How To: Circuit Hijacking
Several projects on this site involve the modding of consumer electronics for new and inventive purposes. The NES tv remote for example used an old remote control as the base of the whole project. However, the circuitry inside was diverted to the controls of an old NES controller. This process of redirecting the internal circuitry of a component is what I call “circuit hijacking” because essentially, the circuitry is “hijacked” to a new location and purpose. This method is by no means new, nor is it even difficult but in this article I will attempt to described the best ways that circuit hijacking is accomplished so you can begin hijacking your own circuits. Note: This is meant as an introduction to circuit modding. The elements covered in this article describe very basic techniques as this guide was written for the beginner. However, hopefully the tips recorded here will be of value to all.
1. The first step I take whenever I attempt a project like this is to spend some time analyzing the component’s original circuitry. You should look at the circuit traces and try to follow the logic to see where and how the component actually works. You don’t have to understand all of the circuitry but it definitely helps to understand the portions of the device that you want to alter. In reference to my remote project, I studied the lines that ran to channel buttons and volume buttons. These were the buttons that I was re-routing to connect with the NES controller’s buttons.
Above you can see what typical button connections look like on most circuitry. This means that below those rubber buttons of a remote control are circuit traces that look like this. When the rubber button is pressed a connection is made between the two segments of this connection and the desired function (channel up, for example) is activated. In my plan for the NES tv remote, I had to hijack the function of these buttons and re-route them to similar buttons from the NES controller circuitry. Thus, whenever the buttons on the NES controller were pressed, the corresponding functions were activated on the remote control.
2. The next step in hijacking the circuits is to scratch off a small portion the trace material covering the circuit lines. These lines can be of several colors but in the picture above, I am referring to the light green lines. Below this trace material lies the actuall copper (orange in color) used for conducting the current. This scratching is necessary as solder will only stick to the copper underneath. If you try to solder to the trace material the solder will simply ball up and fall off. In addition to scratching off the trace material on the hijacked board, you will also need to scratch off the material covering the copper lines on the board that you are re-routing to if necessary. For example, to hijack the circuit from my remote I scratched off a small portion of trace from the channel and volume button pads in the manner shown below.
3. Next you will need to solder wires to the scratched off portions of your circuit board. So, in my example above, I soldered one end of a wire to each of the exposed points of copper. Remember that solder will only bond with the copper portion of the board, but you will still need to be careful not to touch other components nearby. It is possible to damage IC’s and other components with too much heat. You will need to make sure that you have a good bead of solder on the connection with your wire to make sure that it will be stable and will conduct properly. This will need to be done for each button you are attempting to hijack.
4. Lastly, you will need to solder the ends of the wires you previously soldered to the original board to their new button pads. The new layout should be similar to the diagram above. When the button for the NES controller is pressed, then the circuit is closed for the remote’s button which activates the desired function (i.e. Channel Up). Once this type of connection has been completed for every button you wish to hijack, you are finished. Further details about the rest of the NES TV remote project can be found here.
Hopefully, this guide helped some of you understand the principles of circuit hijacking a little better. But, as always, if you have any questions feel free to leave them in the comments below or send me an email.
Really interesting, but too short… I wanted to learn electronics for a long time, but never found anything targeted at beginners like this. Could you please write some more articles like this one? That’d be great!
thanks Eric. And that’s a good idea. I really like working with electronics so I’ll def. post more howto’s/articles in the future.
this has got to be the worst tutorial ever. sorry, it introduces excrutiatingly intuitive concepts and lacks depth and direction.
quit your bitching man thats lame of you to bag on this guy. Do better yourself first, THEN you can make fun of those below you.
“excrutiatingly intuitive concepts” …do you even know what those words mean? a 10 year old could follow this guide. nice tutorial man
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It’s short but a good start, would definetly like to see more. Good tut man.
Sometimes you need to break etches to make things work. A good SHARP knife is a necessity here. My favorite for this purpose is a GrifHold stencil knife. It will dull quickly in this use, even if the traces you’re cutting are on paper/phenolic circuit-board (glass/epoxy is the worst), so buy a sharpening stone and some oil to sharpen it back up; you can reuse it until it’s sharpened down to the nub. This blade is a better tool for scraping off solder-mask (the green stuff covering the copper traces) than just about anything. Xacto blades are mostly too thin and flexible to be effective trace-cutters (a diagonal chisel blade in an Xacto #5 handle is decently thick but hard to maneuver in tight places).
For breaking etches, separate your forces: the hand holding the blade bears down, while the thumb of the other hand pushes it into the copper.
A one-handed method doesn’t give you enough control, and frequently causes the blade to skid and cut into adjacent traces.
Cut two incisions ‘facing each other’, perhaps a millimeter apart, then pick away at and lift the copper between them. Don’t pull up the whole trace; you might need isolated segments of it later for patching in discrete components.
For patch-soldering to traces, use a good temperature-controlled iron with an 800-degree tip — you want to get in and get out quickly, before your soldering heat can spread enough to decay the adhesive holding the trace to the board, resulting in a lifted trace or pad, and that means higher localized heat. This will also minimize your chances of melting the insulation on your patch wire (I assume you’re using AWG#30 wrap-wire, with Kynar insulation) and causing a short-circuit.
If you’re going to do a lot of prototyping and patch-wiring like this, AWG#30 Teflon-insulated wire is a good investment: the insulation stands up to soldering heat much better than Kynar or PVC. So is a spool of 63/37 “eutectic” flux-core solder, if you can stil find it (lately the industry has been phasing out lead-bearing solder; as with any lead-bearing material, wash hands after handling it before eating, drinking or smoking).
I need to clarify one remark in the above: the solder to use in electronics is RESIN-core, not acid-core (’flux’ describes either). As long as I’m adding this: the solders I find most useful for this kind of work are .037″ and .020″ diameter, both of them Kester “44″ brand solders (are they still in business? My spools are a couple of decades old).
it 2006!!!!!
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I think that the traces on the PCB are not “closed” by the button press, but they form a parallel plate capacitor. It is part of a tuned circuit that increases in capacitance when the dielectric piece under the button moves near the traces.
Some are capacitive, James, but others (Shin-Etsu is a brand that comes to mind for the buttons themselves) have a resistive surface cooked onto the bottom of the ’squishy-button’, and they do make direct contact with the naked copper, shorting the contacts together. Have a look at the bottom of the button itself — if it’s got a black carbonlike coating, your DMM will probably read a low (>1K) resistance (but not quite zero-ohms) when you (gently) jab it with the probes. This is what’s designed into all the infrared TV/VCR remotes I’ve opened: silicone-rubber deformable buttons with carbon-black contact surfaces baked onto the bottoms, designed to short together fingered contacts like those depicted in the above article.
In some cases, the hacked-in circuit will work with the original circuitry left intact, in parallel. If it acts flaky, or flat-out doesn’t work, though, you might need to break the traces leading to the (unpowered) original circuitry to get their loading out of the circuit. Check the button-open and button-closed voltages, comparing them to the voltages at the battery terminals (better yet, ’scope the connection, if you’ve got a ’scope, and look at the RC-discharge curves through the button’s contact-material), to see if such leakage is interfering… Or just go ahead and cut the traces, if you’re sure you won’t use these things for their original purposes anymore.
crb3, thanks for all of the usefull info. your comments are probably more helpfull to most than my article. I hope you will stick around zerosign.net and continue to contribute quality information.
Nice tutorial. For correctness, here is a quick terminology fix. What you refer to as “traces” and “trace material” is actually called a “solder mask”. The trace is the signal line of made of copper. I was confused a bit when you suggested scratching off the “trace material” since this would break the circuit!
Here is a definition of solder mask found by googling “define: solder mask”
Solder Mask
a coating on a PC board, usually a dark green or dark blue, but occasionally a yellowish color, which is designed to insulate and protect the copper traces and keep them from shorting together during the wave soldering process. The soldermask is “masked out” at solder pads, to allow for soldering component leads.
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There’s an excellent tutorial on basic hobbyist-level soldering and circuit assembly by Edwin Olson, an MIT instructor, on the OrcBoard site:
Soldering Tutorial (PDF), written by Edwin Olson (eolson@mit.edu). A guide to soldering thru-hole and surface mount parts at home, using ordinary soldering tools.
The first few pages are pitched to engineers, so they’re heavy on the “what”. If that makes your eyes glaze over, skim through that to the tool-list and the pictures, where he lays out the “how”, and come back to that “what” text later when you want some “why”.
Look carefully at his pictures of the actual soldering. The flux core in the center of the solder wire will ’spit’ molten flux out when it’s heated, and that
spat-out flux should be aimed (as precisely as you can get it) at the junction of the components (component-lead and PCB pad, or stripped wire tip and connector pin), because that’s where the solder needs to flow into.
In the step-by-step pictorial for soldering cable wires to connectors, there’s a step (taught to me by a NASA instructor) that he didn’t mention. Strip bare a little more of the wire tip than you need (figure this into your lengths). When you ‘tin’ the wires (fill the cluster of thin solid wires which is the stranded wire up with solder, binding those small wires together and wetting their surfaces with solder in preparation for soldering to the connector), end your iron contact with a stroke towards the tip. The excess solder will blob there. Using diagonal cutters (or, better, flush-cutters like MicroShears), clip that tinned tip down to the working-length, thus clipping off that bulb of solder. That leaves the tinned wire-tip more managable, whether you will then bend it around a post, hook it through an eye-loop, or stick it into a solder-cup.
About the only parts I disagree with are things I’ve already mentioned here: never use acid flux or acid-core solder on electronics (because the acid will keep on attacking the copper as long as it’s left in place); and use an 800-degree tip on your iron so you can get in and out quickly. Olson recommends a 600-to-700-degree tip, but I’ve seen too many circuit boards messed up (lifted pads, heat-zapped components),so that’s what most production assemblers used in places I’ve worked) or filled with cold solder joints, by production assemblers who use those low-temp tips and then have to hold the iron to the board entirely too long to get the junction-to-be-soldered up to temperature.
excellent material very helpful for some projects that i am goin to start
Thanks
ez
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For safely removing SMD’s from the circuit board, try the
Chip Quik SMD removal kit. All you need is a solder iron &
a pack of Chip Quik. Try it
www.chipquik.com
Also read the rework newsletters on the site.
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OMG, im new to circut hijacking, hacking of all sorts(even though this sint hacking), i am completeley excited to say, i comeplteey understand the NES+TV remote guide, its really understandable and its not complicated in the least. TY
Very interesting and idea generating how to. Thanks for writing these tips.
I took apart one of my gizmos recently (pocket pc) and tinkered with it a bit and was nearly impossible to get it closed up again. Never quite worked the same though
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Great post. I’ll think about that.
thanks for a nice post such as this.
much apreciated keep up the good work
keep going
this is cool
great post easily to read and understand and a great layout well done
Great post will think about your comments for my next project
great post well done
credit were its due
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Hey - I have tried this on an old sega joystick with great results - it now plays Mario sound fx from a keychain i got from thinkgeek! the arcade style, six button set up matches up with the 6 sounds on the keychain. I am pretty sure sega never had mario games but that is beside the point… I really wanted to point out that there is no wiki entry for “circuit hijacking”. just thought id throw that out there for you in case you have the time to start an entry!
E
It all makes perfect sense now. Cheers for explaining things in layman’s terms
Im still abit confused. Not sure about what when im trying to replace the old one with a new one, :S
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