High Voltage Measurement is Shockingly Safe

With the right equipment and training, it’s possible to safely work on energized power lines in the 500 kV range with bare hands. Most of us, though, don’t have the right equipment or training, and should take great care when working with any appreciable amount of voltage. If you want to safely measure even the voltages of the wiring in your house there’s still substantial danger, and you’ll want to take some precautions like using isolated amplifiers.

While there are other safe methods for measuring line voltage or protecting your oscilloscope, [Jason]’s isolated amplifier method uses high voltage capacitors to achieve isolation. The input is then digitized, sent across the capacitors, and then converted back to an analog signal on the other side. This project makes use of a chip from TI to provide the isolation, and [Jason] was able to build it on a perfboard while making many design considerations to ensure it’s as safe as possible, like encasing high voltage sections in epoxy and properly fusing the circuit.

[Jason] also discusses the limitations of this method of isolation on his site, and goes into a lot of technical details about the circuit as well. It probably wouldn’t get a UL certification, but the circuit performs well and even caught a local voltage sag while he was measuring the local power grid. If this method doesn’t meet all of your isolation needs, though, there are a lot of other ways to go about solving the problem.

A Sneak Peek at Anechoic Chamber Testing

[Mathieu Stephan] has something new in the works, and while he isn’t ready to take the wraps off of it yet, he was kind enough to document his experience putting the mysterious new gadget through its paces inside an anechoic chamber. Considering the majority of us will never get inside of one of these rooms, much less have the opportunity to test our own hardware in one, he figured it was the least he could do.

If you’re not familiar with an anechoic chamber, don’t feel bad. It’s not exactly the sort of thing you’ll have at the local makerspace. Put simply it’s a room designed to not only to remove echos on the inside, but also be completely isolated from the outside. But we aren’t just talking about sound deadening, the principle can also be adapted to work for electromagnetic waves. So not only is in the inside of the anechoic chamber audibly silent, it can also be radio silent.

This is important if you want to test the performance of things like antennas, as it allows you to remove outside interference. As [Mathieu] explains, both the receiver and transmitter can be placed in the chamber and connected to a vector network analyzer (VNA). The device is able to quantify how much energy is being transferred between the two devices, but the results will only be accurate if that’s the only thing the VNA sees on its input port.

[Mathieu] can’t reveal images of the hardware or the results of the analysis because that would give too much away at this point, but he does provide the cleverly edited video after the break as well as some generic information on antenna analysis and the type of results one receives from this sort of testing. Our very own [Jenny List] has a bit more information on the subject if you’d like to continue to live vicariously through the accounts of others. For the rest of us, we’ll just have to settle for some chicken wire and a wooden crate.

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Isolated Voltage Measurements Through Frequency

This one’s not a flashy hack, it’s a great piece of work and a good trick to have up your sleeve. Sometimes you’ve got a voltage difference that you’d like to measure, but either the ground potential is at a different level, or the voltages are too high for your lowly microcontroller.

There are tons of tricks with resistive voltage dividers that you can play. But if you want serious electrical isolation from the target, there’s only one way to go — an optocoupler. But optocouplers only really transmit digital signals, and [Giovanni Carrera] needed to measure an analog voltage.


Enter the voltage-to-frequency IC that does just what it says: produces a square wave with a frequency that’s proportional to the voltage applied. Pass this square wave through an optocoupler, and you can hit one side with voltages approaching lightning strikes without damaging the microcontroller on the other side. And you’re still able to measure the voltage accurately by measuring the frequency on the digital I/O pins of the microcontroller.

[Giovanni] built up and documented a nice circuit. He even tested it for linearity. If you’re ever in the position of needing to measure a voltage in a non-traditional way, you’ll thank him later.

Sound Isolation Box Makes Living Room Based CNC Routing Tolerable

CNC Machines can be loud, especially if they are equipped with a high-speed router spindle. Unfortunately, such a loud racket could be a problem for the apartment dwellers out there. Fear Not! [Petteri] has come up with a solution. It’s a sound isolation enclosure for his mini CNC Router that doubles as furniture. It keeps the sound and dust in while pumping out some cool parts….. in his living room.

What may just look like a box with an upholstered top actually had a lot of thought put into the design. The front MDF panel folds down to lay flat on the floor so that the user can kneel on it to access the machine without putting unnecessary stress on the door hinges. The top also is hinged to allow some top-down access or permit a quick peek on the status of a job. All of the internal corners of the box were caulked to be air tight, even a little air passageway would allow sound and dust to escape. Two-centimeter thick sound insulation lines the entire interior of the box and the two access lids have rubber sealing strips to ensure an air tight seal when closed.

With stepper motors, the spindle motor and control electronics all running inside an enclosed box, there is some concern over heat build up. [Petteri] hasn’t had any problems with that so far but he still installed an over-temp power cutoff made from a GFCI outlet and a thermostat temperature switch. This unit will cut the mains power if the temperature gets over 50º C by intentionally tripping the GFCI outlet. None of the internal parts will ignite under 300º C, so there is quite a safety buffer.

Although the isolation box came out pretty good, [Petteri] admits there is room for improvement; when cutting wood or aluminum, the noise level is kind of annoying. If he had to do it again, he would use thicker MDF, 20mm instead of 5mm. However, during general use while cutting plastic, the router is still quieter than his dishwasher.

Video below.

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Galvanic Isolated FTDI Board Saves Your USB Ports

Isolated FTDI circuitg

We work with some dangerous circuits in the pursuit of cool hacks. High voltage, high current, all demand some respect. We can protect our bodies easily enough, but what about that fancy new laptop or Macbook? [David] is here to help with his isolated versatile FTDI circuit.

Our computers are often wired directly into the circuits we’re hacking on. In days past that might have been a parallel or serial port. Today it’s almost always USB, specifically serial over USB. USB has some safety features built-in, such as current limiting. However, it isn’t too hard to blow up a USB port, or even a motherboard with high voltage. Galvanic isolation is a method of removing any electrical connection between two circuits. Connections can still be made through optical, magnetic, or capacitive methods, just to name a few. One of the simplest methods of galvanic isolation is the humble optocoupler.

Isolating a high-speed USB connection can get somewhat complex. [David] wisely chose to isolate things on the serial side of the FTDI USB to serial converter. He started with SparkFun’s open source FTDI Basic Breakout. Galvanic isolation is through either an Analog Devices ADuM 1402 or ADuM 5402. The 1402 needs a bit of power on the isolated side, while the 5402 includes an isolated DC/DC converter to provide up to 60mA.

[David] didn’t just stop at galvanic isolation. He also added ESD protection, over current protection, and multiple options which can be selected when the board is built. Nice work [David]! Now we don’t have to worry about our laptop frying when we’re blowing up wires.

What’s Inside a USB Isolator?

Coil Die


In this acid powered teardown, [Lindsay] decapped a USB isolator to take a look at how the isolation worked. The decapped part is an Analog Devices ADUM4160. Analog Devices explains that the device uses their iCoupler technology, which consists of on chip transformers.

[Lindsay] followed [Ben Krasnow]’s video tutorial on how to decap chips, but replaced the nitric acid with concentrated sulphuric acid, which is a bit easier to obtain. The process involves heating the chip while applying an acid. Over time, the packaging material is dissolved leaving just the silicon. Sure enough, one of the three dies consisted of five coils that make up the isolation transformers. Each transformer has 15 windings, and the traces are only 4μm thick.

After the break, you can watch a time lapse video of the chip being eaten by hot acid. For further reading, Analog Devices has a paper on how iCoupler works [PDF warning].

[Thanks to Chris for the tip!]

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Building an isolation booth for your home recording studio

[Brattonwvu] wanted to lay down some tracks with as high an audio quality as possible. To help get rid of the noise pollution of the everyday world he built this isolation booth in his attic.

The project started off with a trip to the home store for some 2×4 stock and OSB to use as sheathing. The framing is as you would expect, but to help deaden the sound he went with a surprising material. He’s filled the cavities between each 2×4 with stuffed animals and old clothes. The same is done in the walls and the inside surfaces are all covered in fabric to prevent echoing. The door has a lip and we can just make out what looks like weather stripping to provide a seal. There is just one opening in the box, where a PVC pipe allows electrical and microphone cables to pass through. [Brattonwvu] reports that you can hear your heartbeat in your ears when standing inside the sealed booth.