Multiply Your Multimeter With Relays And USB

April 2, 2024 by Dan Maloney 10 Comments

Multimeters are a bit like potato chips: you can’t have just one. But they’re a lot more expensive than potato chips, especially the good ones, and while it’s tempting to just go get another one when you need to make multiple measurements, sometimes it’s not practical. That’s why something like this 2×4 relay-based multiplexer might be a handy addition to your bench

In this age of electronics plenty, you’d think that a simple USB relay board would be easy enough to lay hands on. But [Petteri Aimonen] had enough trouble finding a decent one that it became easier to just roll one up from scratch. His goal was to switch both the positive and negative test leads from up to four instruments to a common set of outputs, and to have two independent switching banks, for those times when four-lead measurements are needed. The choice of relay was important; [Petteri] settled on a Panasonic DPDT signal relay with low wetting current contacts and a low-current coil. The coils are driven by a TBD62783A 8-channel driver chip, while an STM32 takes care of USB duties.

The mechanical design of this multiplexer is just as slick as the electrical. [Petteri] designed the PCB to act as the cover for a standard Hammond project box, so all the traces and SMD components are mounted on the back. That just leaves the forest of banana-plug binding posts on the front, along with a couple of pushbuttons for manual input switching and nicely silkscreened labels. The multiplexer is controlled over USB using the SCPI protocol, which happily includes an instrument class for signal switchers.

We think the fit and finish on this one is fantastic, as is usual with one of [Petteri]’s builds. You’ll probably recall his calibrated current reference or his snazzy differential probe.

Modular Vacuum Table Custom-Fits The Parts

March 31, 2024 by Donald Papp 3 Comments

[enhydra] needed to modify a bunch of side inserts from some cheap ABS enclosures, and to save time and effort, he created a simple vacuum table with swappable inserts to precisely fit the parts. Suction is provided by a shop vacuum (plugged in near the bottom in the photo above) and it worked very well! Sealing and gaskets weren’t even required.

A vacuum table provides a way to hold workpieces flat and secure while a CNC machine does its thing, and because no clamps are involved, it can really speed up repetitive work. [enhydra]’s solution combines a vacuum table with a jig that ensures every rectangular piece is held exactly where the machine expects it to be, making the whole process of modifying multiple units significantly more efficient.

The whole thing — vacuum table and modular top — was straightforward to CNC cut out of what looks like particle board and worked as-is, no added gaskets or seals required, making this a very economical solution.

Vacuum tables can be pretty versatile and applied in more than one way, so keep that in mind the next time you’re wondering how best to approach a workshop problem. We’ve seen a well-engineered table used to speed up PCB milling, and we’ve also seen a DIY vacuum table combined with a heat gun and plastic plates from the dollar store make a bare-bones thermoforming rig.

SMD Soldering, Without The Blobs

March 30, 2024 by Jenny List 23 Comments

Hand soldering of surface mount components is a bread-and-butter task for anyone working with electronics in 2024. So many devices are simply no longer available in the older through-hole formats, and it’s now normal for even the most homebrew of circuits to use a PCB. But how do you solder your parts? If like us you put a blob of solder on a pad and drop the part into it, then [Mr. SolderFix] has some advice on a way to up your game.

The blob of solder method leaves a little more solder on the part than is optimal, sometimes a bulbous lump of the stuff. Instead, he puts a bit of flux on the pad and then applies a much smaller quantity of solder on the tip of his iron, resulting in a far better joint. As you can see in the video below, the difference is significant. He starts with passives, but then shows us the technique on a crystal, noting that it’s possible to get the solder on the top of these parts if too much is used. Yes, we’ve been there. Watch the whole video, and improve your surface mount soldering technique!

He’s someone we’ve featured before here at Hackaday, most recently in lifting surface mount IC pins.

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Night Vision The Old Way

March 26, 2024 by Al Williams 7 Comments

Solid state electronics have provided lighter weight night vision units that work better than the old-fashioned gear that used photomultiplier tubes, but there was an even older technology as [Our Own Devices] shows us in a recent video. The Metascope Type B was a first-generation passive night vision viewer that relied on moonlight.

The video shows a 1946 technical paper from the Office of Scientific Research and Development with [Vannevar Bush] credited as the institute’s director. If that name sounds familiar, you may remember that he foresaw hypertext (inspiring both [Doug Englebart] and the creation of the Web).

The Type B was an improvement over the older Type A, which had been tested during the invasion of North Africa in 1942. The type A weighed less than two pounds and was much smaller than the type B. However, it didn’t work very well, so they stopped making them and did a redesign, which is what you see in the video. The type B weighed almost 5 pounds.

To use the metascope, you had to “charge” it with light and then wait. Eventually, you’d need to charge it again. The type B allowed you to charge one phosphor plate while using another one. When that plate became weak, you could swap the plates to continue using the device.

If you aren’t keen on the history, you can skip to just before the 15-minute mark of the video for the hardware examination. He doesn’t open the device, but that’s probably wise, given the nature, age, and rarity of the metascope.

Modern image sensors are very sensitive to infrared, and normal cameras usually have filters to keep them out. Not that you can’t remove it, of course. If you want to see something more modern, [Nick] built his own AN/PVS-14 night vision scope and you can too.

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Are Minimills Worth It?

March 25, 2024 by Al Williams 64 Comments

These days, the bar for home-built projects is high. With 3D printers, CNC, and cheap service providers, you can’t get away with building circuits in a shoe box or an old Tupperware container. While most people now have access to additive manufacturing gear, traditional subtractive equipment is still a bit less common. [Someone Should Make That] had thought about buying a “minimill” but he had read that they were not worth it. Like a lot of us, he decided to do it anyway. The pros and cons are in the video you can watch below.

During setup, he covered a few rumors he’d heard about these type of mills, including they are noisy, have poor tolerances, and can’t work steel. Some of these turned out to be true, and some were not.

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AxxSolder 3.0 Now Takes USB Power Delivery

March 25, 2024 by Lewin Day 12 Comments

If you’re big into the soldering iron scene, you’ve probably heard of the AxxSolder project. Now, it’s been updated with a whole host of nifty new features. It’s AxxSolder 3.0!

If you’re not intimately familiar with AxxSolder, it’s an open-source iron design based around the popular JBC soldering iron tips. Relying on the STM32G431CBT6 to run the show, it comes in two versions—a lightweight portable design, and a desktop version based around the JBC ADS soldering iron stand. So far, so familiar.

The new 3.0 version adds new functionality, however. Where the previous model ran off any old DC power source from 9 to 26 volts, the new version can run off a USB Power Delivery supply. Thus, you can grab any old USB-PD device, like a laptop charger, and run your iron off that.

The new version also uses a larger color TFT screen with some buttons added on as an improved user interface. Thermal performance is improved, and it’s additionally capable of measuring the current draw by the tip, so you can monitor the performance of the iron in great detail.

We’ve featured the AxxSolder project previously, too, along with some other great soldering iron projects. If you reckon you’ve just designed the hottest new soldering tool yourself, let us know about it!

A raspberry pi-based digital readout above an old lathe

Roll Your Own DRO With An Added Twist

March 22, 2024 by Dave Rowntree 3 Comments

When using a manual machine tool such as a lathe or milling machine, there can be a lot of pressure to read the position and feed the axes at the correct rate. That’s why modern machines typically have some form of digital read-out (DRO). [Stefano Bertelli] has created a simple Raspberry Pi based DRO with an additional twist, that of a linked motor drive output.

A view of the custom RS485 interfaced DRO readout and motor controller — Realtime encoder position reading and motor control are best done with a dedicated microcontroller, ideally with a proper RTOS.

The axes that need to be monitored should be mechanically attached to a position sensor like a linear encoder or a rotary type. Using a linear sensor with a linear axis instead of a rotary encoder on the downstream dial is better. For the readout unit, [Stefano] used a WaveShare 7-inch touchscreen module with a Raspberry Pi 3 for the UI of the readout unit. The Pi has a custom-designed HAT, that performs power conditioning and provides a robust RS485 interface. Connected via that RS485 link is another custom PCB based on an STM32F411 with a few supporting power supplies and interfacing components. The job of this board is to interface to the position encoders, reading positioning pulses using interrupts. There is an additional stepper motor drive courtesy of a ULN2003 Darlington driver to allow the control of a single motorised axis. An additional motor driver module is required, which should be no surprise since driving a milling machine axis will require a fairly beefy motor. This GitHub repo contains the FreeRTOS-based firmware for this board. This motor drive has the ability to be connected to a measuring axis in a programmable way, enabling one axis to be adjusted to follow or jump in controlled steps with another. This feature can significantly simplify certain types of machining operations, as [Stefano] elaborates in the video.

Lastly, the Raspberry Pi runs a simple Python application with Kivy for the GUI. As [Stefano] explains in the video below, this makes debugging and modification quite simple.

Adding DROs to an older machine is an obvious but valuable hack. Here’s another way to do it. If that’s too much work, then you could just hack a digital readout calliper in there.

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