Now OnLine: LED resistor calculator just for R/C'ers

[Mr.RC-CAM]

There have been several posted requests for help with determining the current limiting resistor value for use with e-flight LED's. To folks not in the electronic business, the required formulas are like witchcraft.

To help out, I created a custom app that computes the resistor's ohms and watt specs based on three things: [1] Battery voltage, [2] LED forward voltage (from its data sheet), [3] and the current you would like to use.

The results even tell you the Digi-Key and Mouser part numbers to buy! I really like this little feature.

The app is fresh out of the oven. I would appreciate a sanity check from those of you that are LED saavy.

Click for RC-CAM's LED Calculator (http://www.rc-cam.com/led_info.htm)

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

[ElectriFan]

Looks great!!

Need a question answered to 'illuminate' my brain ;)

Since the angle of light beam from an LED is in the 25-40 degree range, often we mortals want/need 2 LEDs - one on top and one below (prolly different colors) to help identify the orientation of the plane. If I use the 5th channel on my Flash 5X to switch it on/off, and have one big loop to connect 6 LEDs in series (a pair of LEDs in 3 locations - wing tips and nose), would I use the same resistor calculated by this app? Or do I need to add all the voltage and/or current values together? Another layout would be to have the pair at each location in parallel, which changes the formula and result.

[dbx824]

Can you power LEDS directly from an empty receiver channel connector so you can switch the lights off and on? A little explanation on how receivers work and what the ouputs are would be great. Thanks.

[Mr.RC-CAM]

...and have one big loop to connect 6 LEDs in series (a pair of LEDs in 3 locations - wing tips and nose), would I use the same resistor calculated by this app?For series connected LED strings, you would add up the series connected LED Vf values and enter it as if it was one big forward voltage spec.

Here is a typical e-flight example where two LED's will be paired up via a series connection: 7.2V battery source, 2 each LEDs with Vf = 1.7V, current desired 20mA.

Enter Source voltage as 7.2
Enter LED Vf as 3.4 (Note: 2 x 1.7)
Enter Current (mA) as 20.
Result = 220 ohms (next standard value, as determined by the calculator).

Each series connected LED pair gets its own resistor. Do not share this resistor with the other LED pairs.

With a high enough battery voltage, you can use one resistor with several series connected LED's. The calculator checks to see if your data is valid, so entering values that will not work correctly will provoke a helpful pop-up message.

Regards,
Mr. RC-CAM

[Mr.RC-CAM]

A little explanation on how receivers work and what the ouputs are would be great. There is a lot of info scattered about eZone on how to share the Rx power. However, since you asked, I just added a few simple words on the calculator page. Please see "How Do I Power My LED."

RC-CAM

[Bill Glover]

Excellent app. - really helpful!

[ElectriFan]

Thanks RC-CAM. I think I got it.

So for a 6 LED (3 red: Vf=2.1, Current = 20mA, 3 green: Vf=2.1, Current = 20mA) circuit connected to an 8x pack, I will need a bigger battery, or break it up into 2 circuits of 3 LEDs.

If I use a circuit of a pair of blue/red LEDs (red: 2.1V, 20mA, blue: 4.1V, 25mA), I guess I can use the higher current value (25mA) to get a 240ohm, 1/4 watt resistor and still not burn out . Right?

[ElectriFan]

However, do not overload the BEC with too many lamps or you may loose control of your model during flight. The number of LED's you can connect will depend on the BEC's current rating, number of servos, and LED current draw. Please do not ask me for advice on how many LED's your ESC can handle -- I will not know.
Ah, looks like a great idea for another app?;)

[Mr.RC-CAM]

So for a 6 LED (3 red: Vf=2.1, Current = 20mA, 3 green: Vf=2.1, Current = 20mA) circuit connected to an 8x pack, I will need a bigger battery, or break it up into 2 circuits of 3 LEDs. Yes.

If I use a circuit of a pair of blue/red LEDs (red: 2.1V, 20mA, blue: 4.1V, 25mA), I guess I can use the higher current value (25mA) to get a 240ohm, 1/4 watt resistor and still not burn out . Right?Let's see. 2.1V + 4.1V = 6.2 (series connection). 8-cell battery is about 9.6V or so. 25mA current. The calculator says to use a 150 ohms.

You do not need to use the higher current if you have "mixed" LED's. They will tolerate lower currents at the expense of brightness. Never exceed an LED's max current rating.

RC-CAM

[ElectriFan]

In the second scenario, since the red LED is rated lower, I would go with 20mA, hence an 180 ohm 1/8 watt resistor.

1. The resistor comes first in the circuit, does the sequence of the LEDs matter (4.1V LED before the 2.1V LED or vice versa)?
2. Last thing one would want is for the plane to fade away shortly after launch/ROG. What luminosity LED is sorta the minimum for a parkflyer (single, double, triple or quadruple digits)?

If it's not obvious already, I am really looking into lighting up one or more of my planes.:D

[Mr.RC-CAM]

1. The resistor comes first in the circuit, does the sequence of the LEDs matter (4.1V LED before the 2.1V LED or vice versa)? No. The electrons are stupid.

thing one would want is for the plane to fade away shortly after launch/ROG. What luminosity LED is sorta the minimum for a parkflyer (single, double, triple or quadruple digits)?That is the big question. I suggest you play with >3000mcd with at least 25 degrees viewing angle.

RC-CAM

[Mr.RC-CAM]

The Netscape bug is fixed. Whew!

RC-CAM

[ElectriFan]

Got it. Thanks RC-CAM. Did I say 'awesome job'?

No? AWESOME JOB, RC-CAM!!

[Andy W]

That's pretty darned impressive. I looked at the code and that's pretty slick.

With the calcs you have, could you make a series and parallel calculator too (multiple LEDS in series, with parallel strands, as used to light up entire models)?
..a

[Mr.RC-CAM]

With the calcs you have, could you make a series and parallel calculator too (multiple LEDS in series, with parallel strands, as used to light up entire models)? Yes. But it can be done now using the app's basic features.

Just add up the consectutive Vf's and enter the result as a single Vf value in the calculator. Do this for the series LED's only. Treat each series string as a little sub-assy, then join then all in parallel when you stage everything together (when it is installed in the model). Don't worry -- The calculator will make sure that you don't try fitting ten pounds of LED's in a five pound bag. ;)

I never thought that there would be THAT much interest in this little calculator. I figured that there were a couple of LED-impaired folks out there that wanted to use them but were intimidated by the math. My intent was to remove that little bug-a-boo.

I would rather not be the resident LED guy -- there are better folks out there that deserve that title.

I looked at the code and that's pretty slick.The gentleman that I credit on the calculator's web page deserves all the credit. His basic java code gave me the inspiration to it all.

Mr. RC-CAM

[Andy W]

I didn't read the whole thing, so I missed the credits! :) Either way, I was impressed. Didn't know you could do all that in html..
..a

[Neil McGrath]

Looks like a useful feature - well done.

For those who find the whole concept of fitting a series resistor a bit daunting there is an alternative.

http://www.maplin.co.uk/products/Module.asp?CartID=0210040809071451110&moduleno=2054&modulecode=

Neil

[Bill Glover]

Originally posted by Neil McGrath
For those who find the whole concept of fitting a series resistor a bit daunting there is an alternative.



Neil, those are only available in 5V and 12V ratings ... so not that useful unless you are running 4 or 10 cell packs!

They are also not the 'extreme brightness' type that are most useful for models. I bought a load of different ultra-bright LEDs last week from Maplin, some of the flashing ones are rated at 9V anyway so can be connected directly to a 7 or 8 cell pack. Many of the others (especially the expensive 'clear' red, green, and white ones) are rated at only 2.5-3V and so this online calculator is a great help!

[Mr.RC-CAM]

The web page now has an "LED Roundup" section that provides good/better/best ratings on several affordable choices.

I need to finalize the info on some Digi-Key LED's, so check back in a few days. But what is listed now offers plenty of data for most R/C model lighting applications.

My PIC microcontroller based R/C navigation light control system will be published soon too. Just check the web site's "Project Page" at the end of the month: RC-CAM Projects (http://www.rc-cam.com/projects.htm)

The Nav-Lights gadget has remote activated landing lights (via throttle stick or spare channel), anti-collision strobe, wing tip lights, and a handy R/C signal glitch counter. Cost for the Digi-Key parts is well under $10 (+ the cost of the LED's you use).

Regards,
Mr. RC-CAM

[Flying Taco]

www.superbrightleds.com is an excellent source for leds with fast shipping. They have up to 10,000mcd intensity. The 8000mcd red and green ones are very visible.

[stevem1928]

Mr RC, I am anxiously waiting for Nov. 1. The release date of the Nav. light tutorial. Several of your projects are on my winter To-Do list. The Nav lights will be the first project. Thanks for making this info. available. You have very clear & complete insturctions.

Do you have a sneak preview of the parts required? I would like to have them pre-ordered if possible.

What is the normal configuration of airplane lights color and location?

[Mr.RC-CAM]

... I am anxiously waiting for Nov. 1The Nav-Lights project is online. I posted the web page last night.

It has links to some info that describes normal aircraft lamp color configurations.

RC-CAM

[Flying Taco]

Thanks for sharing your hard work with us!

Now in order tomake this system work I need to purchase or build a chip programmer, correct?

Will this one work? http://www.poptronics.com/interactive/FreeProjects/MultiChipPgmr/MultiChipPgmr-P1.html

I've never built anything that required programming but I may give it a shot. I like a challenge.

[Mr.RC-CAM]

Will this one work? It looks like a very basic PIC programmer and should do the job.

If you build this PIC programmer please post how it worked out for you. Oh, and please report back how you like the Nav-Lights gadget -- hopefully it is given a thumbs up.

Mr. RC-CAM

[stevem1928]

It looks like my winter project list will now include a PIC programmer. Can one of these programmers be bought? If so, how much are they? The plans for the programmer look more involved than the Nav lights. I like a challange.

I will have a big supply order when I order the parts for my video camera, Nav lights and programmer.

The extra devices on the Nav lights are really nice. Especially the lost plane alarm.

Thanks Mr. RC-Cam.

You obviously have a lot of knowledge in this area.

[stevem1928]

I found the pre-made PIC programmers on the above mentioned site for ~ $25 shipped. The kits are ~ $20 shipped. I like a challenge and will try to build one from a kit.


http://talking-electronics.tripod.com/cgi-bin/Buy-Pgmr_Lab-1.html

[Mr.RC-CAM]

If you wish to buy from a USA source then this $15 kit is popular: http://www.electronics123.com/amazon/default.htm

You will also need the picallw.exe software upgrade (additional $25) to program the PIC12C508 parts.

I have not used this one either, but those that have were happy with it. For hobby use, skip the expensive ZIF socket.

Regards,
Mr. RC-CAM

[stevem1928]

The above site lists another item called PIC Lab-1. Could this device be used to put a .wav file onto an audio greeting card that uses a device like the one pictured below? The compact sound systems have been discussed briefly in this thread.

http://www.rcgroups.com/forums/showthread.php?s=&threadid=64772

I am trying to justify spending $20-$25 for the PIC programmer. I'm just not sure if I need to be spending the $ for something that I will use once. Is there any other uses for the PIC programmer?

[Mr.RC-CAM]

Is there any other uses for the PIC programmer?There's lots of uses as long as it involves programming a PIC microcontroller. :)

Nearly all of those recordable modules are using the ISD series of voice chips. Some of the ISD products are self-contained, others need microcontroller support. None will connect to a PIC programmer. ISD/Winbond info www.isd.com

[MrBungle]

Originally posted by Flying Taco
Thanks for sharing your hard work with us!

Now in order tomake this system work I need to purchase or build a chip programmer, correct?

Will this one work? http://www.poptronics.com/interactive/FreeProjects/MultiChipPgmr/MultiChipPgmr-P1.html

I've never built anything that required programming but I may give it a shot. I like a challenge.

Originally posted by Mr.RC-CAM
It looks like a very basic PIC programmer and should do the job.

If you build this PIC programmer please post how it worked out for you. Oh, and please report back how you like the Nav-Lights gadget -- hopefully it is given a thumbs up.

Mr. RC-CAM

Yes this programmer works fine, I have been using it for a number of years.

Flying Taco, note that the 10uF capacitor will need to be replaced with a 100uF one.
I scratch-built one from that design, but it couldn't program my chips, so I figured it wasn't generating enough programming voltage with the 10uF and replaced it with the 100uF, it has worked faultlessly ever since. Colin from Talking Electronics(the site owner) might have replaced these in the kit versions.
BTW, I discovered later that the designer of that programmer shows a 100uF cap on his website. http://www.jdm.homepage.dk/newpic3.htm

For a long time I used the DOS based pip-02 programming software. Its works but its a bit of a pain to use.
Just recently I changed to the free ICPROG windows software available at the address below. Never had a problem with it.
This software is not just for PIC's but can program almost any serial eeprom, some of the AVR devices, and the Scenix range of devices, and can also be used with more than a dozen other programmers, like the David Tait designs for example. (Click on the screenshot of the software to get to the downloads page) http://www.ic-prog.com/

Simon

Doh! I accidentally sent this prematurelly and didn't realise, then sent a second revised copy of it ... grrrrr

[Flying Taco]

Thanks for the heads up Mr. Bungle. I'll order the parts when I get bored.

[MrBungle]

oops, posted the wrong link to the designer.
http://www.jdm.homepage.dk/newpic.htm
The poptronics/TE site doesn't mention it, but this programmer will program any of the following PICs (and eeproms):
PIC12C5XX, 12C67X, 24CXX, 16C55X, 16C61, 16C62X, 16C71, 16C71X, 16C8X, 16F8X

I'm going to try a 12CE51X (serial eeprom version of 12C5XX) with it soon, checking datasheets to see if it will work okay.
Hope I don't pop my $20 windowed version! :eek:

Note that it doesnt have to be built with the 25pin connector and can be built as a 9pin serial version.
My 'puter doesn't have a 25pin serial port so I went with the 9pin.

Simon

[Mr.RC-CAM]

Practical data on a few more LED's has been entered into the "LED roundup" section on the Calculator's web page. I doubt I will review anymore since there is plenty to choose from now.

If you are not sure what is best for you then just buy several different LED's that look favorable and then check them out for yourself. You are the best judge on what will look nice on your nighttime R/C model.

Regards,
Mr. RC-CAM