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.
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.
Continue reading “Sound Isolation Box Makes Living Room Based CNC Routing Tolerable”
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.
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!]
Continue reading “What’s Inside a USB Isolator?”
[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.
[Oleg] over at Circuits@Home has made a USB isolator for his hacking needs. This isolator separates the signal, ground, and power lines of a USB host device, such as a PC, from a USB device like a USB oscilloscope or logic analyzer. This might be useful for Keyboard sniffing, ECG, EEG or diagnosing the control system on the positive ground of your autonomous Ford 8N. What other applications can you come up with for this tool?