[Ben Krasnow] Makes A DSKY

May 19, 2019 by Dan Maloney 6 Comments

There are hundreds if not thousands of artifacts from the Apollo program scattered around the globe, some twisted wrecks at the bottom of the ocean, others lovingly preserved and sitting in museums or in the hands of private collectors. All of what’s left is pretty much pure unobtainium, so if you want something Apollo-like, you’re probably going to have to make it yourself.

[Ben Krasnow] took up the challenge to make an electroluminescent Apollo-era DSKY display from scratch, with outstanding results. The DSKY, or “display and keyboard”, was the user interface for the Apollo Guidance Computer, the purpose-built digital navigation system that got a total of 24 men there and back again. [Ben] says it took a long time to recreate the display, and we can see why. He needed to master quite a few skills, including screen printing to get the glass-panel display working. The panel is a sandwich of phosphorescent paint, a dielectric, and conductive ink. The ink is silkscreened on the back to form the characters, all applied to indium tin oxide (ITO) conductive glass. A PCB with the same pattern of character segments lays behind that, driving each segment with 300 volts or so through a trio of HV507 high-voltage shift registers. It’s an impressive bit of engineering and gives off a decidedly not-homebrew vibe.

In the video below, [Ben] goes into detail about the trials he experienced on the way to this amazing endpoint, not least of which was frying chip after chip due to ineffective protection diodes in the shift registers. That’s an epic debugging story that’s worth the price of admission all by itself. It’s not the only DSKY in town, of course – [Fran Blanche] has been working on one for a while too – but there’s just something about that blue glow that we really like.

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The $50 Ham: Dummy Loads, Part 2

May 17, 2019 by Dan Maloney 21 Comments

In the last installment of “The $50 Ham” I built a common tool used by amateur radio operators who are doing any kind of tuning or testing of transmitters: a dummy load. That build resulted in “L’il Dummy”, a small dummy load intended for testing typical VHF-UHF handy talkie (HT) transceivers, screwing directly into the antenna jack on the radio.

As mentioned in the comments by some readers, L’il Dummy has little real utility. There’s actually not much call for a dummy load that screws right into an HT, and it was pointed out that a proper dummy load is commercially available on the cheap. I think the latter observation is missing the point of homebrewing specifically and the Hackaday ethos in general, but I will concede the former point. That’s why at the same time I was building L’il Dummy, I was building the bigger, somewhat more capable version described here: Big Dummy.

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Video: Putting High Speed PCB Design To The Test

January 24, 2019 by Bil Herd 48 Comments

Designing circuit boards for high speed applications requires special considerations. This you already know, but what exactly do you need to do differently from common board layout? Building on where I left off discussing impedance in 2 layer Printed Circuit Board (PCB) designs, I wanted to start talking about high speed design techniques as they relate to PCBs. This is the world of multi-layer PCBs and where the impedance of both the Power Delivery Network (PDN) and the integrity of the signals themselves (Signal Integrity or SI) become very important factors.

I put together a few board designs to test out different situations that affect high speed signals. You’ve likely heard of vias and traces laid out at right angles having an impact. But have you considered how the glass fabric weave in the board itself impacts a design? In this video I grabbed some of my fanciest test equipment and put these design assumptions to the test. Have a look and then join me after the break for more details on what went into this!

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A Look At Liquid Dielectrics

September 18, 2018 by Dan Maloney 34 Comments

One evening quite a few years ago, as I was driving through my hometown I saw the telltale flashing lights of the local volunteer fire department ahead. I passed by a side road where all the activity was: a utility pole on fire. I could see smoke and flames shooting from the transformer and I could hear the loud, angry 60 Hz buzzing that sounded like a million hornet nests. As I passed, the transformer exploded and released a cloud of flaming liquid that rained down on the road and lawns underneath. It seemed like a good time to quit rubbernecking and beat it as fast as I could.

I knew at the time that the flaming liquid was transformer oil, but I never really knew what it was for or why it was in there. Oil is just one of many liquid dielectrics that are found in a lot of power distribution equipment, from those transformers on the pole to the big capacitors and switchgear in the local substation. Liquid dielectrics are interesting materials that are worth taking a look at.

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Low-Quality Capacitors Turned Into High-Quality Temperature Sensors

August 23, 2018 by Dan Maloney 19 Comments

When life hands you a bunch of crummy capacitors, what do you do? Make a whole bunch of temperature sensors, apparently.

The less-than-stellar caps in question came to [pyromaniac303] by way of one of those all-in-one assortment kits we so love to buy. Stocked with capacitors of many values, kits like these are great to have around, especially when they’ve got high-quality components in them. But not all ceramic caps are created equal, and [pyromaniac303] was determined not to let the lesser-quality units go to waste. A quick look at the data sheets revealed that the caps with the Y5V dielectric had a suitably egregious temperature coefficient to serve as a useful sensor. A fleck of perf-board holds a cap and a series resistor; the capacitor is charged by an Arduino output pin through the resistor, and the time it takes for the input pin connected to the other side of the cap to go high is measured. Charge time is proportional to temperature, and a few calibration runs showed that the response is pretty linear. Unfortunately the temperature coefficient peaks at 10°C and drops sharply below that point, making the sensor useful only on one side of the peak. Still, it’s an interesting way to put otherwise unloved parts to use, and a handy tip to keep in mind.

Temperature sensing isn’t the only trick capacitors can do. We’ve seen them turned into touch sensors before, and used to turn a 3D-printer into a 3D-scanner.

Oil-Immersed Raspberry Pi Keeps Its Cool Under Heavy Loads

August 13, 2018 by Dan Maloney 58 Comments

As a general rule, liquids and electronics don’t mix. One liquid bucks that trend, though, and can contribute greatly to the longevity of certain circuits: oil. Dielectric oil cools and insulates everything from the big mains transformers on the pole to switchgear in the substation. But what about oil for smaller circuits?

[Lord_of_Bone] was curious to see if an oil-cooled Raspberry Pi is possible, and the short answer is: for the most part, yes. The experimental setup seen in the video below is somewhat crude — just a Pi running Quake 3 for an hour to really run up the CPU temperature, which is monitored remotely. With or without heatsinks mounted, in free air the Pi ranges from about 50°C at idle to almost 70°C under load, which is pretty darn hot. Dunking the Pi in a bath of plain vegetable oil, which he admits was a poor choice, changes those numbers dramatically: 37°C at idle and an only warmish 48°C after an hour of gaming. He also tested the Pi post-cleaning, which is where he hit a minor hiccup. The clean machine started fine but suffered from a series of reboots shortly thereafter. Twelve hours later the Pi was fine, though, so he figures a few stray drops of water that hadn’t yet evaporated were to blame.

Is oil immersion a practical way to cool a Pi? Probably not. It doesn’t mean people haven’t tried it before, of course, but we applaud the effort and the careful experimentation.

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DIY Capacitive Rotational Encoder On The Cheap With FR4

November 17, 2017 by Donald Papp 15 Comments

Rotary encoders are critical to many applications, even at the hobbyist level. While considering his own rotary encoding needs for upcoming projects, it occurred to [Jan Mrázek] to try making his own DIY capacitive rotary encoder. If successful, such an encoder could be cheap and very fast; it could also in part be made directly on a PCB.

First prototype, two etched plates with transparent tape as dielectric material. Disc is 15 mm in diameter.

The encoder design [Jan] settled on was to make a simple adjustable plate capacitor using PCB elements with transparent tape as the dielectric material. This was used as the timing element for a 555 timer in astable mode. A 555 in this configuration therefore generates a square wave that changes in proportion to how much the plates in the simple capacitor overlap. Turn the plate, and the square wave’s period changes in response. Response time would be fast, and a 555 and some PCB space is certainly cheap materials-wise.

The first prototype gave positive results but had a lot of problems, including noise and possibly a sensitivity to temperature and humidity. The second attempt refined the design and had much better results, with an ESP32 reliably reading 140 discrete positions at a rate of 100 kHz. It seems that there is a tradeoff between resolution and speed; lowering the rate allows more positions to be reliably detected. There are still issues, but ultimately [Jan] feels that high-speed capacitive encoders requiring little more than some PCB real estate and some 555s are probably feasible.

This project is a reminder that FR4 (whether copper-clad, etched, or blank) shows up in clever applications: copper tape and blank FR4 can be used to quickly prototype RF filters, PocketNC built an entire small CNC tool around FR4, and our own [Voja] wrote a full guide on making beautiful enclosures from FR4.