See the Fabulous Workmanship in this Smart Pressure Regulator

For many projects that require control of air pressure, the usual option is to hook up a pump, maybe with a motor controller to turn it on and off, and work with that. If one’s requirements can’t be filled by that level of equipment and control, then it’s time to look at commercial regulators. [Craig Watson] did exactly that, but found the results as disappointing as they were expensive. He found that commercial offerings — especially at low pressures — tended to leak air, occasionally reported incorrect pressures, and in general just weren’t very precise. Out of a sense of necessity he set out to design his own electronically controlled, closed-loop pressure regulator. The metal block is a custom manifold with valve hardware mounted onto it, and the PCB mounted on top holds the control system. The project logs have some great pictures and details of the prototyping and fabrication process.

This project was the result of [Craig]’s work on a microfluidics control system, conceived because he discovered that much of the equipment involved in these useful systems is prohibitively expensive for small labs or individuals. In the course of developing the electronic pressure regulator, he realized it could have applications beyond microfluidics control, and created it as a modular device that can easily be integrated into other systems and handle either positive or negative pressure. It’s especially well-suited for anything with low air requirements and a limited supply, but with a need for precise control.

Fail Of The Week: Never Trust A Regulator Module

[Ryan Wamsley] has spent a lot of time over the past few months working on a new project, the Ultimate LoRa backplane. This is as its name suggests designed for LoRa wireless gateways, and packs in all the features he’d like to see in a LoRa expansion for the Nano Pi Duo.

His design features a three-terminal regulator, and in the quest for a bit more power efficiency he did what no doubt many of you will have done, and gave one of those little switching regulator modules in a three-terminal footprint a go. As part of his testing he inadvertently touched the regulator, and was instantly rewarded with a puff of smoke from his Nano Pi Duo. As it turned out, the regulator was susceptible to electrical noise, and had a fault condition in which its input voltage was routed directly to its output. As a result, a component in the single board computer received way more than its fair share, and burned out.

If there is a moral to be extracted from this story, it is to never fully trust a cheap drop-in module to behave exactly as its manufacturer claims. [Ryan]’s LoRa board lives to fight another day, but the smoke could so easily have come from more components.

So that’s the Fail of The Week part of this write-up complete, but it would be incomplete without the corresponding massive win that is [Ryan]’s LoRa board itself. Make sure to take a look at it, it’s a design into which a lot of attention to detail has been put.

Making A Classic Chip From Discretes

A hackspace discussion of voltage regulators within our earshot touched on the famous μA723, then moved on to its competitors. Kits-of-parts for linear regulators were ten-a-penny in the 1970s, it seems. A rambling tale ensued, involving a Lambda power supply with a blown-up chip, and ended up with a Google search for the unit in question. What it turned up was a hack from 2014 that somehow Hackaday missed at the time, the replication by [Eric Schlaepfer] of an out-of-production regulator chip using surface-mount semiconductors when his Lambda PSU expired.

Lambda were one of those annoying electronics companies with a habit of applying their own part numbers to commonly available chips in an effort to preserve their spares sales. Thus the FBT-031 in this Lambda PSU was in fact a Motorola MC1466, a dirt-cheap common part in the 1970s. Unfortunately though unlike the 723 the MC1466 has long passed out of production, and is rarer than the proverbial hen’s tooth.

Happily, these chips from the early 1970s were often surprisingly simple inside. The MC1466 schematic can be found on its data sheet, and is straightforward enough to replicate with surface-mount discrete components. He thus created a PCB that replicated the original pin layout even though it overlapped the original footprint. A few parts were slightly unusual, dual transistor arrays and a matched triple diode, but the result proved to be a perfect replacement for a real MC1466. Of course a project like this is almost too simple for [Eric], who went on to build the incredible Monster 6502.

If the data sheet lacks a schematic, never fear. You can always try reverse engineering the chip directly.

Circuit Challenge: Two Transistor 3.3V Regulator

[Kevin Darrah] wanted to make a simple 3.3V regulator without using an integrated circuit. He wound up using two common NPN transistors and 4 1K resistors. The circuit isn’t going to beat out a cheap linear regulator IC, but for the low component count, it is actually pretty good.

In all fairness, though, [Kevin] may have two transistors, but he’s only using one of them as a proper transistor. That one is a conventional pass regulator like you might find in any regulator circuit. The other transistor only has two connections. The design reverse biases the base-emitter junction which results in a roughly 8V breakdown voltage. Essentially, this transistor is being used as a poor-quality Zener diode.

Continue reading “Circuit Challenge: Two Transistor 3.3V Regulator”

Not Your Typical ATX Bench PSU

We know what you’re thinking — yet another scrap PC power supply turned into a bench PSU. But look a little closer and you’ll see a nicely designed linear bench supply that just fits inside a gutted ATX case.

A lot of the items on [Medzik]’s BOM for this build are straight from the scrap bin. The aforementioned ATX supply case is one, as is the power transformer donated by a friend. Modules such as the 30V/2A regulator, the digital volt/ammeter, and a thermostat module to control the fan at higher power settings were all sourced via the usual suspects. The PSU boasts two outputs — an adjustable 0-22 volt supply, and a fixed 12-volt output. An unusual design feature is a secondary input which uses the 22-VAC supply from a Weller soldering station to give the PSU a little more oomph. This boosts the maximum output to 30 volts; one wonders why [Medzik] didn’t just source a bigger transformer, but you work with what you have sometimes. There are some nice touches, too, like custom-printed vinyl overlays for the case.

It’s a good-looking and compact unit with a decent suite of features, and you could do a lot worse when building your next bench supply. If it’s not your cup of tea though, just take your pick — tiny and yellow, built to last, or ensconced in Ultrasuede.

A Lesson On Zener Regulators

For the longest time, Zener diode regulators have been one of those circuits that have been widely shared and highly misunderstood. First timers have tried to use it to power up their experiments and wondered why things did not go as planned. [James Lewis] has put up a worth tutorial on the subject titled, “Zener Diode makes for a Lousy Regulator”  that clarifies the misconceptions behind using the device.

[James Lewis] does an experiment with a regulator circuit with an ESP8266 after a short introduction to Zener diodes themselves. For the uninitiated, the Zener diode can operate in the reverse bias safely and can do so at a particular voltage. This allows for the voltage across the device to be a fixed value.

This, however, depends on the current flowing through the circuit which in turn relies on the load. The circuit will work as expected for loads the draw a small amount of current. This makes it suitable for generating reference voltages for microcontrollers and such.

To make a Zener into a “proper” voltage regulator, you just need to buffer the output with an amplifier of some kind. A single transistor is the bare minimum, but actually can work pretty well. You might also add a capacitor in parallel with the Zener to smooth out some of its noise.

Zener diodes are wonderful little devices and write-ups like these are indispensable for beginners and should be shared more often like the Zener and Schottky Tutorial and Diodes as a Switch.


Current Sink Keeps The Smoke In

One of the most versatile tools on anyone’s work bench, at least as far as electrical projects are concerned, is a power supply. Often we build our own, but after we’ve cobbled together some banana jacks with a computer’s PSU or dead-bug soldered a LM317 voltage regulator to a wall wart, how will that power supply perform? Since it’s not desirable to use a power supply that’ll let the smoke out of everything it powers (or itself, for that matter) a constant current sink, or load, can help determine the operating limits of the power supply.

[electrobob] built this particular current sink from parts he had lying around. The theory of a constant current sink is relatively straightforward so it’s easily possible to build one from parts out of the junk drawer, provided you can find a few transistors, fuses, an op amp, and some heat sinks. The full set of schematics that [electrobob] designed can be found on his main project page. He’s also gone a step further with this build as well, since he shorted out his first prototype and destroyed some of the transistors. But, using a few extra transistors in his design also improves the safety and performance of the load, so it’s a win-win.

This constant current load also has the added feature of being able to interface with a waveform generator (an Analog Discovery, specifically) and as a result can connect and disconnect the load quickly. If you aren’t in need of an industrial-grade constant current sink and you have some spare parts lying around, this would be a great one to have around the work bench.