You Can’t Make What You Can’t Measure

What’s the most-used tool on your bench? For me, it’s probably a multimeter, although that’s maybe a tie with my oscilloscope. Maybe after that, the soldering iron and wire strippers, or my favorite forceps. Calipers must rate in there somewhere too, but maybe a little further down. Still, the top place, and half of my desert-island top-10, go to measuring gear.

That’s because any debugging, investigation, or experimentation always starts with getting some visibility on the problem. And the less visible the physical quantity, the more necessary to tool. For circuits, that means figuring out where all the voltages lie, and you obviously can’t just guess there. A couple months ago, I was doing some epoxy and fiberglass work, and needed to draw a 1/2 atmosphere vacuum. That’s not the kind of quantity you can just eyeball. You need the right measurement tool.

A few weeks ago, I wrote about my disappointment in receiving a fan that wouldn’t push my coffee beans around in the homemade roaster. How could I have avoided this debacle? By figuring out the pressure differential needed and buying a fan that’s appropriately rated. But I lacked pressure and flow meters.

Now that I think about it, I could have scavenged the pressure meter from the fiberglassing rig, and given that a go, but with the cheap cost of sensors and amplifiers, I’ll probably just purpose-build something. I’m still not sure how I’ll measure the flow; maybe I’ll just cheese out and buy a cheap wind-speed meter.

When people think of tools, they mostly think of the “doers”: the wrenches and the hammers of this world. But today, let’s all raise a calibrated 350 ml glass to the “measurers”. Without you, we’d be wandering around in the dark.

The Small And Silly Synth Now Even Smaller (But Just As Silly)

What do you do when you’ve carved out a niche for yourself as a builder of small and useless synthesizers? Why, build an even smaller and less useful synthesizer, of course!

If you’ve been paying even a minimal amount of attention you’ll know right away that this comes to use from [mitxela], who while not playing with volumetric POV displays is often found building smaller and smaller synthesizers, including putting them in DIN plug shells. The current synth is based on his “Silly Synth,” which puts all the guts for the synth inside a USB connector. This time around, though, it’s USB-C, and rather than fitting everything inside the connector shell, the entire synth sits on a PCB that’s smaller than a tiny piezo speaker. The whole thing runs on a CH32V003 microcontroller, and aside from a few support components and the right-angle USB-C plug, not much else.

The PCB is what really shines in [mitxela]’s design, especially the routing. He’s got a 20-pin QFN chip on one side of the board and the USB plug right behind it on the other side to deal with, plus the big through-holes for the speaker and the physical connections on the plug. It’s quite a crowded design, but it gets the job done. What’s more, he panelized the design so that mass production is possible; the reason for this is revealed at the end of the video below.

Pretty much every time we see one of these “smallest synth” videos we’re convinced that we’re seeing the lower limit of what’s possible, but every time, [mitxela] goes ahead and proves us wrong. That’s fine, of course — we don’t mind being wrong about something like this.

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Forget The Altair! Remember The Mark-8!

Calling any one computer the first hobby computer is fraught with peril. Most people think the MITS Altair 8800, first featured in Popular Electronics back in January 1975, was the first. Some might argue that others were first, but there is no doubt that the Altair started the hobby computer revolution from a practical standpoint. However, there was another computer that almost took the crown. It, too, appeared in a magazine — Radio and Electronics. But it was in the July 1974 issue. That computer was the Mark 8, and [Artem Kalinchuk] is building a replica that you can see started in the video below. This isn’t some Arduino work-alike. He has a pile of parts and some almost authentic-looking PCBs.

The Mark 8 used the 8008, not the 8080, so it was less powerful. [Artem] has been building a replica Altair, too. Check out his YouTube channel if you are interested in those.

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Take The Minimal Pain Out Of ESP32 Programming

Perhaps without many of us realising it, our single board computers perform the task of making programming their processor or SoC a lot easier. They take care of setting the right lines or commands to put the chip in programming mode, they deal with timings, such that we simply fire our code from our dev environment without having to expend much thought. It’s not as though it’s difficult to program most microcontrollers, but there is usually a procedure to set the chip in programming mode. Tired of pressing buttons to achieve this with the ESP32, [DoganM95] took the time to create an all-in-one USB ESP32 programming board.

It’s a straightforward enough CH340C design that also has a USBC-PD chip on-board allowing powering of an attached ESP32 from PD sources. It’s all the stuff you’d find incorporated on a little dev board, without the ESP32, so while it’s nothing earth-shattering it’s also a neat and useful little addition to your arsenal. Unsurprisingly it’s not the first time someone’s created a similar board for a commercially available ESP32 module.

Inside Electronic Gain Control

Normally, if you want to control the gain of an amplifier, you’ll use a variable resistor. You know, like a volume control. But what if you want to control the amplifier’s gain with a voltage? [Engineering Prof] explains a circuit that can do this using a pair of op amps and a pair of matched JFETs.

The analysis is simple because you assume the op amps are not in saturation, so you can assume that the op amp will do what it needs to do to make the input terminals equal. The left-hand op amp has one input grounded, so the output will drive the first FET  to ensure the negative terminal is also 0V. It is easy to see that the current through R1 must then be the current through the FET, which is going to be the control voltage (which is negative) divided by R1.

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1D LED PONG, Arduino-Style

Maybe it’s just us, but isn’t it kind of amazing that in a world of pretty darn realistic games, PONG is still thrilling to play? This 1D implementation by [newsonator] is about as exciting as it gets.

It works like you’d probably expect — the light moves back and forth between the two players. Keep it in the green and you have a nice, gentle volley going. Let it hit your red LED and you’ve lost a point. But if you can push your button while your yellow LED is lit, the light speeds up tremendously until the next button press in the green.

Our only wish is that subsequent yellow-light button presses would make it speed up even more. But there are really just the two speeds with the current programming.

Inside the cool laser-cut box is an Arduino Uno and a 9V battery, plus a current-limiting resistor and the all-important buzzer. We like how [newsonator] wired up the LEDs to the Arduino by soldering them to a row of header pins and sticking that into the Arduino so it can be used in other projects down the line. We also like how [newsonator] shoved a couple of dowels through the box to ultimately support the two buttons.

Check out the intro video after the break for the overall details. The build is done over a few different short videos which follow.

Although this is pretty small, it isn’t quite the minimum viable.

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Repairing An HP Power Supply

One of the interesting things about living in modern times is that a confluence of the Internet and rapid changes in the electronics industry means that test gear that used to be astronomically priced is now super affordable. Especially if, like [Frankie Mashockie], you can do a little repair work. He picked up an HP6038A power supply for $50. We couldn’t find the original list price, but even refurbs from “professional” sources go for around $800. However, the $50 price came with a “for parts” disclaimer.

The power supply is autoranging. You usually think of that as a feature of meters. In a power supply, autoranging means the device can adjust the voltage based on load as you can see explained in the video below.

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