[Rostislav Persion] has for some time been interested in making small, portable EMP devices capable of interfering with nearby electronics. In these EMP devices, high voltage is used to create a portable spark gap generator, whose operation in turn creates electromagnetic pulses capable of resetting or scrambling nearby electronics such as pocket calculators.
His original EMP box designs relied on spark gaps constructed from metal screws threaded into a clear plastic insulator, but this newest design ditches fussy screw adjustments and relies on perfboard. By cutting out a single row of plated perfboard holes and soldering the high voltage terminals to each end, the empty holes in between form the essential parts of a spark gap.
It’s even adjustable: one simply bridges adjacent holes with solder to effectively decrease the gap. As for generating the high voltage itself, a DC voltage multiplier from Amazon takes care of that. Watch the device reset some calculators in the short video below.
When it comes to high-speed, high-voltage switching, there are a wealth of components to choose from — MOSFETS, thyristors, IGBTs, and even vacuum tubes like thyratrons. But who needs all that expensive silicon (or glass) when all you need to build a high-voltage switch is some plumbing fixtures and a lathe?
At least that’s the approach that budget-minded laser experimenter [Les Wright] took with his latest triggered spark gap build. We’ve been watching his work for a while now, especially his transversely excited atmospheric (TEA) lasers. These are conceptually simple lasers that seem easy to build, at least compared to other lasers. But they do require a rapid pulse of high voltage across their long parallel electrodes to lase, and controlling the pulse is where this triggered spark gap shines.
The spark gap is made from brass plumbing fittings on either end of a short PVC coupler. [Les] used his lathe to put a thread into one of the caps to accept a spark plug, the center electrode of which pokes through a small hole in the metal cathode. To trigger the spark gap, [Les] built a trigger generator that outputs about 15,000 volts, which arcs from the spark plug electrode to the spark gap cathode in the low-pressure nitrogen environment. Little spark leads to big spark, big spark discharges a capacitor across the laser electrodes, and you’ve got a controlled single-shot laser. Check it out in the video below.
This project shows a simple and well polished implementation of a differential-to-single-ended preamplifier, which allows a differential signal to be probed and fed to an oscilloscope via a BNC cable.
It implements a classic instrumentation amplifier, where we have two amplifier stages. The first gives us the options for a gain of either 1 or 10, if we need it, with the second stage having a gain of 2.
The remaining circuit is a power supply to generate the necessary dual-rail supplies to feed the opamps. There is a lot of filtering on those output rails as well as on the USB power input side to try keep all that switched-mode power supply noise out of the signal path.
There are a couple of interesting design choices including the use of PCB material for the long removable probe arms, that integrate PCB spark gaps to offer a first defence against ESD reaching the more delicate parts of the system.
Why This Is Useful
There are two main classes of signals we electronics engineers care about: single-ended and differential-mode.
With the first kind, the signal is carried on a single wire, which is defined as being referenced to the common system ground. Current flows along the wire and returns to its source along the path of least resistance, at least at low frequencies. At higher frequencies, the path of least inductance is more relevant. This is all well and good, so long as you design the PCB correctly.
Coupling from adjacent wires due to mutual capacitance and inductance, as well as noise in the reference ground all conspire to mangle the signal we want to pass down the wire.
As the frequencies increase, and especially if you’re dealing with sharp edges, with all that extra odd-harmonic power, things start to get bad real fast. The way we deal with this is by utilising differential-mode signalling. This is where instead of a single wire, referenced to some notion of ground, we send the signal down a pair of wires, where the voltage difference between the wires forms the signal. Any external noise that leaks into the pair, will (hopefully!) affect both wires equally, forming what we call a common-mode component. When you look at the difference, this common mode noise disappears. (Our own [Bil Herd] covered this some time ago.)
When probing a circuit, it pays to have the right kind of probe as well as an understanding of the effect the probe will have on the circuit in operation. If you have a single-ended signal and you want to view it on your scope, your choice is either a passive or active probe. Usually some kind of passive probe will be most available. These commonly come in 50 Ω and 1 MΩ versions, and you need to be careful to use the correct probe type for your application.
For probing differential signals, it is possible to use a pair of probes, one for each signal wire, and then utilise the scope’s math difference function to show the signal. This is quite often a desperate measure, and what you really want is a differential front-end in hardware. You need a differential active probe.
The circuit may be simple, but don’t underestimate how much tweaking it needs to have good performance – a little slip with the PCB layout, as the author describes, caused some annoying resonances which can be hard to track down.
The project is still under active development, with the author showing the process as the project progresses, but its looking pretty good already, if you ask us.
Sources can found on his GitHib, which uses all Open Source tools, so its pretty accessible too.
Ah, what fond memories we have of our misspent youth, walking around with a 9,000-volt electromagnetic pulse generator in our Levi’s 501s and zapping all the electronic devices nobody yet carried with them everywhere they went. Crazy days indeed.
We’re sure that’s not at all what [Rostislav Persion] had in mind when designing his portable EMP generator; given the different topologies and the careful measurement of results, we suspect his interest is strictly academic. There are three different designs presented, all centering around a battery-powered high-voltage power module, the Amazon listing of which optimistically lists as capable of a 400,000- to 700,000-volt output. Sadly, [Rostislav]’s unit was capable of a mere 9,000 volts, which luckily was enough to get some results.
Coupled to a spark gap, one of seven different coils — from one to 40 turns — and plus or minus some high-voltage capacitors in series or parallel, he tested each configuration’s ability to interfere with a simple pocket calculator. The best range for a reset and scramble of the calculator was only about 3″ (7.6 cm), although an LED hooked to a second coil could detect the EMP up to 16″ (41 cm) away. [Rostislav]’s finished EMP generators were housed in a number of different enclosures, one of which totally doesn’t resemble a pipe bomb and whose “RF Hazard” labels are sure not to arouse suspicions when brandished in public.
We suppose these experiments lay to rest the Hollywood hype about EMP generators, but then again, their range is pretty limited. You might want to rethink your bank heist plans if they center around one of these designs.
Normally, we think of lasers as pretty complex and fairly intimidating devices: big glass tubes filled with gas, carefully aligned mirrors, cooling water to keep the whole thing from melting itself, that sort of thing. Let’s not even get started on the black magic happening inside of a solid state laser. But as [Jay Bowles] shows in his latest Plasma Channel video, building a laser from scratch isn’t actually as difficult as you might think. Though it’s certainly not easy, either.
The transversely excited atmospheric (TEA) laser in question uses high voltage passed across a a pair of parallel electrodes to excite the nitrogen in the air at standard atmospheric pressure, so there’s no need for a tube and you don’t have to pull a vacuum. The setup shakes so many UV photons out of the nitrogen that it doesn’t even need any mirrors. In fact, you should be able to get almost all the parts for a TEA laser from the hardware store. For example, the hexagonal electrodes [Jay] ends up using are actually 8 mm hex keys with the ends cut off.
Hardware fault injection uses electrical manipulation of a digital circuit to intentionally introduce errors, which can be used to cause processors to behave in unpredictable ways. This unintentional behavior can be used to test for reliability, or it can be used for more nefarious purposes such as accessing code and data that was intended to be inaccessible. There are a few ways to accomplish this, and electromagnetic fault injection uses a localized electromagnetic pulse to flip bits inside a processor. The pulse induces a voltage in the processor’s circuits, causing bits to flip and often leading to unintentional behavior. The hardware to do this is very specialized, but [Pedro Javier] managed to hack a $4 electric flyswatter into an electromagnetic fault injection tool. (Page may be dead, try the Internet Archive version.)
[Pedro] accomplishes this by turning an electric flyswatter into a spark-gap triggered EMP generator. He removes the business end of the flyswatter and replaces it with a hand-wound inductor in series with a small spark gap. Pressing the power button on the modified flyswatter charges up the output capacitor until the developed voltage is enough to ionize the air in the spark gap, at which point the capacitor discharges through the inductor. The size of the spark gap determines the charge that is built up—a larger gap results in a larger charge, which produces a larger pulse, which induces a larger voltage in the chip.
Tesla Coils are a favourite here at Hackaday – just try searching through the archives, and see the number of results you get for all types of cool projects. [mircemk] adds to this list with his Extremely simple Tesla Coil with only 3 Components. But Be Warned — most Tesla coil designs can be dangerous and ought to be handled with care — and this one particularly so. It connects directly to the 220 V utility supply. If you touch any exposed, conductive part on the primary side, “Not only will it kill You, it will hurt the whole time you’re dying”. Making sure there is an ELCB in the supply line will ensure such an eventuality does not happen.
No prizes for guessing that the circuit is straight forward. It can be built with parts lying around the typical hacker den. Since the coil runs directly off 220 V, [mircemk] uses a pair of fluorescent lamp ballasts (chokes) to limit current flow. And if ballasts are hard to come by, you can use incandescent filament lamps instead. The function of the “spark gap” is done by either a modified door bell or a 220 V relay. This repeatedly charges the capacitor and connects it across the primary coil, setting up the resonant current flow between them. The rest of the parts are what you would expect to see in any Tesla coil. A high voltage rating capacitor and a few turns of heavy gauge copper wire form the primary LC oscillator tank circuit, while the secondary is about 1000 turns of thinner copper wire. Depending on the exact gauge of wires used, number of turns and the diameter of the coils, you may need to experiment with the value of the capacitor to obtain the most electrifying output.
If you have to look for one advantage of such a circuit, it’s that there is not much that can fail in terms of components, other than the doorbell / relay, making it a very robust, long lasting solution. If you’d rather build something less dangerous, do check out the huge collection of Tesla Coil projects that we have featured over the years.