We’re surrounded by interesting engineering, but some of it is sealed inside a housing, away from easy inspection. A case in point; the humble gas regulator. It’s in equipment all around us, from a propane grill to welding gear. It’s a sealed unit — have you ever seen the inside, to know how it really works? Well thanks to [FarmCraft101], we get to do just that, in the video after the break.
To let the cat out of the bag, it’s essentially a hydraulic lever. A large diaphragm is pressurized by the low pressure side of the regulator, and is held back by a spring. When the pressure compared to ambient atmosphere is high enough to overcome the spring tension, the lever is tilted, closing the high pressure valve. Hence, pressure is determined by spring strength. We also get a look at how the system can fail — in this case it seemed to be some grit interfering with the valve. We find hidden engineering to be supremely satisfying, particularly when we get to understand it so clearly as we do here. Enjoy!
Continue reading “Seeing Inside A Gas Regulator”
Good news this morning from low Earth orbit, where the Hubble Space Telescope is back online after a long and worrisome month of inactivity following a glitch with the observatory’s payload computer.
We recently covered the Hubble payload computer in some depth; at the time, NASA was still very much in the diagnosis phase of the recovery, and had yet to determine a root cause. But the investigation was pointing to one of two possible culprits: the Command Unit/Science Data Formatter (CU/SDF), the module that interfaces the various science instruments, or the Power Control Unit (PCU), which provides regulated power for everything in the payload computer, more verbosely known as the SI C&DH, or Scientific Instrument Command and Data Handling Unit.
In the two weeks since that report, NASA made slow but steady progress, methodically testing every aspect of the SI C&DH. It wasn’t until just two days ago, on July 14, that NASA made a solid determination on root cause: the Power Control Unit, or more specifically, the power supply protection circuit on the PCU’s 5-volt rail. The circuit is designed to monitor the rail for undervoltage or overvoltage conditions, and to order the SI C&DH to shut down if the voltage is out of spec. It’s not entirely clear whether the PCU is actually putting out something other than 5 volts, or if the protection circuit has perhaps degraded since the entire SI C&DH was replaced in the last service mission in 2009. But either way, the fix is the same: switch to the backup PCU, a step that was carefully planned out and executed on July 15th.
To their credit, the agency took pains that everyone involved would be free from any sense of pressure to rush a fix — the 30-year-old spacecraft was stable, its instruments were all safely shut down, and so the imperative was to fix the problem without causing any collateral damage, or taking a step that couldn’t be undone. And further kudos go to NASA for transparency — the web page detailing their efforts to save Hubble reads almost like a build log on one of our projects.
There’s still quite a bit of work to be done to get Hubble back into business — the science instruments have to be woken up and checked out, for instance — but if all goes well, we should see science data start flowing back from the space telescope soon. It’s a relief that NASA was able to pull this fix off, but the fact that Hubble is down to its last backup is a reminder Hubble’s days are numbered, and that the best way to honor the feats of engineering derring-do that saved Hubble this time and many times before is to keep doing great science for as long as possible.
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.
[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.
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.
[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”
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.