DIY cheap and easy remote controlled lightning - LED driver

[redbird300]

Well, I decided to start a new thread about this subject, some scale flyers might be interested.

Here is the first post from another thread, and I'll continue the story below this quote:

Originally Posted by redbird300

For those that would be interested in a VERY cheap remote controlled LED driver, which can be switched on/off by means of a TX switch, but also be controlled in brightness by any TX channel if you wish, here's a nice article how to do it yourself:

http://www.zerorc.com/how-build-servo-led-driver

I just build a very dirty and quick prototype, using the circuit board of an old and stripped Towerpro SG90, and tested the device with several channels and switches on a DX7/AR6200 combo, and it works great. Should build a final one now, with several LEDS and in a nice protected and much smaller package, but you get the idea. Enjoy.

Yes, I know, you might find these for a few dollars in some webshop, but this one cost me nothing as I have everything laying around, and it's fun doing it yourself.

I started working on a more final version of a remote controlled LED driver now. It will be used it in a scale project later on.

Below are some pics, look at them first, but come back to read these notes also:

1) The whole thing will be put in a very large piece of shrink wrap (not the LED contacts of course), but I wanted to show the pics before I did that.

2) I used the circuit board of a larger servo this time, a broken Spektrum DS821, to allow for more current, thus more LEDs. Still need to find out how much the circuit will take continuously before it starts heating up, but the LEDs take only 10 mA a piece, so that should allow for a whole lot of LEDs.

3) The black and orange wire that you see in the pic showing the back of the circuit board, are the wires that went to the servo motor. Well, I used thicker wire, but that’s where the motor was connected. They bring + and - V to the two contact strips.

4) The 5 kilo-ohm potmeter from the original servo has been replaced by 2 fixed resistors (2.2 and 4.7 kilo-ohm), look at the left side of the board, you really need a soldering iron with a very fine, needle like tip !

5) The little project has a connector strip at the right side with 2 x 8 connector pins, to allow for 8 LEDs to be separately connected. The normal servo connectors fit, these have the standard 1/10 inch spacing.

6) Last picture: I removed the useless signal wire from the servo connector going to the LED, and did cut the unneeded part of the connector. This will allow the nut and washer around the chrome LED housing to be removed (over the servo connector which is too wide otherwise) when I will need to mount the holder in a fuselage. There are also black plastic holders available.

7) You’ll need a resistor in series with the LED to limit the current, most LEDs take around 10 mA. Some might take a bit more. My resistor is under the black shrink wrap close to the LED, barely noticable. You need to calculate the value of that resistor, depending on the specs of your LED and the output voltage of your BEC. If you would use all the exact same LEDs, you could get away with a single resistor for all LEDs, soldered between the board and the contact strip. Mind the dissipation of the resistor if you do that.

8) Connect the board to any free channel of your RX, and assign a switch to that channel in the TX. No external power supply needed, you’re basically done. Flipping the switch will activate/deactivate the LEDs.

9) You also need to set “travel range” of that channel to maximum, 150% in my case (Spektrum TX/RX), otherwise you won’t get the full voltage from the BEC to the LEDs. This is also a handy way to dim the LEDs, if you would find that they give too much light (with the chosen resistors). An example: with a 5.6 Volt BEC, and travel range at 100%, I got only 3.1 Volts going to the LEDs, but at 150% travel range, this was the full 5.6 Volt. In fact, 3.1 Volts is enough for the LEDs, but I don’t like the idea that I can blow the LEDs up by changing a setting of the TX. So use the full 150% setting, and add resistors as needed, you’ll need to do that anyway in most cases. And it allows for a better spread on the brightness of the LEDs, see below for that.

10) If you have a free proportional channel on your TX/RX, like the AUX3 channel on a DX8/AR8000 combo, you can change the brightness while flying, by turning the AUX3 knob on the TX. Depending on how you connected the two unequal resistors that replace the potmeter, you’ll have control over the LEDs on the low or high half of the channel. The other half won’t change a thing, they will stay in the last position. Not important, but nice to know. Just change the order of the resistors if you regret how it works after having build the project.

11) Use super bright LEDs, you won’t believe how much light these produce nowadays.

12) Dimension are about 5 x 2 centimeter, but as you can see, it could be made a little smaller even, by soldering the resistors straight up, cutting the bottom circuit board, using a separate connector system, etc... Not that important in my particular case, and I preferred mechanical and electrical stability above miniaturization. The weight is 10.2 grams, connector cable included to the RX, but without the LEDs.

In short: I just connect this board to the RX and connect the LEDs to the board.

Tested on the bench in one of my helis, works like a charm. Enjoy.

[redbird300]

BTW, the calculation for the LED resistors is not that complicated, an example:

Assume that you have a 5 Volt BEC, and that you bought a LED that takes 10 mA at 2 Volt, that’s a typical value, but some LEDs are different. These data could be obtained when buying them, or in the data sheet. (If you have an adjustable lab power supply and a multimeter you could also find this out for yourself, by slowly rising the voltage while measuring the current.)

A) Now, in this 5 Volt circuit, we want only 10 mA to flow at most, which will make for full brightness, but no more, that would heat up the LED or even blow it up. Meaning that the circuit should have a TOTAL resistance of 5V/0.01A = 500 ohm.

B) The LED has a theoretical resistance (at 2 Volt) of 2V/0.01A = 200 ohm.

C) Conclusion: you will need a 500-200 = 300 ohm resistor in series with your LED, to make for a total circuit resistance of 500 ohm, being a 10 mA current. Done.

[redbird300]

I made a few more LED wires.

There is one ultra bright white LED, which will be mounted in a searchlight underneath the fuselage later on, a red and a green LED for the left and right side of the fuselage, and 2 orange blinking LEDs for the top and the bottom. BTW, the orange LEDs blink automatically, you can buy them like that, in many colors. All this should make for a realistic imitation of real aircraft lightning. Five LEDs in total, with the possibility of adding three more LEDs.




I connected everything to the AUX2 channel on the AR8000 RX of my (unfinished) heli, and set the channel to be commanded by the “Mix/Hold switch”, in the system setup menu called “Switch select”.

A little demo vid of the LED driver working, flicking the switch a few times:
Don’t pay attention to my little boy talking in the background, lol.

[ame]http://www.youtube.com/watch?v=RQNneizQ24I[/ame]

[sutty]

Excellent Raf. Very interesting, thanks for sharing. That white one is very bright, and I like the auto flashing ones, clever.

Cheers

Sut

[sutty]

BTW, on the first, longest run, I noticed that the flashing lights didn't stay in phase. I guess for obvious reasons, but can they be wired so they would, or stay out of phase? I don't know what real lights do, so not to sure of the importance, but it might be important if you want to have it the same as real ones?

Cheers

Sut

[redbird300]

Originally Posted by sutty

BTW, on the first, longest run, I noticed that the flashing lights didn't stay in phase. I guess for obvious reasons, but can they be wired so they would, or stay out of phase? I don't know what real lights do, so not to sure of the importance, but it might be important if you want to have it the same as real ones?

Cheers

Sut

No, these can't stay in phase. Would be easily possible if you would make a small blinking circuit yourself, and connect the two LEDs to it. The blinking circuit is build in the LEDs in this case, one for each LED, and are independant. Might be a nice idea.

[sutty]

What would happen if they were in series? Would one not turn off the power to the other and re-sync them? Or would that mess with the required voltage. Could two in series have a different resistor to the others? I don't know enough, just asking.

Cheers

Sut

[redbird300]

Originally Posted by sutty

What would happen if they were in series? Would one not turn off the power to the other and re-sync them? Or would that mess with the required voltage. Could two in series have a different resistor to the others? I don't know enough, just asking.

Cheers

Sut

They each need at least 3.5 Volts to work properly, that's more than the normal LEDs, due to the internal blinking circuitry. So there would not be enough voltage available to wire them in series: 2 x 3.5 Volt = 7 Volt, there is only 5.6 Volt available in the circuit.

Even if there would be enough voltage, the internal differences and temperature drift would cause them to go out of synch, if they would start to blink at the exact same moment in the first place.

Best solution is to use two normal, non-blinking LEDs, and connect them in parallel to the same blinking circuit. That would guarantee perfect synch.

BTW, the resistors are already different for each LED, as they are all different types, besides the two orange ones.

[jperkosk]

You could add a blinking circuit to your LED controller board, Raf, I think there is enough space there for that! .

But honestly, what's wrong with them blinking out of synch?

[sutty]

Fair enough, just a thought. I thought they might go open circuit when they went off, and therfore the faster of the two, abeit finitely faster, might govern the rate then. But anyway the volts is the problem then, HV, lol?

[sutty]

Dunno what the problem is Jerry. Might not be, was just asking. Don't even know what real ones do.

[Real_Sparky]

DIY cheap and easy remote controlled lightning

Where do I get it from?
How do I bind to my radio?
This would be very cool at night flys, who needs fireworks

Just dont let in get in the hands of some evil genius


Sorry had to be done

Darin

[redbird300]

Another idea is to connect a small relay, in the same way as the LEDs.

For example like this one, available for a few euros/dollars at many electronic shops:



BTW, you don’t really need the optional blue holder at the right, the relay can be connected or soldered without it also, to keep things more compact.

The two pins at the left are connected exactly like the LEDs (but without resistor), and the 5.6V that will reach these pins, depending on the switch position on your TX, will make the relay contact close. This type of relay needs about 120 mA at 5.6V in the “active” state, which should be no problem at all for the circuit board of a decent servo.

The three pins at the right are the “normally closed” and “normally open”’ contacts. They are able to switch up to 10A/300V. You could for example connect an extra battery, or the positive lead of the main pack of the heli at the middle pin. At that moment, that voltage will be available at one of the two outer pins, depending on the switch position. That way, the circuit is not limited anymore to work only with devices that need 5.6 Volts or less, making for a much broader choice of applications. And you have a lot of electric power available. In a 12S heli, that would be up to 10A at about 50 Volts.

OK, where’s that soldering iron ?

[jperkosk]

Originally Posted by redbird300

The three pins at the right are the “normally closed” and “normally open”’ contacts. They are able to switch up to 10A/300V. You could for example connect an extra battery, or the positive lead of the main pack of the heli at the middle pin. At that moment, that voltage will be available at one of the two outer pins, depending on the switch position. That way, the circuit is not limited anymore to work only with devices that need 5.6 Volts or less, making for a much broader choice of applications. And you have a lot of electric power available. In a 12S heli, that would be up to 10A at about 50 Volts.

OK, where’s that soldering iron ?

Just a word of caution here: switching DC is much harsher on mechanical contacts of a relay than switching AC, as DC sustains the polarity it tends to generate much stronger electrical arc. If you look carefully, the relay in the picture is rated 10A @ 250VAC and 10A @ 180VDC, this is the reason why.

I burnt up many relays in the industrial applications as a young automation engineer by not fully understanding this

Bottom line: to be on a safe side it's a good rule-of-thumb practice to de-rate a relay to 50% of whatever it's rated to when switching DC, improves reliability 10-20 times. In this case I woudn't load it more than 5A. The same limitation doesn't apply to solid state switching devices (such as transistor), as they don't generate a spark on switching.

[redbird300]

+1 Jerry.

I would never go up to 10 A with this one, wise warning indeed.

For those that would be interested AND need such currents, there are larger relays available, that take more current, but will also need a bit more power to switch.

[redbird300]

A large piece of clear shrink wrap around the circuit board, and it's ready for use now.
I'll put a connector housing (without any wires attached) over the contacts that would remain unused, to prevent accidental shortage.

[redbird300]

One more pic, to get a better idea of the size.

[Jonnyheli]

I wish I knew more about electronics and circuit boards etc. I would love to do stuff like that. Those lights are really cool. I'd make so many things if I could. Some days I get the urge to make something but don't have the tools or knowledge to make stuff like that

Jonny

[CyprusDave]

Jonny, the great thing about this forum is that it facilitates the acquisition of knowledge, and it's all free Just act like a sponge and let it all soak in, one day you'll want to make something and you'll remember these little gems, and you'll suddenly realise you know how!

As Jack so aptly said:

Originally Posted by mnwizard

We learn more here by accident, than elsewhere by design

And I've usually found that the stuff you learn by accident if far more interesting and useful than what you (try to) learn by design.

[CyprusDave]

BTY, I don't know if anyone else will agree, but I vote this as sticky material