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Remote controlled helicopters and other toys have become incredibly advanced for a very low price, this is partially thanks to the huge mobile device market, which has pushed technology in small high energy batteries forward and ramped up production of micro motors. A stable micro helicopter which can fly for 5 minutes on a charge can now be gotten for $20 or less, and there are many interesting variants like UFOs and mini quadrocopters.

   The main downside of these devices is that they use infrared (IR) remote control rather than radio, this is the same technology used in television remote controls. It works by pulsing an IR LED light, which is invisible to the human eye, and the device being controlled detects the pulses using an IR phototransistor, which changes its resistance when hit with IR light. Because these devices are light dependent, they require a clear line of sight between the transmitting LED and the receiver. Since this is a flying device, if anything, even the body of the helicopter, blocks the path for a moment, it crashes to the ground. It is also very susceptible to interference. Sunlight is full of IR light, which means the helicopters cannot be flown outdoors.

   Radio control on the other hand works in any light and does not need a clear line of sight. The power consumption and weight do bring the flight time down a bit, from 5 minutes to 4 in my case, but I am able to fly for the full 4 minutes without any loss of signal, and from very far away, 50 to 100 ft, and outdoors if it’s not too windy.

This is my method for making a Syma S107 helicopter work by radio using an ASK transmitter/receiver set, that are sold commonly on Amazon, Ebay and many other sites for around $5, typically in 433 MHz, or 315 MHz.

If you like this, vote for me in the Hardware Hacking Contest.

This video is a little "walkaround" of the modded helicopter:


Here is a video of it flying. It was hard to get clear video of it. This could qualify as one of those blurry UFO videos, blinking lights in the sky and all:



Step 1: Getting the Parts

Resistors
For this I used common through hole resistors. 1k and 10k. You can vary from that a bit if you have something else on hand.

Transistors
If you are ordering one just for this, go with the 293904.

Pretty much any NPN signal transistor will work, and the package type (the style of case it is built into) is TO-92. The particular one I used was a BF420, but that's just what I had in my drawer, any of the following should work.

2N3904
BC337-25
BC337-40
BC547B
BC547C
BF420
PN2222A
STPSA42

Receivers that will work

Make sure you pick a receiver that can operate at the voltage of your helicopter's battery. Most of these batteries are 3.7V lithium polymer. They reliably put out a bit less than that (3.4V or so). and the majority of these receivers are 5V. Sometimes you can get away with under powering a device, but with these receivers I haven't found that to be the case.

This one from amazon lists the voltage as 2.5-5V for $5 free shipping
T
his is a set, but you could use the transmitter with the above, and you have a spare, it's $1.20 free shipping

Depending on what you find, I might order a few different ones to try and test it on a breadboard.

Step 2: Modifying the Transmitter

The main trick to modifying the transmitter is finding the connection points. There are lots of notes in the pictures below, so be sure to take a look.

Ground Plane
  • Follow the black battery lead on the front, you should be able to tap into where it comes out on the back
  • The ground plane is usually the big plane that fills most of the board
Supply
  • Like the ground, look for where the red lead comes in.
Signal Output
Here's the tricky one. You don't want to take this off of the trace connected directly to the diode. Look at the pins from the chip on the front. One of them will have a path to the IR LED transmitters at the top of the remote. Probably going through a tiny capacitor and a transistor. (See picture for more notes on this). If you have the exact same controller I do, it's the pin in the upper right when looking at the back of the controller.

Antenna
For this I used a piece of solid hook up wire because it's stiff. Some thick magnet wire would work well too. For best results the length should resonate with the frequency of the signal. You can find the equations for this on wikipedia, but I just used the website in the picture below. For 433 MHz, the 1/4 length is 6.48 inches.

Modification

Once you've found all these it's a matter of connecting the transmitter to them. I think it's best to attach the wires to the transmitter unit first, then attach the ends to the points in the controller. If your transmitter has legs you can just spread them out, spiral wrap around them and solder on, then put some electrical tape between them for good measure, see the next page for more on the lead wrapping technique. If it has holes, like mine did, just twist the stripped wire ends, poke them through and solder. Don't make the bare wire too long, you don't want it shorting against anything.

On the controller side of things It helps if you heavily tin the wires with a big bead of solder first. If you have a point where a lead comes through, solder to that. If not, use a razor knife or a file to clean off some of the green masking and tin it with solder, then attach your wire there.

The positive voltage on the controller PCB goes to VDD on the transmitter module, it may be labeled VDD, +V, +5V, POW depending on model

Ground may be labeled GND, -V, VCC, or the ground symbol, which looks like an upside-down antenna

The signal input may say DATA, or INPUT. If there is one labeled TE it's not that.

Step 3: Adding a NOT Gate Signal Conditioner to the Receiver

This step is all explanation, you can jump ahead if you just want to build it.

Logic Inversion
It is necessary to invert the logic on the receiver. This is because the IR receiver was designed to use a photo-diode, which blocks current when it is struck by enough IR light. So the chain is:

With IR transmission
  • Transmitter output signal voltage goes high
  • Transmitter IR LED emits light
  • Receiver Photo transitor impedance goes high
  • Voltage through photo diode into controller board goes low
With Radio Transmission
  • Transmitter output signal voltage goes high
  • Transmitter radio signal goes high
  • Receiver output goes high
  • Voltage through from radio receiver into goes high
Amplification

It also helps to amp up the signal a bit coming from the receiver.

How?
Don't worry, this can all be done with one transistor and two resistors. We have to keep it simple and light after all, the helicopter will be carrying it.

A NOT gate is nothing more than a switch which turns off when it receives a high signal and on when it receives a low signal. Configured as a very simple inverting amplifier an NPN (negative positive negative) transistor will do just this.

Step 4: Building the Signal Conditioner for the Receiver

The first image below is the whole circuit. To make it compact were going to put the resistors in line with the legs of the transistor and lay it down against the board.

Figuring out the legs (E, B, C)
First, make sure you identify your transistors legs by looking up the appropriate data sheet. It should give you the Collector, Base and Emitter relative to the flat side of the transistor. I think on most of the ones I listed if you hold it with the flat side facing you, the left to right order is E,B,C. For example here's the datasheet for the 2N3904. If you got a different one, a internet search for the part number + datatsheet should come up with what you need.

Construction

(first picture of build) I like to do a spiral wrap for these connections, it's easiest with the cheap resistors which have really thin legs. Once that's done it will stay in place and you can solder it up.
(picture 2) The device with all the wires and resistors attached in a similar manner.
(picture 3) Put some shrink tube on the middle if you've got it, otherwise use some electrical tape. Leave the leads long, we'll customize the length on install.

Step 5: Installing the Modded Receiver

The first picture is of my original build. I laid the conditioner down on the board, and cut the leads to length so they would match up cleanly. Remember to add wires to go to your helicopters control board. I find it easiest to just twist both together and put them through the hole, then solder both.

You need to be gentle with the top of your helicopter when you pull it off to get to the board, there are some very tiny wires there. Luckily none of mine have broken any time I've done this. You'll need to swing the main board aside and desolder the IR phototransistor. If you have desoldering tools this should be easy, otherwise, clip it off, take some small pliers, and grab the remaining pin bits one at a time, heating the solder holding them and extracting them. 

(middle picture) After that you'll want to feed the wires from your receiver through the hole that the IR phototransistor used to pass through, and like the receiver, twist and thread the stripped ends through the hole. Be careful not to over solder onto the adjacent pins.

The next picture shows it all assembled. Put it all back together with the radio receiver hanging out of the back, then fold it over so it sits under the belly of the helicopter. I taped mine into place, but maybe a zip tie would be better.

Have Fun

As with any hack, this might take some tweaking and retrying depending on what you have. I'll be watching and answering questions on this over the next few weeks. If you liked it please vote for me in the Hardware Hacking Contest.
Hey there, im wondering, can i bind my 107p transmitter into my s107 heli?
<p>What can I do If I lost transmitter from my heli?</p>
<p>Hello Paul, just purchased a ir heli (Not the S107) for my daughter and need to convert it to RF, I've purchased the hardware you've stated but before going ahead, I would like to confirm a couple things with you, that even if the tx has a switch for multiple ir channels that this mod should still work?<br>The attached pic shows an orange line following the track to what I believe the output on the IC is, I know you can not be 100% without testing, but it matches your description.</p><p>Thank you<br>Cheers </p><p>Rob </p>
<p>Sorry to reply to my own comment but can edit!</p><p>The receiver isn't marked and the ir diode is the round 3 leg type, middle is ground, leg with the flat is Cathode correct, would that be output?</p><p>Thanks again mate</p><p>Rob </p>
<p>If you give the heli power you should be able to check with a multimeter which pins get power, that will tell you + and -, the remaining one is signal. As you see here it varies: <a href="https://arduino-info.wikispaces.com/file/view/IR-Receivers-900.jpg/473330184/800x225/IR-Receivers-900.jpg">https://arduino-info.wikispaces.com/file/view/IR-R...</a></p><p>From the look of the board I'd say you've got the signal leg on your controller right, it goes through a resistor and to a transistor base pin in the exact same way.</p>
<p>Thanks for you help mate really appreciate it, love your tutorial!!<br>Made a test rig to ID the IR sensor pinouts, so that's all good now too!<br>Again thank you!<br></p><p>Cheers<br>Rob</p>
<p>The Screws r so small... gonna chk if i even have a screwdriver of that size..</p>
<p>I didn't see this until the other reply. Yes, I think with a normal set of miniature screwdrivers you should be able to get them. If that's hard to obtain in your area a drugstore might have a glasses repair kit, which are usually cheap and come with a small screwdriver.</p>
<p>dont be fooled.Those screw r not that small its a common size screw.If you don't have a screw that size use army knives or scissors </p>
<p>dont be fooled.Those screw r not that small its a common size screw.If you don't have a screw that size use army knives or scissors </p>
<p>Interesting. I was looking into adding a BMP085 motor temperature/ altitude limit and brown out detection on my S107 as one annoying habit is for it to lose power in the middle of a flight; this happens because the chip accumulates more noise at lower power levels causing it to spectactularly crash at around +3.4V Vcc if the failsafe on the pack doesent do it in first.</p>
<p>Hi, I would like to use the Helicopter transmitter as a input to a Arduino with a IR receiver. Has anyone done this?</p>
<p>There is a project where someone reverse engineered the protocol to make an arduino <em>send </em>the IR signal. It was on RC groups I believe. That may be a good starting point. If you just want a remote control for an arduino project I might suggest one of the ready made bluetooth arduino remote projects, the chips are very inexpensive (look for arduino bluetooth module) and there are many projects that already support it. xBees have a good library of projects too, but they cost a bit more.</p>
<p>Hi Paul,</p><p>I understand you connected the antenna directly on the chip pin that used to drive the transistor in serie with the IR LEDs.</p><p>Why choosing to do so ? One could say the transistor would handle better the load of the antenna rather than the chip pin. Nobody knows what kind of max current this pin is rated for. Especially if there are several versions of the controller chip.</p><p>Have you tried to tie the antenna directly to the LEDs high side ? I think i'm going to try this, as it implies less work with the desoldering / soldering.</p><p>From my POV, the parts that link the LED and the controller chip are a transistor and resistors (2 of theme). You mentionned a capacitor. I can be wrong but i'd be surprised to see a capacitor there.</p>
<p>I did try the part that the LEDs connect to, and for some reason it didn't work. Connecting the receiver to my O-scope I didn't see any signal. I don't know if the signal was at the wrong level, if connecting that size of load to the transistor was too low and shorted it, or too high and drained it, or something else. I also tried all four combinations between tapping the signal off of the chip or after the transistor, and inverting the receiver signal, or leaving it non-inverted. This was the only one that worked, but with more investigation I'm sure other ways could work too. I realized after doing this project that the inverter could very possibly have just made this work because it also boosted the signal, and that if a non-inverting amplifier were attached the signal could be inverted on the sending side, which could possibly be done just by tapping it in a different place. There are probably a lot of ways this could be done. If your experiment works please let me know the results. I'm an automation engineer and only have intermediate knowledge of radio signals, and I knew even less when I did this project.</p>
Hey, just wondering how long it would take you to do all the steps from start to finish? Also approximately how much would be the cost of the modifications? Doing an assignment and need such info's. Thanks.
Hey, just wondering how long it would take you to do all the steps from start to finish? Also approximately how much would be the cost of the modifications? Doing an assignment and need such info's. Thanks.
Great Instructable. I have a pile of old IR copters and receivers. I will now be able to breathe new life into them!
Cool, I'd like to hear about how it goes and if you figure out any new tricks in the process.
Great project. Very useful Instructable. <br>Some questions out of interest: Is using 433 MHz or 315 MHz for models legal in the States? <br>In Belgium it isn't if you take it to the letter (although probably nobody will notice as long as it is a legal frequency for &quot;home&quot; applications). <br>Also, do I understand that using the Tx/Rx as such you will not be able to use more than one pair in the 433 MHz? There is no narrower band (crystal or synthesized), nor any identifying code (as in 2.4GHz systems). <br>
Good question. I think they are legal in the US, this is a band unregulated and is often used for remote control lights, keyless entry systems ect. <br> <br>The use of multiple ones at once depends on the helicopter. Syma 107g helicopters support 3 channels labeled A, B and C. The ID coding is in the data, not the carrier frequency. I have been able to run two at once with both being 433 MHz, one set to A and one to C. I have never tried more, but would speculate that you could use one on each code supported by your device, on each frequency, and that 2.4GHz would probably work. So if you use 3 315 MHz, and 3 433 MHz, you could probably fly 6 at once. But I can't guarantee it, because there may be interference. Your best bet to be sure if you just want to run 2 is probably two different carrier frequencies. <br> <br>As with all stuff I've posted here, since this is a hack I suggest getting a few different parts to try. There are so many variables. And you can always use the spares for other stuff.
hey, I have apptoyz appcopter, and my controller (this part that i connect to iphone or android device) is broken... is there any way to control this heli instead of using original controller?
Did you mean do away with using the phone and using a 'standard' helicopter remote? I am no electronics wiz but I suppose if you get an old IR remote from an auction site, then carry out the mods as above it should work.
I'm sure there is some way, I'm not sure how hard it would be. How did the old transmitter connect to your phone? Does it look like the helicopter as an IR receive or an antenna?
heli has ir receiver on the bottom, transmitter connects with phone using 3,5 mm jack , transmitter stopped working some time ago, i would like to know if there is any possibility of control without using original transmitter <br>
Ah, that narrows things down a bit. The old device was probably just using the sound output to drive an IR LED. If you want to restore the IR capability, you could probably make your own with a headphone jack and two IR LEDs. <a href="http://www.rtfms.com/wp-content/rtfms-com/bill-of-materials-iphone-remote-580x435.png" rel="nofollow">H</a><a href="http://rtfms.com/episode-4-turn-your-iphoneandroid-mac-pc-player-etc-into-a-universal-remote.htm" rel="nofollow">ere's a tutorial I found on how to make one (not my work)</a>.<br> <br> If you want to use my tutorial to do it you would have to wire the audio output into the transmitter. It would need separate power leads. My best guess is that if you got a mono jack, tapped connected ground on the transmitter to the sleeve, data to the center, and the supply to a 5V output on your phones data port it might work. But I haven't tried this so I'm not sure.
If anyone is buying the parts just for this, here is a list to get what you need from tayda. They work well for small parts orders, the parts are only going to cost you 8 cents, but the order will be about $6 because there is a $5 minimum and $1-$2 shipping.<br> <br> <a href="http://www.taydaelectronics.com/2sc2240-npn-small-signal-transistor.html" rel="nofollow">2SC2240 NPN SMALL SIGNAL TRANSISTOR - $0.06</a><br> <a href="http://www.taydaelectronics.com/test-group-43.html" rel="nofollow">Through hole resistors, get a 10k and a 1k- - $0.01 each</a><br> If you want to make use of the minimum and are new to electronics, here's a few parts you might want to throw in:<br> <a href="http://www.taydaelectronics.com/l293-l293d-push-pull-4-channel-driver-ic.html" rel="nofollow">L293 push pull 4-challen driver, Lets you run small motors both ways, or drive a stepper with a microcontroller</a><br> <a href="http://www.taydaelectronics.com/lm7805-l7805-7805-voltage-regulator-ic-5v-1-5a.html" rel="nofollow">A big mosfet - run a motor in one direction or blink a light</a><br> <a href="http://www.taydaelectronics.com/ne555-ic-555-timer-dip-8.html" rel="nofollow">A 555 timer - tons of project use these, they let you create a regular pulse, so you can buzz a speaker, run a pwm servo ect.</a><br> Other than that maybe some resistor and capacitor assortments<br> <br> If you live near a radioshack, they have transistors, they cost 30 times as much, but there's no shipping:<br> <a href="http://www.radioshack.com/product/index.jsp?productId=2062609" rel="nofollow">Transistor $1.49</a><br> <br>

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Bio: I am a robotic engineer, and I like to make things and teach others.
More by PaulMakesThings:Add Radio to a Syma S107 IR Helicopter (or any other IR device) A 3D Print Ready Jack O' Lantern in Solidworks 3D Printed Hanging Internal Gear Clock 
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