High Current Measurement Probe For Oscilloscopes

April 11, 2021 by Anool Mahidharia 22 Comments

A decent current measurement sensor ought to be an essential part of every hacker’s workbench. One that is capable of measuring DC, as well as low and high frequencies with reasonable accuracy. And bonus credits if it can also withstand high bus voltages – such as those found in mains utility or electric vehicle work. [Undersilicon] couldn’t find one that ticked all the boxes, so he built an ACS730 based AC/DC current probe capable of measuring up to 25 A at frequencies up to 1 MHz.

Allegro Microsystems has a wide offering of current sensor IC’s. The ACS730 features a -3 dB bandwidth of 1 MHz, and -1 dB bandwidth of 500 kHz. Since it is galvanically isolated, it can be used in AC mains applications up to 297 Vrms and for DC up to 420 V. And as he intended to use it as an oscilloscope accessory, the analog output suited the application nicely. A pair of precision op-amps provide the voltage output scaled to 100 mV/A. The board is powered off a 1000 mAh LiPo battery that can run the sensor for about 15 ~ 20 hours. The power supply section consists of a charge circuit for the LiPo, and a split rail dual output power supply converter for the op-amps.

The ACS730 has a 2.5 V output when measured current is zero, and is scaled for 40 mV/A. This gives an output voltage swing from -0.5 V for -50 A to +4.5 V for +50 A. This is where the AD823ARZ dual 16 MHz, Rail-to-Rail FET Input Amplifiers step in. One pair is used to obtain a 2.5 V reference from the 5 V supply, and also to buffer the analog output from the ACS730. The second pair subtracts the 2.5 V offset, and applies a gain of 2.5 to get the 100 mV/A output. Dual power supply for the op-amps comes from a TPS65133 Split-Rail Converter, ±5V, 250mA Dual Output Power Supply. Lastly, LiPo charging is handled by the MCP73831 Single Cell, Li-Ion/Li-Polymer Charge Management Controller.

Initial testing of direct currents has shown fairly accurate performance. But he’s observed some noise when measuring currents below 1 A which requires some debugging to figure out the source. [Undersilicon] has provided the CAD files for both the PCB and 3D printed enclosure, giving you access to everything you need to build one yourself. If you’re looking for something a bit more heavy duty, you might be interested in this +/-50 A, 1.5 MHz sensor encased in concrete.

Engineering The Less Boring Way

April 9, 2021 by Al Williams 6 Comments

We have to admire a YouTube channel with the name [Less Boring Lectures]. After all, he isn’t promising they won’t be boring, just less boring. Actually though, we found quite a few of the videos pretty interesting and not boring at all. The channel features videos about mechanical engineering and related subjects like statics and math. While your typical electronics project doesn’t always need that kind of knowledge, some of them do and the mental exercise is good for you regardless. A case in point: spend seven minutes and learn about 2D and 3D vectors in two short videos (see below). Or spend 11 minutes and do the whole vector video in one gulp.

These reminded us of Kahn Academy videos, although the topics are pretty hardcore. For example, if you want to know about axial loading, shear strain, or free body diagrams, this is a good place to look.

Continue reading “Engineering The Less Boring Way” →

Review: What On Earth Is An Electromagnetic Radiation Tester And Why Would I Need One?

April 7, 2021 by Jenny List 75 Comments

One of the joys of an itinerant existence comes in periodically being reunited with the fruits of various orders that were sent to hackerspaces or friends somewhere along the way. These anonymous parcels from afar hold an assortment of wonders, with the added element of anticipation that comes from forgetting exactly what had been ordered.

So it is with today’s subject, a Mustool MT525 electromagnetic radiation tester. At a cost not far above £10 ($13.70), this was an impulse purchase driven by curiosity; these devices claim to measure both magnetic and electric fields, but what do they really measure? My interest in these matters lies in the direction of radio, but I have never examined such an instrument. Time to subject it to the Hackaday treatment.

Continue reading “Review: What On Earth Is An Electromagnetic Radiation Tester And Why Would I Need One?” →

Electric Window Motor Becomes Mini Chainsaw

April 2, 2021 by Donald Papp 13 Comments

This mini handheld chainsaw by [Make it Extreme] is based around an electric motor from a car door, the same ones used to raise and lower car windows. They are common salvage parts, and with the right modifications and a few spare chainsaw bits attached, it turns out that the motor is more than capable of enough zip to cut through a variety of wood. Add a cordless tool battery pack, and the portable mini handheld chainsaw is born.

What’s really remarkable about the build video (embedded below, after the break) is not simply that it shows the build process and somehow manages to make it all look easy. No, what’s truly remarkable is that in the video it is always clear what is happening, and all without a single word being spoken. There’s no narration, no watching someone talk, just a solid build and demonstration. The principle of “show, don’t tell” is definitely taken to heart, here.

So, how well does it work as a chainsaw? It seems to work quite well! [Make it Extreme] does feel that a chain with smaller teeth and a higher motor speed would probably be an improvement, but the unit as built certainly can cut. You can judge for yourself by watching the build video, embedded below.

Continue reading “Electric Window Motor Becomes Mini Chainsaw” →

Extinguish Squeaks 24/7 With Refillable WD-40

April 1, 2021 by Kristina Panos 43 Comments

It’s 10:34PM and you’ve just run out of water displacement formula #40. You could wait until tomorrow to get a new can, or you could spend the rest of the night turning an old, empty fire extinguisher into a refillable and re-pressurizable WD-40 dispenser like [liquidhandwash] did. The part count is pretty low, but it’s awfully specific.

And the emphasis is on empty extinguisher. Part of the deal involves twisting the gauge off, and we wouldn’t want you to get blasted in the face with any last gasps of high-powered firefighting foam. In order to make the thing re-pressurizable, [liquidhandwash] stripped all the rubber from a tire valve and removed the core temporarily so it could be soldered into the fitting where the gauge was. The handy hose is from a large can of WD-40, which is also where the label came from — since it’s no longer a fire extinguisher, it needs to stop bearing resemblance to one, so [liquidhandwash] removed the sticker, painted it blue, and glued the cut-open can to the outside.

To use it, [liquidhandwash] fills it up about halfway and then pressurizes it through the tire valve with a bike pump or compressor. (We think we’d go with bike pump.) Since [liquidhandwash] goes through so much lubricant, now, they can just buy it by the gallon and keep refilling the extinguisher.

Is WD-40 your everything hammer? Variety is the spice of shop life.

Wires Vs Words — PCB Routing In Python

March 30, 2021 by Chris Lott 30 Comments

Preferring to spend hours typing code instead of graphically pushing traces around in a PCB layout tool, [James Bowman] over at ExCamera Labs has developed CuFlow, a method for routing PCBs in Python. Whether or not you’re on-board with the concept, you have to admit the results look pretty good.

Key to this project is a concept [James] calls rivers — the Dazzler board shown above contains only eight of them. Connections get to their destination by taking one or more of these rivers which can be split, joined, and merged along the way as needed in a very Pythonic manner. River navigation is performed using Turtle graphics-like commands such as left(90) and the appropriately named shimmy(d)that aligns two displaced rivers. He also makes extensive use of pin / gate swapping to make the routing smoother, and there’s a nifty shuffler feature which arbitrarily reorders signals in a crossbar manner. Routing to complex packages, like the BGA shown, is made easier by embedding signal escapes for each part’s library definition.

We completely agree with [James]’s frustration with so many schematics these days being nothing more than a visual net lists, not representing the logical flow and function of the design at all. However, CuFlow further obfuscates the interconnections by burying them deep inside the wire connection details. Perhaps, if CuFlow were melded with something like the SKiDL Python schematic description language, the concept would gain more traction?

That said, we like the concept and routing methodologies he has implemented in CuFlow. Check it out yourself by visiting the GitHub repository, where he writes in more detail about his motivation and various techniques. You may remember [James] two of his embedded systems development tools that we covered back in 2018 — the SPI Driver and the I2C driver.

Put The Perfect Point On Your Tungstens With This Die Grinder Attachment

March 29, 2021 by Dan Maloney 14 Comments

Aspiring TIG welders very quickly learn the importance of good tungsten electrode grinding skills. All it takes is a moment’s distraction or a tiny tremor in the torch hand to plunge the electrode into the weld pool, causing it to ball up and stop performing its vital function. Add to that the fussy nature of the job — tungstens must only be ground parallel to the long axis, never perpendicular, and at a consistent angle — and electrode maintenance can become a significant barrier to the TIG beginner.

A custom tungsten grinder like this one might be just the thing to flatten that learning curve. It comes to us by way of [The Metalist], who turned an electric die grinder into a pencil sharpener for tungsten electrodes. What we find fascinating about this build is the fabrication methods used, as well as the simplicity of the toolkit needed to accomplish it. The housing of the attachment is built up from scraps of aluminum tubing and sheet stock, welded together and then shaped into a smooth, unibody form that almost looks like a casting. Highlights include the mechanism for adjusting the angle of the grind as well as the clever way to slit the body of the attachment so it can be clamped to the nosepiece of the die grinder. We also thought the inclusion of a filter to capture tungsten dust was a nice touch; most TIG electrodes contain a small amount of lanthanum or thorium, so their slight radioactivity is probably best not inhaled.

We love builds like this that make a tedious but necessary job a little quicker and easier to bear, and anything that stands to make us a better welder — from simple purpose-built fixtures to large-scale rotary tables — is OK in our book.

Continue reading “Put The Perfect Point On Your Tungstens With This Die Grinder Attachment” →