Wiring 2 LED's in series.

[bipeflyer]

Hi,I have 2 ultrabright LED's 5mm dia. rated at 1.8 v each,and 50mAh draw.
I want to wire them in series with a microswitch in the loop,so I can install them in my SU.27 Flanker pusher electric.I want to emulate afterburning,so they will be buried in the tailpipes.(just for fun)

My question:
Could someone reccomend a power supply,I was thinking of using 2 AAA NiMh batteries.Would that be too much,if so,what can you reccomend please?
A small drawing would be appreciated,bearing in mind I am no electronic expert!
Many thanks in advance,
Matt.
Here is a photo of the model:
Power from a Mega 15/16/4,30 Amp ESC,10 CP1300 cells.
Taileron control only,handlaunched.

[steve lewin]

If you wire them in series you need 3.6V (1.8V x 2) so 2 NiMH cells is a bit low. It's also a good idea to include a current limiting resistor in any LED circuit. I'd just wire them to the battery you already have in there with an appropriate resistor.

For a 10 cell (12V) battery use

12 - 3.6 /.05 ohms = 168 ohms, nearest standard value is 180 ohms (at least 1/2W rating).

An alternative would be to use the 5V supply to your RX/servos either from BEC or a 4.8V battery. If you use that you will only need a 27 or 30 ohm resistor.

Are you intending to switch these on and off in flight ? If so how will you drive the microswitch ?

Steve

[bipeflyer]

Hi Steve,thanks for your reply.The microswitch will be linked to a servo,so with up elevator applied it will activate the circuit.The horn(opposite side) will be cam shaped,to avoid stalling the servo,at a predetermined length,it will strike the microswitch arm.

I have a load of old railway controllers,with LED's in the circuit.Could I remove a resistor from one of those,and does it state on the resistor the impedance?
To clarify,I need a resistor with 180Ohms using a 12V supply?

Alternatively,could I not use 3 AAA cells,and plug in using a BEC style parkflyer plug and socket?

Forgive my ignorance,my knowledge of electronics wouldn't fill the back of a stamp!
I really need some kind of illustrative drawing to show the wiring sequence.
I understand that above 5v it is possible to blow the LED's if reveresed in polarity,but below 5v this won't happen,can you concur?
Are the NiMh cells not 1.2V each?
Many thanks for your assistance,it is truly appreciated!
Matt.

[Bill Glover]

Mr RC-CAM set up this fantastically useful website - just type in the specs. of your LEDS, how many of them in series, and what voltage supply - and it tells you what resistor you need (and even what the colour code for it is)!

http://www.rc-cam.com/led_info.htm

I'm in the process of fitting ultra-bright LEDS to my Twin Star right at the moment. Out of interest, I have a single white one in the nose (mounted in a tiny reflector from a single-cell AAA flashlight) - that's just wired to a spare RX outlet. I have 3 wired in series on each wingtip (LE facing forward, TE facing back, & tip facing sideways - red on left wing, and green on right) - these are driven by a feed from the 8-cell flight pack. Basically you want to use as few resistors as possible as this is wasted energy (albeit only tiny amounts :) ) - you might as well use another LED instead if you can.

Anyway, RC-CAM's site (above) was a HUGE help in figuring all this out.

[Bill Glover]

PS I got my LEDS from Maplin, where the Maplin site didn't quote the necessary technical information (e.g. forward voltage & current) a Google search on the maker's part number (for example: Toshiba TLSH180) found it within minutes.

HTH.

[bipeflyer]

Thankyou Bill-I bought mine from Maplin too,the Southend branch is at the end of my road.I got the ultrabright in orange.
I'll do a google search later to track them down.

I will also check the RC CAM site as you suggested,should be able to light those fires soon!:)
I take your point regarding the resistor sapping current,but if it will prolong their life,may as well go for it,then I will butcher those old Hornby railway controllers.I used to work in a hobby shop,they were obsolete items,the boss launched them into a skip,but I rescued them,thinking they might come in useful someday (got about 20 of them)

Are you going to fly your TJ in the dark?The nose light will sure be bright!
Good luck with it.

Matt.

[Bill Glover]

Originally posted by bipeflyer
Are you going to fly your TJ in the dark?

No, the lights are on my Twin Star .. not the Twin Jet (now that really would be a challenge in the dark :D ) !

In the summer I quite often fly the TS at dusk on a local sports field (when it's deserted). I've always had some dayglo yellow trim on the wing LE, when the light is failing that's about all you can see when on finals! So the lights should come in handy (as well as just being a neat thing to do!). I do actually have a spare HS50 servo and some microswitches, so "phase 2" will be to make them switch on and off in flight :cool:

Good luck with your project.

BTW Maplin online is very good, I do have a store near where I work in London but they only stock a fairly limited range. Post and packing is normally only about £2 and so far stuff has always arrived through the door next day!

http://www.maplin.co.uk/

[bipeflyer]

TLRH180P
Hi Bill,sorry,my mistake,I have TJ and it must be on my mind!

Anyway,I got onto RC CAM's site and conducted a calculation based on my bulb (TLRH180P) and forward current,and current draw-I was wrong,it is only 20mA.

I need a 150ohm,1/8 watt resistor,Brown Green Brown.
I'm going to rip apart a transformer tonight,if I don't find one,then it's up to Maplin again tomorrow.

My local store is very well stocked,as it they started in Southend,I guess it would be! (don't know how lucky I am,do I?):)

Thanks a lot for the tip,I'll let you know of my results-I plan to run it through my RX as suggested,it has a BEC ESC running it.
Give the microswitch a try!
Cheers!
Matt.
PS Just found this link too:
http://www.xs4all.nl/~erix7/models/leds.html

[RMihara]

You may want to consider using my SMT Switch™ (http://www.rcgroups.com/forums/showthread.php?s=&threadid=83291) for this application. Using a Y-lead you can set the switch to trigger off max throttle thus illuminating your LEDs.

Regards,
Roger

[BMatthews]

Very nice switch there Moose. Looks and sounds first rate.

Bipeflyer, you'd better listen to Steve. The resistor value must be locked to the battery voltage to ensure that the correct current flows through the LED's. You can't just pull one from another circuit unless the other circuit uses the SAME voltage and SAME number of LED's that need the SAME current to light up. If you ignore this then you'll either get poor light or you'll let the smoke out.... :D

An analogy that I llike to use is to compare electrics to plumbing. Voltage is the same as pressure and current is the same as gal per minute. Resistors are like preset valves and potentiometers are like adjustable valves. If you look at it this way then you should see that each resistor will flow so may gpm depending on the pressure. Up the pressure and you get too many gpm and the led's are overloaded. Too little pressure and you don't get enough gpm to light them up right. So I hope this shows that you can't just mix things up and expect them to be the same.

If Radio Shack doesn't have resistors any more (they seem to be selling less and less components these days) then look up a proper electronics outlet in your area. If that doens't work you should be able to buy the one resistor you need from a TV repair shop for 50 cents or so. That price is highway robbery but that's how much they will probably charge you for bothering them. Or if they give it to you for free promise to bring in your broken TV next time.

And while you can get pots that are adjustable unless you have a meter to set the current then you're playing with fire.

Oh, and while we are at this. I trust you do know that the LED's have a + and - side that need to be hooked up correctly? If the voltage is low then you won't blow them by hooking them up backwards but if it's higher then it's possible to damage them. Look for the max reverse voltage to know if you're playing safe or not. It'll be in the spec sheet.

[Bill Glover]

Originally posted by bipeflyer
I need a 150ohm,1/8 watt resistor,Brown Green Brown.
I'm going to rip apart a transformer tonight,if I don't find one,then it's up to Maplin again tomorrow.

My local store is very well stocked,as it they started in Southend,I guess it would be! (don't know how lucky I am,do I?):)


Sounds good. I got my resistors from RS Components:

http://www.rswww.com/

Maplin only seemed to sell packs with thousands of mixed resistors in (for 'projects' etc.) whereas on RS you could pick the specific ones you wanted (sold in packs of about 10, costing pennies).

PS I have TJ, TS, and PJ ... I know it's very easy to type the wrong one :D

Roger - very nice unit!! I will certainly remember that for future projects.

[steve lewin]

Maplin will cheerfully sell components including resistors in ones, even via the Web, though like RS the post and packing is a bit much if you only wanted a 2p resistor ;).

It is a lot easier if you have a convenient local Maplin store. Unfortunately my local one seems to have a fixed policy of being out of stock of at least half the components I want so I end up at RS quite often too. RS also have a much wider range of stuff, like IR receivers, Li-ion charger ICs and decent MOSFETs.

Steve

[BMatthews]

Ya know with all this talk about the electronics and thinking how neat it'll be to see those "afterburner light" I think everyone has forgotten about the pic of that Oh So Kewl MODEL....:eek:

Bipeflyer, how about more info on that Flanker? Kit or plans? Own design or...? Looks like a carved foam fuselage. Fiberglassed to hold those cells of just a skin over a wood foundation?

It's super cool and lovely craftsmanship in any event.

[bipeflyer]

Thanks everyone for your great help.I'm off to the component store tomorrow to pick up the correct resistor.

The model was built really for an experiment with building.I normally design my own models,meaning laborious drawing measuring etc.On the flaker,being so curvy,it would have taken forever to draw.
I had an idea that I would build it without plans using a constructed plastic Italeri 1/72 scale model.

This is how you do it,if you'd like to know more:

For example,a wing: place a piece of foam slab on the floor.Work out the wingspan you want,them mark the length off on the foam with a pen.
Then hold the plastic kit wing over the slab,mark off the corners.Take your time here to get it right.Note each corner on the foam,pick a visual reference,pice of dust,dent,etc,and mark off each corner.Join the dots with a pen,and cut out!
Do the same for the fuse,stabs,etc.KEEP CHECKING!

Fuselage: I laminated a piece of foam above the slab to reach the upper surface,so overall your fuse is the correct depth.Only glue in the centres with epoxy,or whatever,as glue lines are impossible to sand off!
Take your plastic kit again,establish the detailed areas with a pen,and draw rough carving lines and carve!
There is a hell of a mess in the process,use a ventilator.
I will experiment next time with a vacuum cleaner with a funnel in the end,and carve over that next time!

Use a surform to rough out,then a Dremel tool with a sanding drum atttachment to do the cleaner work near the surface.Refer to your plastic kit regularly,as this is all done by eye.

When near the surface you want,sand with various grades of paper.
The underside motor 'tubes' were made separately,then hollowed out before sticking on,also the area out of sight undeneath was hollowed too,beforehand.
Use reference lines continually throughout to prevent,' bananaing'
the fuse.

The wings were built over the foam slab as a 'plan' from 6 ribs per side,an MH 22 modified section from Profili.
Just divide up the blank to evenly space the formers,and draw on the foam.
Tailparts are sticks covered in 1/32" balsa,then sanded to section.

I must say,I'm extremely pleased with this experiment,and plan to build more models this way,it's fantastic-no plans at all!(in the conventional sense!):D

It's not exact scale,but captures the lines of the full size machine very well indeed.
Model data:
W/S 25"
Power: Mega 16/15/4
10 CP 1300 cells.
30 Amp ESC.
Taileron control only.
Finish: Tissue/aliphatic watered down.
Colour scheme : Russian Knights formation aerobatic scheme,using acrylic paints.
This is the current progress:

Matt.
Someone else try it-you won't be dissapointed.I might build a B1-B next.

[bipeflyer]

'Fly by...........'

[bipeflyer]

Side on.....

[bipeflyer]

Another..

[bipeflyer]

Hollowed out underside with carbon roving local support.

[bipeflyer]

Last one.
To follow this project through to completion,I have a thread going in the 'Foamies' forum entitled: 'Foamie Flanker!'

Thanks again for all your wonderful help,very much appreciated,and thanks for taking time out to help!;)

Matt.
www.geocities.com/grumman_uk

[BMatthews]

Yer an inspiration, that's for sure. I'll be watching that other thread for flight reports.

I've got a 25 inch span F18 that's done in balsa sort of like your Flanker. Meant for a Tee Dee in the nose and the gear in the tail. Scale fuse length. Been ready to cover for about 14 years.... I really got to get past that builder's block....

[bipeflyer]

Well,I hope you feel inspired enough to finish your little F-18,14 years is a long build;)

Picked up my 150 ohm resistor today.I forgot there is a guy that runs a small radio shop around the corner from me.
Cost me all of 5 pence for the brown/red/brown resistor!

When they are installed and alight,I'll post a picure here.
Thx again!
Matt.

[bipeflyer]

Well,I just soldered up the LED's in series with the 150 ohm resistor,plugged the lead into a spare rx slot,actuated the microswitch lever,guess what?
IT WORKS!!!!!!!

I am very impressed,but not as bright orange as I hoped.I chose the resistor using RC CAM's site calculator too.
Do you think I may have the wrong resistor?

Could it be brighter do you think?

Matt.

[bosley]

That looks great to me! Especially if you were flying it near dusk. Awesome looking plane too.

Boz

[Bill Glover]

Originally posted by bipeflyer
Well,I just soldered up the LED's in series with the 150 ohm resistor,plugged the lead into a spare rx slot,actuated the microswitch lever,guess what?
IT WORKS!!!!!!!

I am very impressed,but not as bright orange as I hoped.I chose the resistor using RC CAM's site calculator too.
Do you think I may have the wrong resistor?

Could it be brighter do you think?

Matt.


Matt, if your LEDs are TLOH180P (you mentioned TLRH180P, but those are red and I thought your were orange) then they are rated for forward voltage of up to 2.5V. So to run two in series from a 4.8V RX supply no resistor is required at all ... which would explain why you think they look a bit dim!

See

http://www.jameco.com/Jameco/Products/ProdDS/131895.pdf

for the specs.

[bipeflyer]

You're right Bill,I copied the wrong code,it is TLOH180P,what an idiot I am,should have cut and pasted it.
No problem,the resistor is buried directly under the skin,I'll dig it out of the foam,desolder it and reconnect.
Hopefully there will be a bigger blast of light in store!

Looking on the brigt side,I get to shave off some weight with it's removal.:rolleyes: (I wish...)

Thanks for putting me right,and apologies for my stupidity.Now I know it will be ok!
Where would we be without the Ezone?
Regards,
Matt.
I'll let you know tomorrow how it goes.
Just weighed it,with two servos,(HS 80MG) and the LED system installed,it is 8 oz!:D
Should go alright!

[Bill Glover]

Good luck. If I get time to install the switch servo (and the weather is flyable!) I should be able to try out the lights on my TS tomorrow. Not quite as sleek as your SU 27 and a little bit heavier too (due to the 7 LEDS of course ;) )!

[bipeflyer]

Well,good luck with that Bill, can you post some pictures of it in operation?
I hope the weather co operates too.

Matt.

[BMatthews]

I dunno about this guys. LED's with no ballast resistors are a risky proposition. I wouldn't be surprised if a fully charged battery overloads them. You may still need a 5 or 10 in there for a safety with full charge voltages.

[Bill Glover]

Matt is running off the RX (i.e. using power from the BEC) ... so the voltage should be pretty constant.

[Bill Glover]

Well I finished the lights on my Twin Star, here are a few pics.

R/c bay is a bit more crowded now, there's an HS50 servo mounted upside down in the top right of the shot. This has a microswitch fixed to the side and operates the lights via an aux. channel from the TX. The red BEC plug is the connection to the wing. The blue plug is the normal aileron flylead.

[Bill Glover]

Power is fed back through thin wires added to the ESC input leads.

[Bill Glover]

Nose 'landing' light, white LED in a reflector from a tiny flashlight. 220 ohm resistor in series ;)

[Bill Glover]

Switched on, very bright if you look down the beam (too bright to photograph!).

[Bill Glover]

3 LEDS in series on each wingtip, 120 ohm resistor. Left & right wings are wired in parallel (like the motors). Here are the LE and tip lights on the left wing - red this side, green on right wing.

These LEDS are very directional, they each project a circular patch of light onto the wall when you switch on!

[Bill Glover]

And finally the TE light, just inboard of the aileron.

I also have some 10mm red flashing 'hyper bright' ones so may eventually put a flashing 'beacon' light on the fin and/or under the fus.

[bipeflyer]

Looks good Bill.The noselight looks super bright,let me know how it looks in the sky,pics. too if you can manage it.;)

BTW Those pictures are superbly clear,what camera are you using,wish mine were as good!How many pixels,etc.

I am ripping out the resistor today,I'll post a new picture later.
One thing that puzzles me,the LED's I have are completely clear,before I tried them,I thought I had been sold the wrong bulbs.
Is it a chemical that reacts with current that produces the colour?
Just curious really.

Thanks,
Matt.

[Bill Glover]

Yes, the red/white/green LEDs on my TS are all the 'clear' type - I've no idea how they work either!

Well the TS looks great in flight, the lights are clearly visible ... even in this afternoon's bright conditions. Once the sun started to go down, cruising round low & slow with the lights on was fantastic (for anyone who hasn't seen it, my TS has radial cowls, gearboxes, 11" props, and a trike u/c :) ). I was going to get someone to take a few pics ... but ... had a mid-air with a .60 IC model :eek: ! Very minor contact, I landed to check the model over but the other guy didn't bother. Just as well I did land, one aileron horn had been pulled completely out and the pushrod was swinging from the servo arm. That was the only damage, took 5 mins to epoxy when I got home but that's why no in-flight pics!

I mostly use a Sony F717 camera. It's 5 megapixels, but that's pretty academic as far as posting stuff on the Forum goes! For that I resize images down to about 600 pixels across, and then compress to give a size of 30-50 Kb. It does have a great lens though, which helps a lot.

[Mr.RC-CAM]

Is it a chemical that reacts with current that produces the colour? Colors are the result of the visible wavelengths emitted by the chosen semiconductor material.

As far as operating with no series resistor, I am with BMatthews. I ALWAYS use a resistor. Why? The LED forward voltage can vary several hundred millivolts between identical part numbers. The Vf is also temperature dependant.

If it was me, I would use at least a 22 ohm series resistor in those situations that seem to not need a LED current limit resistor. Put it close to the BEC if you can.

Just consider it insurance for the BEC and the LED.

RC-CAM

[Dax]

ALWAYS use a resistor with led's

Do what I did, use a potentiometer ($3) its a variable resistor, I just turned it up and up and up till I blew up the LED, then I turned it down a bit and replaced the LED. I figgure I a damaging the LED's and shortened their lifespan by a factor of 10, but they are damm bright!


Also, not only are LED's tempreture sensitive, but they are photosensitive. That is, they work like a photo diode, there resistance value goes up the more light is shined upon them.

You can mesure this with a multimeter, its actualy prety cool!

[bipeflyer]

Thanks again for the advice,I'm curious-if I refit a resistor,can I put it somewhere in the fly lead from the rx port?

It would be difficult to actually put it in the circuit,as it's all closed up now,and inaccessible.
If so,does it matter to what lead (-ive or +ive) ans is it best positioned well away from the rx?

I wiil get a 22 ohm resistor to install,if that is the correct one.

T.I.A,
Matt.

[Mr.RC-CAM]

As mentioned on the RC-CAM "LED Calculator" web page, you can put the resistor on any lead. Basically, it can go anywhere -- it only needs to be series connected.

However, I recommend that it be placed as close to the Rx/BEC as possible. That way, if the LED's wire harness is shorted, the BEC is not brought down to its knees. With 22 ohms on 5V, a shorted cable will only draw about 225mA.

Regards,
Mr. RC-CAM
www.rc-cam.com

[bipeflyer]

Many thanks!
I can solder in confidence now.:D

I hope I can see these darned lights outside ok after all this (I mean in overcast conditions)
Cheers,
Matt.

[Bill Glover]

Well I finished the Twin Star setup last night by adding a couple of big (10mm) red flashing LEDs (clear, ultra bright) on the fus.

These are rated at 9V, so wired in parallel with a single small resistor (57 ohm) in the circuit.

Ideally one would have gone on top of the fin, but that's where the aerial runs ... and being a paranoid sort, I wanted to keep the wiring well away from that! So one went mid-way along the dorsal strake, and one directly below on the fus. underside. Managed to run the wiring along the channel where the elevator and rudder snakes go, so all concealed :)