Electronics for RC Planes (integration, PWM and RSSI)

More on the $1.29 diversity controller for FPV RC planes and multirotors...
What is PWM and how does a capacitor turn a digital signal into an analog one?
In this video I look at "integration", a fancy term for simply using a capacitor to smooth out a noisy or digital signal.
The first example is the integration created by adding extra capacitors to the $1.29 diversity controller, the second example talks about turning a PWM RSSI signal into an analog one.
Let me know if you want more of this type of techy videos while I'm waiting for my flight exemption to come through.

[@stephenmoseley2350]

I was very lucky to have stumbled across Bruce as soon as i got into RC (was only a year ago) but I have learned so much from him. He has guided me through a minefield of technology via his videos and I am so grateful. If it wasn't for people like him then I'm sure a lot of people in a similar position to me would have had a real hard time with this hobby and may have given it up by now. I am currently doing an electrical engineering degree and the teachers are not a patch on this guy. If only there where more like him. Cheers Bruce, keep it up.

[@TotallyGlitch]

you may not do electronics introductions videos, but you sure one hell of a job making some of the most understandable electronics videos I have ever seen. Thank you very much Bruce.

[@airmyngarage]

Exellent Bruce. Simple straightforward explenation. You would make an awsome teacher.

[@DenysSene]

these series explaining some eletronics are great.

[@66tbird1]

Great lesson! The balloon analogy was a lot simpler that the way I was taught decades ago.

[@ThePwnageHobo]

Great video, Bruce. I've studied electrical and mechatronic engineering, and this the first time I've heard the capacitor balloon analogy. It's a great way to explain it. It'd also be useful to help people understand voltage ratings. Voltage rating is equivalent to air capacity. The more you fill it, the longer it takes to drain. Overfill it, and it pops.

[@rickstd7083]

Thank you Bruce for the time and energy you give to the community. ;)

[@bobclarie]

Well done Bruce, thanks for helping us understand the RC electronics. I shall call you the "Carl Sagan" of RC technology. Keep up the efforts; much appreciated by all. '73

[@columbiau2]

Absolutely fantastic. As an ex Navy ET and a Ham. I really enjoy the refresher training. An how this all relates to the RC hobby. Keep up the good work.

[@rpgeezus]

Bruce, please make more of these videos. They're fantastic!!

[@Varpanr1]

I love this! I absolutely want to see more videos from you explaining the tech we're using in our hobbies

[@agentbertram4769]

I am an retired electrical and BMS controls engineer Bruce, but I am hugely ignorant regarding the stuff used in RC radio control. Your tutorials are blooming marvellous for an old timer or a newcomer alike, to get up to speed in this most interesting field. Well done mate - as we say in Scotland "Lang may yer lum reek" Translated this Scottish saying becomes "Long may your chimney smoke" - meaning 'May you live long and keep well'. Perhaps Mr Spock of Star Trek fame said it even better "Live long and prosper". Frankly when it comes to your videos I haven't enjoyed anything so much in a long, long time. Even the pedantic ranty ones. :O)

[@spleefdowny]

Love these techie vids, Bruce -- keep it up! Every time you put one of these out it makes me want to learn more!

[@aeroscience9834]

Yes, you should do more of this type of videos.

[@iam12hak]

Keep these up. They are excellent! simple application of electronics with a direct purpose in rc and are very helpful :)

[@brucebfd]

That reminds me of the switching BEC video that you did before thanks for the tech Information... It really helps And it makes it more fun... Thank you

[@sokolum]

Bruce... Thank you again, again, again for your great video and your time of investing to make them! Inspirational.

[@KennethElstonBAK]

Hungry minds wants MORE!!!!! Very good, thanks for the vid.

[@LikeOnATree]

Awesome video, very informative! Thanks for taking the time to make it!

[@nigelholland1811]

Most of that went over my head but I see the principle. You just make it sound interesting.

[@TraxxasRustler27]

Hey this video helped out on my linear circuits 1 lab quiz the other day. Thanks a lot! Great videos. Keep it up Bruce!

[@godsgifttocockpit]

Thanks again for a great video. I don't think you could explain the workings of an capacitor in this concept better than with the balloon analogy. I only wish my electronics professor had done this wayyyy back in time :)

[@patrickploenzke489]

Thank you very much Bruce. Very useful for all us Taranis users.

[@Flyswamper]

Bruce, Nicely done sir! You do a great job with the explanations here! It's videos like this and people like you that enable people like me to go from treating so many of these things as "mysterious black boxes of magic" to seeing them as really just the simple devices that they are.

[@sergiosergioyou]

Very good explanation with electronics! Very good lesson !

[@djgforce1980]

Superb video, thanks Bruce. Keep up the excellent work.

[@DollarTreeFlyer]

wow thank you so much.. I have learned so much from you... worth more than I could afford for sure!!!!

[@letsgocamping88]

Excellent video Bruce, look forward to many more just like it :) Maybe also LC filters, pi and T networks and how they could be used. Maybe some more antenna themed videos like your cloverleaf video. Diy helicals, crosshair, patch and how they stack up....

[@marto2200]

Thanks Bruce really great info and well presented. Keep it coming its much appreciated cheers

[@jhonny001]

Great video, I'd appreciate more like this one !

[@b94cast]

These have been great, thanks a ton!

[@f18hornetm]

awesome videos. Please keep vids like these coming. I've always loved electronics but could never really come up with anything that useful. This stuff is awesome and is great practical electronics. Keep them coming!

[@mrcasehatter9580]

Thanks Bruce I can use that knowlodge in my OSD RSSI and won't have to buy the board for 25.00 + shipping from eagle tree lol..... Very well explain as well.

[@DayB89]

This was an awesome explanation. Thank you and congrats man!

[@TheRogerx3]

All ways happy to be educated, any form of indepth exsplanation is welcone.

[@WinstonSmith1984]

Good video. The only thing I missed was the explanation of why certain resistor values are chosen, and what the PWM frequency (typically) is, which is also related to the capacitor and resistor values.

[@jbx907]

T= RC, 1-20ms should be typical, it will depend on how fast you want your transient voltage to respond, attack and decay, those pulses would be 1520us as standard PWM would be unless the designer had other thoughts on that output.

[@WinstonSmith1984]

***** I think you're confusing RC PWM with non-RC PWM when you mention those pulse lengths. Anyway the frame length is relevant. That is 18ms or 27ms for FrSky RC PWM, but how long it is for the non-RC PWM used for RSSI on FrSky for example, I don't know, I've read 9us being mentioned.

[@itchyliabdo]

Very easy to understand. Thanks for sharing.

[@omega162]

That would be cool if Bruce made an Rctech channel that teaches you more in depth about the electronics.

[@ReggiePerrrin]

Great videos, but could you give us the formulas please to calc low, high and band pass filters? I know these can be found online, but you have a knack for explaining things clearly. I did all this years ago and have forgotten everything about them until your videos appeared...cheers

[@mjl0259]

Thanks for the explanation Bruce. After about 30 seconds I found myself staring at the screen and breathing through my mouth. I'm happy living in the land of, "Solder the gray thingy to the black bit" And of course that's solder without pronouncing the L. Everyone knows we Americans can't be bothered with that pesky L. ...s-ah-der

[@aesbj9228]

Thanks Bruce, I really enjoy your electronics videos. I'd like to see more so keep it up!

[@blackmennewstyle]

This channel is Art!

[@MrTaz0079]

Thanks Bruce, Please make MORE of these type of video's, You made it simple to understand, Now Iv got the basics(Thanks to you), How would I be able to integrate this onto a FRSKY V8FR-II 2.4Ghz RX for my APM 2.5 with the minim osd?? Please help

[@plowboyh6054]

Great video nice simple circuit using two op amps. Having worked with microwave telecom the noise floor was helped with negative voltage. Average voltage RMS. I would of loved to have you for a professor your explanation was much easier to understand the basics.

[@rctv-uk3126]

Loving this stuff Bruce. I feel a little smarter every time I watch on elf these. Maybe you should have been a teacher =D ATB Malc RCTV-UK

[@simonstuartmurray]

Really interesting. Thank you Bruce. Simon

[@bobbarlow1]

hi bruce, sheldon could not have explained it better !

[@louletuga]

Nice one Bruce!

[@youmanskids]

thanks Bruce, very well done.

[@pauljohnson7538]

I would use a small battery as an explanation instead of the balloon example. Longer pulses charging the battery to a higher voltage shorter pulses lowering the voltage. Thank you for your tutorials though always interesting

[@TimJC513]

Great video Bruce. How about making a similar video on using DC filters to reduce noise for FPV systems powered by the flight pack?

[@mscir]

Great explanation.

[@vlfreak]

cool vid bruce.. so simple :)

[@jamiedco]

please could you do a build of a low pass filter for rigging to your osd . i know its a simple build but it would be great to see how its done . last tine i tried it i made magi smoke come out of the low pass i built . thanks for another great video

[@gilgameshismist]

Love the T mate!

[@letsgocamping88]

And as others have said band pass filters for uhf etc, or what about saw filter upgrades? I'm interested in the real nitty gritty electronics stuff that rc has to offer. Allot of these equipment hacks make for better equipment and they teach allot in the process

[@KaffiFlight]

Hello Bruce - I´d like to have a description how to build a video transmitter that is compatible with 5.8Ghz ImmersionRC/Fatshark stuff. I guess you once have built some, but I guess not with legal frequencies for Europe. That frequencies ImmerisonRC uses are legal for us. Maybe there are many people interested in this, Fatshark/ImmersionRC is often used.

[@rhinenio]

Haha i love your big bang theory t-shirt huh huh

[@christophertelford]

I am currently building one of these myself. Google 'Make your own Diversity Video Receiver' and check out the multi-rotor uk forum thread. Full credit goes to Bruce at RCModelReview - thanks Bruce :-D I've modified the layout to build mine on pad board but it's otherwise the same.

[@rueda82nd]

My brain is hurting, thanks Bruce :)

[@Herman-iw3fj]

Hey Bruce, I like that your explaining how it all works but can you please put the schematics and parts list on your website so we can order the parts and get building. Also mad t-shirt, Bazinga!

[@Herman-iw3fj]

Never mind found the parts on your other videos description.

[@samp2806]

I think to cover more area you would want something that would handle 3 to 4 antennas. How would you add them to this design. it looks great and thanks to your wonderful instruction i understand what you have done but is it expandable and how.

[@byroboy]

Hi Bruce, Does the resistor used for the hysteresis affect the top receivers voltage in both states? As I see it, it keeps the voltage slightly higher when that one is on. When it has the lower RSSI (bottom receiver it being used), does it also reduce the voltage of the top receiver causing the top rssi to stay slightly lower?

[@jbx907]

In design we are assuming the rssi out is buffered or is a low impedance output, that's the whole point of hysteresis, it creates voltage offset from mid voltage. you got it right, you will need a slightly higher voltage difference between the two rssi out to trigger it to another state. I really wouldn't use hysteresis on a comparator for voltage comparison, probably on the next stage maybe.

[@zimmy1958]

loved every video you do THANKS!

[@helgewalle8862]

Thank you for all your informative videos, Bruce. I am interested in a signal generator like the one you show in the video. Is this readily available from shops? Helge.

[@Jporomaa]

Where were you at the physics lessons?

[@youmarchy]

You are the best - thx!

[@jbx907]

Nicely done Bruce, I'm still not satisfied with the 820k or hysteresis function of 820k, it will cause a certain voltage difference between comparisons, all we need is to adjust timing switching not voltage offset introduced by 820k. can you try removing 820k and replace it with the capacitor that is shunted to the ground in + input. instead of c going to the ground, place it to the output. this will cause a kind of timed hysteresis and offset voltages will not be fixed, but only for a time interval. the comparator will still compare perfectly.

[@jbx907]

Sir Bruce, and subscribers, pls don't miss judge my comments, I love your videos, and I want this, your design perfect without doing extensive math calculations. I'm just trying to remove the fixed hysteresis that gives offset voltage on the comparator, I hope you all understand!

[@xjet]

***** No worries.. the voltage offset is what creates the hysteresis. When the output is high, it provides a positive offset to the RSSI level on the +ve input of the comparator. When the output voltage is low, it provides a negative offset to the RSSI level on the input of the comparator. This means that the other RSSI level will have to be sufficiently different (even more high or more low) than + input in order to promote a switch and once that switch is promoted, it will have to differ by a similar amount to promote a reversal. This creates the hysteresis threshold. The 820K resistor in conjunction with the 4.7K input resistor produces an offset of just 0.6%

[@TheDk3bi]

Hi Bruce, veyry nice explanation. I would like to know how happy you are with the Rigol oscilloscope, because I want to buy one. Best regards, Udo, dk3bi

[@Les_Grossman]

Hi Bruce- Is that function generator usable? Which one is it exactly? Just was considering buying one, because my old one died and I did not want to spend a fortune ;-( As always: nice vid- worth watching even if you already know these basics!

[@leotl3368]

Thanks very much

[@ycopter]

Brilliant!

[@miroslavpokorny7145]

I suppose the delay of the smoothing is somehow related to the area under the curve aka using diff integration hence the name.

[@1winlock]

On a another video could you identify basic, intermediate and advanced level hobby test equipment. Thanks

[@MetaldetectingFriesland]

thanks it was very usefull

[@SGMasonKnives]

Very interesting, is this the same sort of thing that the DORA was to get a RSSI signal out of a Spektrum DSMX radio?

[@chinookmech]

Great bit of knowledge...how do I know what size capacitor and resistor to use? I want to get rssi out of my pwm into an osd.

[@impaler514]

Just got a college level class for free! Thanks a ton! You seem like you have experience in teaching. Were you a professor?

[@danpascu1482]

Nice !

[@robertboulanger8666]

The fact you mentioned OSD devices wanting analog is what I have been trying to solve as the turnigy 9X8Cv2 produces a digital RSSI but I can not find an answer to figure out the value of a resistor and capcitor to add to pin 11 to satisfy the OSD analog requirement so is there a good place to find a formula to guide me to this answer. THX thumbs up all the way LOL

[@cmavr8]

Great video Bruce! Is there any chance you could suggest a cheap oscilloscope and/or signal generator? I'm considering the DSO201 pocket oscilloscope but was wondering what your take is. We all know an RC/FPV hobbyist cannot afford a fully fledged bench tool, even the chinese ones... Thank you, Chris

[@cmavr8]

I'd like to add that I believe even a USB oscilloscope card would do the job for us occasional users. Commenting on the limitations etc would be nice :)

[@RobB_VK6ES]

Bruce, With the big day now seemingly very close I wonder have you given any thought as to the first model you will fly with your new wings? As a guess I'm thinking nothing too fast or expensive lest it fall to some rusty thumbs but you are probably over the AXN So I'm tipping the Caipirinha Anyone else care to take a guess?

[@noxnflame]

Hey Bruce great video! On your RX if you switch an aux switch what exactly would the PWM do? How easily would it be to create your own circuit that would activate a power load when a channel is switched on? Some thing that when, when hooked up to a transistor, could output a few amps of power but not through your rx.

[@RobB_VK6ES]

On a typical RC system all the individual channels are PWM modulated in a serial stream. The commanded servo position is determined by the width of the relevant channels pulse. It is the job of the reciever to first recover the PWM signal from the RF carrier and then to distribute the various pulses to the relevant channels. The servos then position themselves such that their internal reference matches the current PWM pulse for it's channel. Frequently on cheaper radios the channel allocated to retracts will not be proportional like the main gimbals. So in effect it acts like a on off switch but connected to a servo. Using a circuit almost identical to Bruce's Diversity controller shown here but adding a mid to high current transistor or mosfet as an output you will have a true RC power switch. you would simply need to set the bias resistors on the opamp to cause the switching at the desired PWM value. Having said all that there is little point in reinventing the wheel since such a circuit is readily available for very little money from Bruce's most loved/hated supplier :)

[@pavalige]

the new FatShark HD's are white Bruce! Your providing cheap R&D :-)

[@xjet]

Ah... so I'll have to paint my old ones to look trendy then :-)

[@pavalige]

***** They should send you a new set to review ...money well spent in my opinion

[@xjet]

pavalige Tell them :-)

[@michal.gawron]

For more ideal results just use low impedance caps (tantalum caps, for example). They'll charge/discharge faster. But in real life that wouldn't matter for a diversity controller, really.

[@WyllSurfAir]

Love It

[@MetaldetectingFriesland]

please make more wareplane videos if you could.

[@miroslavpokorny7145]

Is the size in mF of a capacitor linear ? eg double the capacity and the time over which the average is conducted is doubled ? eg if 0.1 averages the voltage over say 10ms will 0.2 double that time so the line travels the average more slowly ?

[@jbx907]

the charge and discharge is not linear, but when talking about T, it is linear, doubling the capacitance in general will double the time it averages.

[@LeviathanFPV]

What resister and capacitor are you using?

[@dave_s_vids]

Very interesting, thanks! More please :)

[@TheFarleyGordon]

Thanks Bruce I love this stuff only wish I could understand better. Not very smart I'm afraid. Say Bruce or anyone I bought a APM 2.6 and need a APM Power Module the question should I buy one without a BEC or the one with a BEC for my FPV and Min OSD. Has Bruce done Vids on setup of The APM. Cheers Mate

[@waynesmith7592]

APM 2.6 power module has BEC to power the controller. It is not used to power servos.

[@MatHelm]

What are your thoughts on your oscilloscope there? Good, bad etc.. Would you buy it again? Thanks for all the vids...

[@xjet]

The Rigol 1052 is getting a bit long in the tooth now but it's still a very useful bit of kit. Check out Dave Jones' EEVBlog for some scope reviews and information that you'd almost certainly find useful if you're in the market for a digital storage oscilloscope: kzbin.info

[@MatHelm]

Thanks for the link, but I was speaking of your DS1052E..... edit: Ahh... lol Didn't see the Rigol part

[@bgdwiepp]

But bruce, what about an inductor instead of a resistor?

[@xjet]

You can use an inductor but at the frequencies we're talking about here (relatively low, probably between 1KHz and 100KHz) then the value of the inductor would need to be pretty high to achieve the same effect as the cheap, light resistor :-)

[@Ibushi]

I read that we need to make a converter to be able to hook up the Frsky RSSI to an OSD. Is this it?

[@Ibushi]

***** Cool. Thanks.

[@MrTaz0079]

***** , Hi would you be able to expand on your reply please, Ie, what rx?resistor and a capacitor values?? or if you did a build log...... Please...

[@benjahnz]

Looks like LP filters on the inputs to me.

[@SladkaPritomnost]

your signal is going below 0 that's not quite correct (for rssi), great video btw.

[@virtuosomuso]

Bruce is the capacitor acting like a compressor then

[@mxman69]

more like an accumulator :)

[@youmanskids]

I like to think of it as a small/fast little battery, takes a charge and gives it back very rapidly.

[@yaghiyahbrenner8902]

im confused. how is that integrating ?op-amp is connected in differentiation mode. the input is a RC low pass filter. www.electronics-tutorials.ws/opamp/opamp_6.html

[@thomasphillips885]

Isolate the capacitor-resistor network www.physics.ucla.edu/demoweb/demomanual/electricity_and_magnetism/ac_circuits/rc_integration_and_differentiation.html The RC low-pass filter is actually doing the integration

[@yaghiyahbrenner8902]

***** Ah thanks for clearing that up I see what you mean, I was looking at the RC filter and realised that's the case .I was thinking of an op-amp used as an integrator. not the front end part.

[@MorningView]

rofl your lack of political correctness is enlightening