[Ken] stepped up, and at first glance, it was obvious that most of the chip is unused, and there appeared to be four copies of the same circuit. After identifying resistors and the different transistor types, [Ken] found differential pairs.
Differential pairs form the heart of most op-amps, and by chaining them together, you can get a strong enough signal to treat it as a logic signal. Based on the design and materials, [Ken] estimates the chip is from the 1970s. Given that it appears to be ECL (Emitter-Coupled Logic), it could just be four comparators. But there are still a few things that don’t add up as two comparators have additional inverted outputs. Searching the part number offered few if any clues, so this will remain somewhat a mystery.
“You should have used a 555” has become a bit of a meme around these parts lately, and for good reason. There seems to be little that these ubiquitous chips can’t be used for, and in a world where code often substitutes for hardware, it’s easy to point to instances where one could have just used a simple timer chip instead.
Definitely not in the meme category, though, is this overkill vacuum tube 555 timer. It comes to us via [David Lovett], aka [Usagi Electric], who has lately caught the “hollow state” electronics bug and has been experimenting with all sorts of vacuum tube recreations of circuits we’re far more used to seeing rendered in silicon than glass. The urge to replicate the venerable 555 in nothing but vacuum tubes is understandable, as it uses little more than a pair of comparators and a flip-flop, circuits [David] has already built vacuum tube versions of. The only part left was the discharge transistor; a pentode was enlisted to stand in for that vital function, making the circuit complete.
To physically implement the design, [David] built a large PCB to hold the 18 vacuum tubes and the handful of resistors and capacitors needed. Mounted on eight outsized leads made from sheet steel, the circuit pays homage to the original 8-pin DIP form of the 555. The video below shows the design and build process as well as testing of all the common modes of operation for the timer chip.
When you need a continuity tester at the bench, what do you reach for? Probably your multimeter, right? It may surprise you to know that the continuity tester in the meter isn’t all that sensitive, even if it’s the yellow expensive kind. [Leo]’s will beep even if there is 50Ω of resistance in the line.
There’s no power switch or even labels, because it doesn’t need any. Just put the probes where you want ’em, and it either beeps and lights the LED or it doesn’t. It looks simple, but inside that blast-resistant enclosure are lots of cool features that certainly make it seem like the ideal tester to us.
Our favorite has to be the transient blocking unit that works like a little circuit breaker. They’re used to protect circuits from lighting and electrostatic discharge by way of depletion-mode MOSFETs and switches to protected mode in under a microsecond. Watch [Leo] build this workbench necessity and then abuse test it with mains power after the break.
LEDs weren’t always an easy solution to displays and indicators. The fine folks at [Industrial Alchemy] shared pictures of a device that shows what kind of effort and cost went into making a high brightness bar graph display in the 70s, back when LEDs were both expensive and not particularly bright. There are no strange materials or methods involved in making the display daylight-readable, but it’s a peek at how solving problems we take for granted today sometimes took a lot of expense and effort.
The display is a row of 28 small incandescent bulbs, mounted in a PCB and housed in a machined aluminum frame. Holes through which to view the bulbs are on both the top and front of the metal housing, which allows the unit to be mounted in different orientations. It was made as a swappable module, its 56 machined gold pins mate to sockets on the driver board. The driver board itself consists of 14 LM119 dual comparators, each of which controls two bulbs on the display.
[Industrial Alchemy] believes that the display unit itself may have been a bit of a hack in its own way. Based on the pin spacing and dimensions of the driver board, they feel that it was probably designed to host a row of modular units known as the Wamco minitron bar graph display. An example is pictured here; they resembled DIP chips and could be stacked side-by-side to make a display of any length. Each window contained an incandescent filament in a reflective well, and each light could be individually controlled.
These minitron bar graph units could only be viewed from the top, and were apparently high in cost and low in availability. Getting around these limitations may have been worth creating this compatible unit despite the work involved.
Display technology has taken many different turns over the years, and you can see examples of many of them in one place in the Circus Clock, which tells the time with a different technology for each digit: a nixie, a numitron, a 7-segment thyratron tube, a VFD, an LED dot display, and a rear projection display.
Regular readers may recall we recently covered a neat Arduino trick that allowed you to “blow out” an LED as if it was a candle. The idea was that the LED itself could be used as a rudimentary temperature sensor, and the Arduino code would turn the LED on and off when a change was detected in its forward voltage drop. You need to oversample the Arduino’s ADC to detect the few millivolt change reliably, but overall it’s pretty simple once you understand the principle.
Not to say it’s easy to replicate the original Arduino project with a 555, or that it’s even practical. [Andrzej] simply wanted to show it was possible, which is something we always respect around these parts. He goes into great detail on how he developed and tested the circuit, even including oscilloscope screenshots showing how the different components work together in real-time. But the short version is that a MOSFET is used to turn the LED on and off, a comparator detects change in the LED’s voltage drop, and the 555 is used to control how long the LED stays off for.
Isn’t it always the way? There’s a circuit right out of the textbooks, or even a chip designed to do exactly what you want — almost exactly. It’s 80% perfect for your application, and rather than accept that 20%, you decide to start from scratch and design your own solution.
That’s the position [Great Scott!] found himself in with this custom LED battery level indicator. As the video below unfolds we learn that he didn’t start exactly from scratch, though. His first pass was the entirely sensible use of the LM3914 10-LED bar graph driver chip, a device that’s been running VU meters and the like for the better part of four decades. With an internal ladder of comparators and 1-kilohm resistors, the chip lights up the 10 LEDs according to an input voltage relative to an upper and lower limit set by external resistors. Unfortunately, the fixed internal resistors make that a linear scale, which does not match the discharge curve of the battery pack he’s monitoring. So, taking design elements from the LM3914 datasheet, [Great Scott!] rolled his own six-LED display from LM324 quad-op amps. Rather than a fixed resistance for each stage, trimmers let him tweak the curve to match the battery, and now he knows the remaining battery life with greater confidence.
It never fails — we post a somewhat simple project using a microcontroller and someone points out that it could have been accomplished better with a 555 timer or discrete transistors or even a couple of vacuum tubes. We welcome the critiques, of course; after all, thoughtful feedback is the point of the comment section. Sometimes the anti-Arduino crowd has a point, but as [Great Scott!] demonstrates with this microcontroller-less boost converter, other times it just makes sense to code your way out of a problem.
Built mainly as a comeback to naysayers on his original boost-converter circuit, which relied on an ATtiny85, [Great Scott!] had to go to considerable lengths to recreate what he did with ease using a microcontroller. He started with a quick demo using a MOSFET driver and a PWM signal from a function generator, which does the job of boosting the voltage, but lacks the feedback needed to control for varying loads.
Ironically relying on a block diagram for a commercial boost controller chip, which is probably the “right” tool for the job he put together the final circuit from a largish handful of components. Two op amps form the oscillator, another is used as a differential amp to monitor the output voltage, and the last one is a used as a comparator to create the PWM signal to control the MOSFET. It works, to be sure, but at the cost of a lot of effort, expense, and perf board real estate. What’s worse, there’s no simple path to adding functionality, like there would be for a microcontroller-based design.
Of course there are circuits where microcontrollers make no sense, but [Great Scott!] makes a good case for boost converters not being one of them if you insist on DIYing. If you’re behind on the basics of DC-DC converters, fear not — we’ve covered that before.