Darth Vader, In A Nixie Tube

This may be a controversial statement, but Nixie tubes have become a little passé in our community. Along comes another clock project, and oh look! It’s got Nixie tubes instead of 7-segment displays or an LCD. There was a time when this rediscovered archaic component was cool, but face it folks, it’s been done to death. Or has it?

vadar-nixie-tube-unlitSo given a disaffection with the ubiquity of Nixies you might think that no Nixie project could rekindle that excitement. That might have been true, until the videos below the break came our way. [Tobias Bartusch] has made his own Nixie tube, and instead of numerals it contains a 3D model of [Darth Vader], complete with moving light saber. Suddenly the world of Nixies is interesting again.

The first video below the break shows us the tube in action. We see [Vader] from all angles, and his light saber. Below that is the second video which is a detailed story of the build. Be warned though, this is one that’s rather long.

The model is made by carefully shaping and spot welding Kanthal wire into the sculpture, a process during which (as [Tobias] says) you need to think like neon plasma. It is then encased in a cage-like structure which forms its other electrode. He takes us through the process of creating the glass envelope, in which the wire assembly is placed. The result is a slightly wireframe but very recognisable [Vader], and a unique tube.

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Get to Know 3½ Digit ADCs with the ICL71xx

Riffling through my box of old projects, I came upon a project that I had built in the 80’s — an Automotive Multimeter which was published in the Dutch/British Elektor magazine. It could measure low voltage DC, high current DC, resistance, dwell angle, and engine RPM and ran off a single 9V battery. Besides a 555 IC for the dwell and RPM measurement and a couple of CMOS gate chips, the rest of the board is populated by a smattering of passives and a big, 40 pin DIP IC under the 3½ digit LCD display. I dug some more in my box, and came up with another Elektor project from back then — a True RMS digital Wattmeter with a 3½ digit LCD display that could measure up to 2kW. It had the same chip too. Some more digging, and I found a digital panel meter. This had a 7 segment LED display, but the chip was again from the same family.

ICL7107 LED version
ICL7107 LED version

Look under the hood of any device with a 3½ or 4½ digit, 7 segment, LCD or LED from the ’80’s or ’90’s and you will likely spot this 40-pin DIP with the Intersil logo (although it was later also manufactured by many other fabs; Harris and Maxim among others). The chip doing all the heavy-lifting was likely to be the ICL7106 or ICL7107. These devices were described as high performance, low power, 3½ digit A/D converters containing seven segment decoders, display drivers, voltage reference and clock. In short, everything you needed to take a DC analog signal and display it. Over time, a whole series of devices were spawned:

  • 7106 – 3½ digit, 7 segment LCD
  • 7107 – 3½ digit, 7 segment LED
  • 7116 – 3½ digit, 7 segment LCD, with display HOLD (freeze)
  • 7117 – 3½ digit, 7 segment LED, with display HOLD (freeze)
  • 7126 – improved 7106
  • 7136 – improved 7126
  • 7135 – 4½ digit, 7 segment LCD

There were many similar devices available, but the ICL71xx series was by far one of the most popular, due to its easy of use, low parts count and single chip implementation. Here are several parts (linking to PDF datasheets) to illustrate my point: the TC14433/A needed several peripheral devices, ES5107 (a clone of a clone — read below), CA3162 (which has BCD output, and needs the CA3161 or similar to interface to a display), or the AD2020 (which too needed a lot of support circuitry).

The ICL71xx was the go-to device for a reason. Let’s take a look at the engineering and business behind this fascinating chip.

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Understanding The Quartz Crystal Resonator

Accurate timing is one of the most basic requirements for so much of the technology we take for granted, yet how many of us pause to consider the component that enables us to have it? The quartz crystal is our go-to standard when we need an affordable, known, and stable clock frequency for our microprocessors and other digital circuits. Perhaps it’s time we took a closer look at it.

The first electronic oscillators at radio frequencies relied on the electrical properties of tuned circuits featuring inductors and capacitors to keep them on-frequency. Tuned circuits are cheap and easy to produce, however their frequency stability is extremely affected by external factors such as temperature and vibration. Thus an RF oscillator using a tuned circuit can drift by many kHz over the period of its operation, and its timing can not be relied upon. Long before accurate timing was needed for computers, the radio transmitters of the 1920s and 1930s needed to stay on frequency, and considerable effort had to be maintained to keep a tuned-circuit transmitter on-target. The quartz crystal was waiting to swoop in and save us this effort.

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Review: Hammer-Installed Solderless Raspberry Pi Pin Headers

A few days ago we reported on a new product for owners of the Raspberry Pi Zero, a set of solderless header pins that had a novel installation method involving a hammer. We were skeptical that they would provide a good contact, and preferred to stick with the tried-and-trusted soldered pins. It seems a lot of you agreed, and the comments section of the post became a little boisterous. Pimoroni, the originator of the product, came in for a lot of flak, with which to give them their due they engaged with good humor.

It’s obvious this was a controversial product, and maybe the Hackaday verdict had been a little summary based on the hammer aspect of the story. So to get further into what all the fuss had been about I ordered a Pi Zero and the solderless pin kit to try for ourselves.

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A Ten Turn Pot, For Not A Lot

If you have a traditional regulated power supply that you want to make adjustable, you’ll have somewhere in the circuit a feedback line driven by a potential divider across the output. That divider will probably incorporate a variable resistor, which you’ll adjust to select your desired voltage.

The problem with using a standard pot to adjust something like a power supply is that a large voltage range is spread across a relatively small angle. The tiniest movement of the shaft results in too large a voltage change for real fine-tuning, so clearly a better means of adjustment is called for. And in many cases that need is satisfied with a ten-turn potentiometer, simply a pot with a 10 to 1 reduction drive built-in.

[Dardo] had just this problem, and since 10-turn pots are expensive to buy and expensive to ship to his part of the world he built his own instead of buying one.

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New Part Day: Better Pins

If you’re making a circuit that is designed to plug into a breadboard, you have a problem. Those 0.1″ header pins are square, and the metal leaf contacts inside a solderless breadboard will eventually get bent out of shape. You only need to look at the breadboards in a university electronics lab for evidence of this.

The solution to this problem is to make pins that are as similar as possible to the leads on DIP chips. They should be flat, of course, and it would be nice if they didn’t have those plastic spacers and didn’t present a blob of solder on the top side of the chip.

Flip-Pins are the answer. Think of them as standard pin headers, but meant for breadboard applications, and having a great aesthetic for your projects. They’re designed to look as much like standard IC pins as possible, and have the same thickness (0.020″) as standard DIP leads.

The application of Flip-Pins is a lot like soldering standard 0.1″ pin headers. The pins ship in neat little plastic retainers and can be tacked onto a PCB with just a little bit of solder. There’s a datasheet, and models for Altium, KiCad, and Eagle.

Flip-Pins grew out of another project, the OSHChip, to create an all-in-wonder chip containing an ARM microcontroller, radio, and a crossbar so any pin can be mapped to any peripheral. The OSChip itself is very cool, but one question constantly asked of the creator of this neat chip was, ‘where did you get those pins?’ From a factory. Now you can buy these pins from Evil Mad Scientist and Tindie. They’re a bit pricey, but they do look great.

Diodes: The Switch You Never Knew You Had

Vishay's take on the 1N4148 data sheet (PDF), describing it as a switching diode.
Vishay’s take on the 1N4148 data sheet (PDF), describing it as a switching diode.

When looking across the discrete components in your electronic armory, it is easy to overlook the humble diode. After all, one can be forgiven for the conclusion that the everyday version of this component doesn’t do much. They have none of the special skills you’d find in tunnel, Gunn, varicap, Zener, and avalanche diodes, or even LEDs, instead they are simply a one-way valve for electrical current. Connect them one way round and current flows, the other and it doesn’t. They rectify AC to DC, power supplies are full of them. Perhaps you’ve also used them to generate a stable voltage drop because they have a pretty constant voltage across them when current is flowing, but that’s it. Diodes: the shortest Hackaday article ever.

Not so fast with dismissing the diode though. There is another trick they have hiding up their sleeves, they can also act as a switch. It shouldn’t come as too much of a shock, after all a quick look at many datasheets for general purpose diodes should reveal their description as switching diodes.

So how does a diode switch work? The key lies in that one-way valve we mentioned earlier. When the diode is forward biased and conducting electricity it will pass through any variations in the voltage being put into them, but when it is reverse biased and not conducting any electricity it will not. Thus a signal can be switched on by passing it through a diode in forward bias, and then turned off by putting the diode into reverse bias.

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