to complete their curcuits. They share this by both using the -ve or common as it is called. It would not be called the common when you have only two wires as in the case of the battery lead you are making up the filter for.
There you go, it's long been known that electronic circuits really run on smoke and all works fine, unless you make a mistake and let the smoke out, then the circuit doesn't work any more.
Worse still, you cannot put the smoke back in.
Nigel.
Quote from: Devonian on December 16, 2010, 11:01:19 AM
Ian,
Great article - BUT, I'd say that it DOES matter where the cap is for this simple filter.
The inductor should be nearest the input (battery/supply) and then the capacitor nearest the output.
There is a good explanation on RCG (and a long argument) regarding ideal components and placement in LC circuits...
Nigel.
Thats right there is an argument for both, so far from what ive seen theres no difinitive answer so far, thats why i sat on the fence lol :)
I know which way I make my LC choke input filters ;)
There is sound reasoning to have the inductor first in a single inductor, single capacitor LC circuit
http://www.tpub.com/neets/book7/27f.htm (http://www.tpub.com/neets/book7/27f.htm)
Nigel.
Thats a case, ok then lets say it would be better coil first then ill ammend :)
I find that out now AFTER I've wired it in the other way around :D
ok, a plea to all leccy bods, if you're going to use indutry standard speak for guys who arent and never will be in the industry please explain wtf you're on about when using abbreviations and terms non leccy people wont understand :D
Hee hee :) Well you can do it both ways Steve, but to have the inductor ( coil ) first does make sense :)
Another good post (and reasoning why it's inductor nearest the input voltage)...
http://www.rcgroups.com/forums/showthread.php?t=1055252 (http://www.rcgroups.com/forums/showthread.php?t=1055252)
Both Sander and Thomas Scherrer know how it should be done.
No need for a diode in this circuit, as it would also drop the output voltage by ~0.6 volts as well ;)
Pasty,
Sorry, but 'twas a 50/50 chance weren't it ?!
Nigel.
hey ho Nigel... its all part of the journey :)
I'm pleased to report my LC filter (with WAY over sized capacitor :-[) is working a treat, from what I can tell its removed all the interference I had previously.
Thanks to Ian for sharing the knowledge and thanks to the rest of you for the bits of help and sympathy :D
Quote from: Pasty on December 16, 2010, 04:40:43 PM
I find that out now AFTER I've wired it in the other way around :D
ok, a plea to all leccy bods, if you're going to use indutry standard speak for guys who arent and never will be in the industry please explain wtf you're on about when using abbreviations and terms non leccy people wont understand :D
To be fair to Coyote +ve & -ve are in common use and not really confined to the electrical/electronics industry. Surely you have seen + & - on battery terminals.
BTW you might be interested to know the following :
L means inductor, in this case the ferrite ring
C means capacitor
Inductors allow passage of low frequency signals but supress high frequency signals.
Capacitors allow passage of high frequency signals but supress low frequency signal.
That is how audio crossover networks, referred to earlier by Coyote, work. Combinations of these components are also used to create resonant circuits which is where my earlier reference to transmitters and receivers comes in as well as filtering circuits in our r/c gear.
Super mate, amazing how something that electronically simple can be so effective :) Not you the filter ;) :)
Following Ian's excellent LC filter build up - i made a few of my own.
They work really well.
(http://s1.postimage.org/26yu8rev8/DSC00001.jpg) (http://postimage.org/image/26yu8rev8/)
Old PC motherboards contain all the parts you need.
(http://s1.postimage.org/26yvward0/DSC00002.jpg) (http://postimage.org/image/26yvward0/)
Removed the torroids & high value capacitors.
(http://s1.postimage.org/26yxju3us/DSC00003.jpg) (http://postimage.org/image/26yxju3us/)
I have a few now...
(http://s1.postimage.org/26yz7dgck/DSC00004.jpg) (http://postimage.org/image/26yz7dgck/)
I cut away the old copper wire & wrap my cable around as many times as i can.
(http://s1.postimage.org/26z0uwsuc/DSC00005.jpg) (http://postimage.org/image/26z0uwsuc/)
Solder the capacitor onto the cable (black to negative) - done!
(http://s1.postimage.org/26z2ig5c4/DSC00006.jpg) (http://postimage.org/image/26z2ig5c4/)
Here's one i made - heatshrunk & tidy.
Neat job Badlands. :)
When I was an impoverished schoolboy (60s/70s) we used to strip components off any circuit boards we could lay our hands on. Nowadays there just isn't as much you can remove what with multi pinned or surface mounted devices. However there appear to be more ferrite rings and crystals these days, not to mention any amount or surplus computer equipment. My company IT dept is always chucking out perfectly good but slightly old gear. I rescued the 19" flat screen monitor I am now using quite literally from the bin along with another that only had cosmetic damage. Power supplies seem to be popular for home charging of flight packs and some people have even converted the brushess motors from CD/DVD drives to power models. Mind you brushless is pretty cheap now so hardly worth the hassle.
I agree.
Ive rescued many old laptop mains adapters from the scap @ work, some are 12v @ 6amps, they are perfect for powering 12v lipo charges. Most of the time the cables have failed thru wear & tear - an ez fix for a nice PSU.
:-)
Cool Martin looks spot on bud ! :)
Never thought of recycling :)
I like the recycle idea... off to the loft for me! :)
Have you tried them yet?
Yes - fitted one to my GPS unit (torroid only).
Works really well, sometimes i was waiting 20 mins to get a GPS lock - now from cold i have GPS lock in 90 seconds.
(http://s2.postimage.org/lejxb2p0/gps.jpg) (http://postimage.org/image/lejxb2p0/)
Ive added one to my Steathwing & will report back the results once its finished.
thanks for that coyote i made one and it has improved my video,i will fit one on all now
Most welcome, they are really effective arnt they :)
Running the whole system from one lipo is in my oppinion better than two. Once its filtered if needed its fine.
I got lost a bit with the rest, do you have diagrams of the more complex filters ? If so then yes please do post them up :)
Which diagram do you want me to post, the one for your system ?
(http://i108.photobucket.com/albums/n39/cayote64/lc.png)
Hi all, ive deceided to put an LC filter in my easystar set up that uses an ezosd.
I will put the ferrite ring in then the capacitor on the power / video in lead. Is there any point adding a ferrite ring on the video out lead to the camera?
Thanks
Ant
Quote from: Coyote on April 01, 2011, 10:20:15 PM
(http://i108.photobucket.com/albums/n39/cayote64/lc.png)
Hi,
better will be to use 10-47 nF in place of last 100 uF. Diode - any Schottky type switching diode.
Other idea - in place of ferrite ring - put 10 uH axial inductor with size proper to you current.
Using LC-filters = 10 uH axial inductors + 10-47 nF capacacitors, are very good and cheap solution for protecting all servo signal lines (specially when you use extending cables).
Marek
These filters are good
http://www.flytron.com/70-mickey-1-amper-power-noise-filter.html (http://www.flytron.com/70-mickey-1-amper-power-noise-filter.html)
Power everything bar escs through one of these. So, basically take power off for all your onboard FPV kit/ BEC after the current sensor through the filter. As with all current sensors do NOT use the GND and + wires, just the current sense output. ;D (big discussion on this by Ren on RC Groups)
my my lc filter done today following ian (coyote) mod..cheers ian
(http://s3.postimage.org/819n83us/IMAG0340.jpg) (http://postimage.org/image/819n83us/)
Here mine for long range Skywalker with 4s 10000mah, tapping 3s power for VTX and Camera.
(http://img508.imageshack.us/img508/183/20110915172125.th.jpg) (http://img508.imageshack.us/i/20110915172125.jpg/)
(http://img580.imageshack.us/img580/1419/20110915172306.th.jpg) (http://img580.imageshack.us/i/20110915172306.jpg/)
Nice work lads, have you noticed any difference ?
Will let you know when tested. ;)
Yeah me too..not had chance to test yet ''but soon.
Ok tested LC filter and 99% of interference is gone. :)
..you never get any interference in your vid feed -- :)
Sorted Chris....... Result !
So 3s 1000mah (90g) is removed and now power vtx/camera from 12v feed from 4s balance plug(s), i always balance charge so not a problem. :D
Will use same system in Skywalker when carrying 4s 10000mah.
Great guide, thanks a lot!
If you're in any doubt if these work or not here's the proof
http://youtu.be/tYq90M33KrI (http://youtu.be/tYq90M33KrI)
Theses look shit hot
http://store.ivc.no/product/lpf-01 (http://store.ivc.no/product/lpf-01)
Thank pksurfing for the link
If you buy one let me know, would be good to see how well they work
Quote from: bignose13 on June 03, 2014, 09:08:10 PM
If you buy one let me know, would be good to see how well they work
I have one, use it in my big wing with RVOSD and video is crystal clear.
That being said, it also does funky things to some devices. On my Disco Pro, putting that filter in front of my VTX totally borked the tbs core for some reason. Their site even says something about it:
QuoteUpdate March 2013: It is now possible to select between common mode and differential mode filtering. A solder jumper pad on the input side disables filtering on the negative/ground-lead. If you experience issue with OSD systems, try changing the filter to differential mode.
And despite trying the jumper pad, it still didn't work, so I removed it and my TBS Core started working again. No idea how or why but there you go.
Ian did i do a boo boo?
powered up and smoke and pop.
ok is the one with like - > - > - > plus or minus? i put it as plus?
(http://i152.photobucket.com/albums/s195/PrInCeUKER/RC/DSC_8798_zps917a274c.jpg) (http://s152.photobucket.com/user/PrInCeUKER/media/RC/DSC_8798_zps917a274c.jpg.html)
Your capacitor is on the wrong way around Darren, the side with the - > band on it is 0v
will make another in abit :(
cheers Ian :)
electrolytic capacitors really don't like reverse voltages.
Quote from: quadbod on August 06, 2014, 09:01:56 PM
electrolytic capacitors really don't like reverse voltages.
Nope did not like it a bit. it spat at me made my arse go :)
These little Murata filters are great (good to 10A, the 023 is able to handle even more - 15A iirc):
http://www.ebay.co.uk/itm/MPN-BNX022-01L-Filter-Emi-Dc-Line-MURATA-Pack-of-1-/251407021561?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3a8906b5f9 (http://www.ebay.co.uk/itm/MPN-BNX022-01L-Filter-Emi-Dc-Line-MURATA-Pack-of-1-/251407021561?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3a8906b5f9)
Sometimes you can find them assembled onto PCBs with easy to solder terminals
I have the little eachine et200 tx and camera, the the camera is powered by the tx. Should I put the capacitor before the tx, or after it (before the the camera) ?
Before the transmitter so the transmitter has clean power and the passes it on to the camera.
Cheers mate!
Please can someone help me get rid of motor interference on my Skysurfer.
I have the Eachine 600mw vtx out near the wing tip and have a standard (long) flat servo lead feeding it with +&-. The white wire is bringing the video via one of 3 camera's chosen from my HK 3-way switcher . The "video out" white wire then leaves the switcher , goes through my G-OSD3 osd and then out to the vtx.
I've just tried fitting an LC filter to the power supplied from one of the flight batteries balance leads which only powers the osd and vtx. It made no difference?
SO- I then tried the filter on the other flight batteries balance lead which powers a Ubec which then powers the three camera's - no difference??
SO- I then fitted it in the lead from the ESC to the rc rx -you guessed it - no difference?
SO- I then tried it on the wing on the +&- supply to the vtx - "bugger all" difference??
Please :-* anymore suggestions ;D
You should be filtering your VTX, Camera and OSD. So if they are all powered separately, you need 3 LC filters.
And the filters need to go after any switching regulators. eg. Battery->UBEC->FILTER->Camera
Quote from: dogzilla on September 25, 2015, 11:54:11 PM
You should be filtering your VTX, Camera and OSD. So if they are all powered separately, you need 3 LC filters.
And the filters need to go after any switching regulators. eg. Battery->UBEC->FILTER->Camera
Thanks for coming back!
So since I need to filter each of the 3 cams plus the vtx, and osd , so should I use 5 filters then?
Could I try ferrite rings first -the lc filter was £6 so five would be pretty expensive :o
I beg to differ. You shouldnt need LC filters at all
It would be interesting to see a circuit diagram showing what is connected to what and a photo or 2 of the reality.
Using servo cable on long runs is not great. It is better to use cctv cable. Also dont have any signal wires going anywhere alone. They should always be paired with a ground return wire. (Current goes one way along signal and the same current returns via ground so cancelling magnetic effects)
You should look at your camera switcher as a "hub" and have power going in there from batt and out to your camera and Vtx as end nodes. If camera switcher cant supply cam/vtx voltage then stick a Switching PSU ( 12v BEC) right by it so you can follow the above ground return rule.
Usually junk on video is cause as ground going to camera is carrying current for other devices, violating ground return rule.
regards
Andy