Remote LED control - for the back of the class
 

We could start with how servos work, pulse width modulation, how diodes work, electron flow theory... but your eyes are going to glaze over, or you'll go back to reading the Rc Car Action that's hidden behind your textbook. Yeah, I saw that.

Pre-requisites:
I have some leds I want to be able to turn on / off from my radio.
I have an extra channel to do it on.
I'm not afraid of a soldering iron.

1 servo
some 2.2k ohm resistors (2,200 ohms)
some resistors somewhere between 150 ohms and 800 ohms

We need a servo to die for this project. Any servo with a good board works even if you stripped the gears, or the potentiometer is bad. nothing to lose trying with a junk servo. My donor this time is a TowerPro SG90, because it's got a tiny board and I got 10 for $18.

I've had good luck before with the PowerHD HD-1900A, towerpro sg90, some traxxas i pulled off a truck. Anyway just try with something you already have scrap.

Start off by ripping the servo open, pull the case screws, seperate everything and pull the board out. The pot can cause disassembly problems if they're screwed in place, or soldered captive. Some like my sg90 had the pot soldered in as an assembly step, so you have to grab some pliers and mangle the case until it lets go.

https://i.imgur.com/MOQfExoh.jpg

Leave the radio pigtail alone.
The pot can be replaced with a y bridge of 2.2k ohm resistors if you feel like it, or you can stay with the Pot for now if it still works.
to make the Y-Bridge remove the Pot, take a 2.2k resistor and solder it to where an outer leg of the pot was, solder the other leg to where center leg was, take another 2.2k resistor and solder where the center leg was, the other leg goes to *the other outer leg* of the pot was. It forms an M that connects where the pot went.
Solder a 150 to 400 ohm resistor to a motor pad or one of the wires that went to the motor,
solder the long leg of the LED to the resistor,
solder the short leg to the opposite motor pad.
Done.

Hook up your new creation to a channel in your rx that gives both throws to a servo, lights should come on in one of the not-center positions.
Tweak the pot to have lights off in center if you didn't make it a y-bridge.
Cool, it works.
Move it to a single throw channel, see if it still works, if not flip the led circuit at the motor pads.


Maybe i want to have one set of lights on, turn them off, and have another set turn on. (switch down - circuit 1, switch center - off, switch up - circuit 2) Wire circuit 1 one direction then circuit 2 opposite at the motor pads as the first circuit.


If you are working at normal RC reciever voltage(7.2v stick pack going into an ESC with a BEC for 4-6v output), a 150 ohm or greater RESITOR will safely get your LED working. Maybe you won't get peak output, but it gets your unknown lights scavanged off something going without freeing the smoke. Also no math.

If you are running red and white leds together like head & tail lights. Make a red circuit and a white circuit. the red need a bit higher resistance or the whites won't work. So my 150 ohm goes on the whites, red gets something 200-400 ohm to start with. play around with values before you finalize anything.
yellows need more power than red, less than white.
blue needs as much power as white (white is usually filtered blue)

If you over power an led, it will light up bright once for under a second, then never again.

try not to string too many leds into a parallel circuit, run a new resistor and wiring for them off the servo. I try to keep it around 10 or less, if you put too many in parallel they can start dimming out toward the end if the wire is high resistance. if you want to run series, it involves some math based on the forward voltage of the led adding together, and the voltage of your input. series lets you go without a resistor sometimes, but series without a resistor can also try really hard to kill batteries if it shorts.

Parallel is what I have mounted in the bumper. anode to anode to anode, cathode to cathode to cathode

https://i.imgur.com/jjnLzwgh.jpg

Series is the row of 3 looking kinda like a WW. Boo this math!

I like micro servos since they break easy everybody has some scrap, are cheap, and someone you know has some broken ones. If you're going crazy with lights, use a bigger servo board since they work with more power. If you're going absolutely insane with lights, maybe that battle switch or a cheap esc is the way to go.


If you have LEDs or other components that have a long leg and short leg, the long one is + Positive. It's easy to remember that if you trimmed the legs even, it gives you a small piece that can lay over that leg so it looks like a + and the short leg doesn't have one so its still a -

the other way to tell polarity of a Light Emitting Diode is hold it up to a light, one leg goes to a big triangle, the other has a weird shape. big triangle is - negative.

Re: Remote LED control - for the back of the class
 

The servo listed in this tutorial is good, the salvaged resistors i was using weren't.

It doesn't have to be pretty or fancy, this one is kinda spread out to look pretty and show individual parts. My wiring is a bench test of unsecured spaghetti because it doesn't matter for this pic. Just look at the board, It's the same as the single led in the first post. I like to color code (like shown) but it doesn't matter if you don't.

https://i.imgur.com/9WGGwXeh.jpg

I've got the 2 resistors in the V shape replacing the potientiometer, their other ends go to the outer leg pads. I used 2.2k ohms here. That's 2,200 ohms. Exact value on these isn't as important as having them the same value. This makes the servo think it's centered, so it could be used on a 3 pos switched channel to run 2 circuits at different times. If you use a light that's not an led, you'd have to use a Diode to turn it off at the wrong polarity since they don't care about polarity, they work either way.

The 3 resistors hanging off the side of the board are current limiters for each color in my circuits. Resistor sits on the old motor hookup pad, the other wire comisg back off the circuit ties to the other motor pad.

My example is a servo board running 2 headlight, 2 yellow markers, 2 red markers, and 6 taillights. These are basically run as 3 parallel circuits, one for each color, and they all tie in at the motor pads on servo board.

To run Red leds, you're usually going to want around 470 ohms.

To run Yellow or Green leds, you're usually going to want around 220 ohms.

To run White or Blue or Purple, you're wanting something more like 110 ohm.

These values aren't exact. Or anywhere close to optimized for your leds. This is just an easy way to get lights without caring about forward voltage, current drop, and any math. There is no tracking down datasheets for parts you don't have a build company or part numbers for.

Yellow takes more power than red, if you matched their resistors only red would light.
White takes more power than yellow.
Blue, white, and purple are all filtered blue
Green is filtered yellow.

If you use a higher value resistor, light get's dimmer.
If you put a lower value resistor on, light gets brighter.
If you put a much lower value resistor on, light goes flash and never works again.

If you want the light to turn on/off slower more like a halogen or incandescent light, you can put a CAPACITOR across the motor pads where your lights attach. Also if your lights are kinda strobing, a cap can help smooth out the pulse width modulation. Don't use an eletrolitic cap that's polarity sensitive, just use the cheap ceramic disc caps like we used on motors.

How do you eat an elephant? One bite at a time.
Complex circuits can get overwhelming, so just think about 1 wire or led at a time.

Go put some lights on something, it's not that tough. Show us your lighted stuff.

Re: Remote LED control - for the back of the class
 

Cool! Thx for posting.

Re: Remote LED control - for the back of the class
 

I should have mentioned you'll probably want to insulate the electronics with something like heatshrink, tape, hotglue, a bag, plastic box...

If you put the Hacked Servo light circuit on a Stick or Potentiometer channel on your radio, it will let you have dimming through the radios Pulse Width Modulation. Maybe you want dimmable interior lights, or underglow, or something.

If you're running a more complex circuit that has a timer chip or something, you'll need to step up to a Recciever Switch instead of just a hacked servo. Most servos aren't going to drive the Output close enough to 100% duty cycle to ever let it run, so it'll constantly be resetting many times a second. You *could* make a transistor H-bridge setup still using the servo board to trigger on/off, but if you wanted to do that ya wouldn't be sitting in the back of the class with me.

An example, I built a Wig-Wag using a 555 timer chip circuit, which alternates 2 light circuits. It fails miserably hooked up on the Hacke Servo, but works perfect on a Recciever Switch. These switches generally add 2 or more "channels" of control (even though only using 1 actual radio channel) that are accessed by sequences of + and - throws from the radio, and really go beyond our scope of let's mangle some trash to make something cool. Plus they're pretty cheap too.

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Those nerds way up at the front of the class are doing some pretty cool stuff that can usually be adapted to our needs.
https://os.mbed.com/users/4180_1/not...-for-modelers/

Some sellers of interesting effects i've run across, but I have not done business with and can not vouch for.
https://www.modeltrainsoftware.com Evan designs

https://www.miniatronics.com/Merchan...ategory_Code=2 Miniatronics

http://www.bakatronics.com/shop/category.aspx?catid=133 Bakatronics

https://tennentm.wixsite.com/ironpenguin Iron penguin

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Questions are welcomed, if you try any of this i'd love to know and see pictures!

Re: Remote LED control - for the back of the class
 

Receiver Switch with 2 pigtails seems like it would be ideal for blinkers at least, tapped into the steering servo. Servo tap for the Brake-lights and reverse lights, and probably a third channel to control the on-off-high lighting. (Add a 4th channel with a switch to control Hazards maybe?)

Re: Remote LED control - for the back of the class
 

Probably could do that, if you had a set of blinking leds that didn't care about not getting the full duty cycle, or could use caps to smooth out the pwm into something stable enough. Or throwing a transistor and some other stuff on there that can latch it on above a certain threshold. But that's getting more middle or front of the class, not joking around and reading magazines back here.

Reverse lights are easy enough if you just tap the motor leads and set polarity correctly.

At that point if there's room, a dedicated drop-in light controller circuit would be easier. I'm running some that were under $15 that can output for marker lights, running, turnsignal, brake, reverse, headlights (either On or toy-style On / switching Highbeam above certain throttle.) It just pigtails 2 channels between RX and servo and drive esc.

Hazard lights would be sweet, i just haven't found a cheap one that does it yet.

Re: Remote LED control - for the back of the class
 

I'm actually looking at making my own hazard light controller out of a 555 timer and some resistors dead-bugged and soaked in plastidip.