Every once in a while we get wind of a project that we’re reluctant to write up for the simple reason that it looks too good to be true. Not that projects need to be messy to be authentic, mind you, but there are some that are just so finished and professional looking that it gives us a bit of pause. [Sebastian]’s programmable precision resistor is a shining example of such a project
While [Sebastian] describes this as “a glorified decade resistance box,” and technically that’s exactly right — at its heart it’s just a bunch of precision resistors being switched into networks to achieve a specific overall resistance — there’s a lot more going on here than just that. The project write-up, which has been rolling out slowly over the last month or so, has a lot of detail on different topologies that could have been used — [Sebastian] settled on a switched series network that only requires six relays per decade while also minimizing the contribution of relay contact resistance to the network. Speaking of which, there’s a detailed discussion on that subject, plus temperature compensation, power ratings, and how the various decades are linked together.
For as much that’s interesting about what’s under the hood, we’d be remiss to not spend a little time praising the exterior of this instrument. [Sebastian] appears to have spared no expense to make this look like a commercial product, from the rack-mount enclosure to the HP-esque front panel. The UI is all discrete pushbuttons and knobs with a long string of 16-segment LEDs — no fancy touch-screens here. The panel layout isn’t overly busy, and looks like it would be easy to use with some practice. We’d love to hear how the front and rear panel overlays were designed, too; maybe in a future project update.
This honestly looks like an instrument that you’d pay a princely sum to Keithley or H-P to own, at least back in the late 1990s or so. Kudos to [Sebastian] for the attention to detail here.
Well, we guess it had to happen eventually — Ford is putting plans in place to make its vehicles capable of self-repossession. At least it seems so from a patent application that was published last week, which reads like something written by someone who fancies themselves an evil genius but is just really, really annoying. Like most patent applications, it covers a lot of ground; aside from the obvious capability of a self-driving car to drive itself back to the dealership, Ford lists a number of steps that its proposed system could take before or instead of driving the car away from someone who’s behind on payments.
Examples include selective disabling conveniences in the vehicle, like the HVAC or infotainment systems, or even locking the doors and effectively bricking the vehicle. Ford graciously makes allowance for using the repossessed vehicle in an emergency, and makes mention of using cameras in the vehicle and a “neural network” to verify that the locked-out user is indeed having, say, a medical emergency. What could possibly go wrong?
It always fascinates us that every single thing that is made had to be designed by someone. Even something as simple as a bag and box that holds cereal. Someone had to work out the dimensions, the materials, the printing on it, and assign it a UPC code. Those people aren’t always engineers, but someone has to think it out no matter how mundane it is before it can be made. But what about the terms we use to express things? Someone has to work those out, too. In the case of metric prefixes like kilo, mega, and pico, it is apparently the General Conference on Weights and Measures that recently had its 27th session. As a result of that, we have four more metric prefixes to learn: ronna, quetta, ronto, and quecto.
Apparently, the new prefixes are to accommodate “big data” which is rapidly producing more data than there are atoms in the Universe. There were actually proposed earlier in a slightly different form but accepted at the conference. Apparently quecca is too close to a Portuguese swear word. So what do these actually mean? A QB (quettabyte) would be 1030 bytes while an RB (ronnabyte) is only 1027. So 1 QB would be 1,000,000 yottabytes (YB) the previous top of the scale.
A couple of years ago we published a look at precision measurement tools, in particular vernier calipers and micrometer screw gauges. It featured a look at how they work and how they’re used, and a comparison of good and bad quality instruments. When comparing micrometers we had three of them, a Mitutoyo and a Moore & Wright representing decent quality, and an £8 ($9.41) Daniu from Banggood from the cheaper end of the market. As you might expect, the Daniu was laughably bad, with noticeable play in its thread and jaws that were not parallel to the extent you could see light between them. You might consider it case closed for cheap micrometers then, were it not that while on my summer travels through the Benelux countries I spied a Parkside micrometer in a Lidl supermarket for €8.99 ($8.92). I had to buy it and investigate.
Some Measuring Devices With Your Groceries?
Lidl is a German supermarket chain that can be found all over Europe, and like their arch-competitor Aldi they feature the “Middle of Lidl” aisles full of all sorts of useful stuff that changes on a regular basis. Among this is a comprehensive range of tools under the Parkside brand, which is basically on par with the good stuff from Harbor Freight, and are in fact quite good for the price. Thus even though it’s about the same price as the Daniu I had higher expectations for the Parkside micrometer.
The micrometer is packaged in the usual plastic case in a small cardboard box, and comes with a large paper instruction sheet and a small spanner for zero adjustment. Taking it out of the case, it follows exactly as you’d expect from a micrometer with a solid drop-forged frame and an aluminium barrel on the micrometer head. It can measure up to 25 mm at a resolution of 0.01 mm, exactly like the others I tested in 2020. So my nine dollars or so has got me a micrometer, but is it any good? How do you evaluate a micrometer screw gauge? I re-borrowed the two comparison instruments from 2020, and set out to find out.
The Tiniest Sliver Of Light Gives It Away
The mirror finish on the Mitutoyo jaw face reflecting the “H” of the Hackaday website.
It’s worth saying that the jaw faces are polished, but not to a mirror finish as those on the Mitutoyo and neither do they appear to have been hardened. In the first instance, comparing with the Daniu I closed the jaws against the force of the ratchet, and held it up against the light to spot any imperfections in the way they meet. Against the blue sky through my window I couldn’t see any, but a friend did the same thing against the more intense point source of an electric light and indeed there was the tiniest discernable sliver of light. Not the obvious wedge of light I caught with the Daniu back in 2020 and less than the visible sliver of light when it is measuring a human hair, but definitely enough to knock a few hundredths of a milimetre off my trust in its accuracy.
The next step in the evaluation involves opening the jaws about half way, and feeling for any play in the thread. None discernable, at least one win over the Daniu which had the barrel flapping around with significant play. Then a zero test, after adjusting the zero position with the spanner a few repeated closings with the ratchet, to check that it always returns to the same zero point. In this case as with all micrometers it’s possible to overshoot the zero and damage the thread if you apply too much force, but just on the ratchet it would land in the same place. A pass on a couple of tests then, so while it’s not the worst micrometer ever it’s obvious that the low price brings at least one compromise.
A Tiny Discrepancy In Measurement
Opening up the three micrometers from the 2020 piece again it’s immediately obvious in the silky feel of the thread and the lack of wobble in the ratchet just where the money goes in an expensive micrometer, and just how comedically bad the Daniu was by comparison. But it’s the Parkside in our sights today, so it’s time to make a few comparitive measurements between it and the Mitutoyo. First up were the old standbys of a piece of paper and a human hair in which the Parkside returned the same as the Mitutoyo, and then the machined shaft of the Moore & Wright which returned a difference of 0.01 mm.
Parkside
Mitutoyo
Sheet of paper
0.12 mm
0.12 mm
Human hair
0.05 mm
0.05 mm
Moore & Wright shaft
6.79 mm
6.80 mm
The discrepancy in this table when measuring the shaft may be small, but it harks back to that sliver of light from imperfectly aligned jaws. As expected if the shaft meets the jaws at anything but the highest point of the jaw it will return a slightly smaller reading, thus it immediately has an error on everything it returns. Discussing it with friends there was raised the intriguing possibility of lapping the faces by drawing a sheet of exceptionally fine abrasive through the closed jaws, however I have my doubts as to whether this would do anything but make the gap worse.
What I can say about the Parkside micrometer screw gauge is that it appears reasonably well-built, but I can’t present it as the equal of the more expensive instruments when its faces are anything but parallel. I would say therefore that it would be good for basic measurements when machining or in CAD work where an error of 0.01 mm or 0.02 mm wouldn’t matter too much, but perhaps I wouldn’t quite trust it when working with extremely fine tolerances. Still, it’s not the worst among cheap micrometers and it’s on sale for a very reasonable price even if it’s not in the same precision instrument league as the Mitutoyo. If you don’t have a micrometer screw gauge yet then you could do a lot worse at this end of the market.
You may have seen surveyors (or maths students) running around with measuring wheels, counting the clicks to measure distances. [AGBarber]’s digital measuring wheel works in much the same way, but with the convenience of a measurement you can read off a screen.
The design is simple, and relies on the outer wheel of the device turning a mouse encoder wheel. This is read by anArduino Pro Mini which runs the show and records the requisite measurements. It then drives an SSD1306 OLED display which shows the measurements to the user. It’s all wrapped up in a 3D printed housing that makes it easy to roll around the small handheld device.
The wheel’s maximum measuring length is 9999.99 cm, or just under 100 meters. Given the size of the device, that’s probably more than enough, but you could always build a bigger version if you wanted to measure longer distances.
A lamp used to be simple thing: just stick a filament in a glass bulb, pass a current through it and behold! Let there be light. A bigger lamp meant a larger filament, taking more power and a larger envelope. Now we’ve moved on a bit, and it’s all about LEDs. There really isn’t such a thing as ‘just an LED,’ these are semiconductor devices, made from relatively exotic materials (OK, not just plain old silicon anyway) and there is quite a lot of variety to choose from, and a bit of complexity in selecting them.
For [Torque Test Channel] the efficiency of conversion from electrical power to radiant power (or flux) is the headline figure of interest, which prompted them to buy a bunch of lamps to compare. To do the job justice that requires what’s known in the business as an integrating sphere (aka an Ulbricht sphere), but being a specialist device, it’s a bit pricey for the home gamer. So naturally, they decided to build the thing themselves.
Coating the inside of the foam sphere took several attempts.
Firstly they did the sensible thing, and shipped off their test units to a metrology lab with the ‘proper’ equipment, to get a baseline to calibrate against. Next they set about using some fairly common materials to construct their sphere. The basic idea is quite simple; it has a uniform diffuse internal surface, which ensures that all photons emitted by a source can be measured at the appropriate measurement port, regardless of the angle they are emitted from the source. This way, the total radiated power can be determined, or at least estimated, since there will be a degree of absorption.
Anyway, after a couple of false starts with coating the internal surface, they came to the conclusion that mixing barium sulphate into the paint, and then a bit of a rub-down with sandpaper, gave the required pure white, diffuse surface.
The results from their testing, using a lux meter inserted into one of the other ports, showed a pretty good correspondence between their measured lux figure and the lab-determined lumens figure. Since one lux is defined as one lumen per square meter, they seemed to get lucky and found a consistent ten-to-one ratio between their observed value and the lab. This factor will be simply due to the physical setup of their contraption, but an encouraging result so far anyway. And what about the bottom line? Did those test units deliver their promised lumen output? It would seem that they pretty much did.
After pulling late hours in my school machine shop for a few years, I couldn’t help but wonder, who measures the measurement tools? How did they come to be? I’d heard anecdotes from other students and engineers while they inspected my freshly machined parts, but these stories were one-offs. What I wanted was a tale of industrial precision from start to finish. Years later, I found it.
The story of precision, as told by Simon Winchester, is captured in The Perfectionists: How Precision Engineers Created the Modern World. Published in 2018, Winchester’s overview stretches as far back to the Antikythera mechanism and brings us to present day silicon wafer manufacturing. Of course, this isn’t a chronology of all-things made precisely. Instead, it’s a romp through engineering highlights that hallmark either a certain level of precision manufacturing or a particular way of thinking with repercussions for the future. Continue reading “Books You Should Read: The Perfectionists”→
