Homebrew Calibration For Test Equipment

June 15, 2018 by Al Williams 8 Comments

If you work for a large company, you probably have test equipment that is routinely calibrated. Some companies have their own metrology labs and others send out to an external lab. In a garage lab, you are less likely to do calibrations and — in our experience — that isn’t usually a problem. Still, it is nice to be able to do at least a sanity check on your gear. Also, if you buy old test gear and repair it, it would be nice to be able to check it, as well. [IMSAI guy] built his own little calibration setup, adding to it over the years, and he shares the details in a recent video, which you can see below.

The board started out simply as one voltage regulator and some 0.01% resistors. Over time, though, he added a few more bells and whistles. The setup isn’t going to rival a NIST-traceable lab setup, but for your garage it is perfectly fine.

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Drifting Instrument Presents Opportunity To Learn About Crystal Oscillators

June 5, 2018 by Dan Maloney 11 Comments

Sure, we all love fixing stuff, but there’s often a fine line between something that’s worth repairing and something that’s cheaper in the long run to just replace. That line gets blurred, though, when there’s something to be learned from a repair.

This wonky temperature-compensated crystal oscillator is a good example of leaning toward repair just for the opportunity to peek inside. [Kerry Wong] identified it as the problem behind a programmable frequency counter reading significantly low. A TCXO is supposed to output a fixed frequency signal that stays stable over a range of temperatures by using a temperature sensor to adjust a voltage-controlled oscillator that corrects for the crystal’s natural tendency to vary its frequency as it gets hotter or colder. But this TCXO was pretty old, and even the trimmer capacitor provided was no longer enough to nudge it back in range. [Kerry] did some Dremel surgery on the case and came to the conclusion that adding another trim cap between one of the crystal’s leads and ground would help. This gave him a much wider adjustment range and let him zero in on the correct 10-MHz setting. [Mr. Murphy] still runs the show, though – after he got the TCXO buttoned up with the new trimmer inaccessible, he found that the frequency was not quite right. But going from 2 kHz off to only 2 Hz is still pretty good.

Whether it’s the weird world of microwave electronics or building a whole-house battery bank, it’s always fun to watch [Kerry]’s videos, and we usually end up learning a thing or two.

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Characterizing A Cheap 500MHz Counter Module

November 16, 2016 by Jenny List 22 Comments

An exciting development over the last few years has been the arrival of extremely cheap instrumentation modules easily bought online and usually shipped from China. Some of them have extremely impressive paper specifications for their price, and it was one of these that caught the eye of [Carol Milazzo, KP4MD]. A frequency counter for under $14 on your favourite online retailer, and with a claimed range of 500 MHz. That could be a useful instrument in its own right, and with a range that significantly exceeds the capabilities of much more expensive bench test equipment from not so long ago.

Just how good is it though, does it live up to the promise? [Carol] presents the measurements she took from the device, so you can see for yourselves. She took look at sensitivity, VSWR, and input impedance over a wide range, after first checking its calibration against a GPS-disciplined standard and making a fine adjustment with its on-board trimmer.

In sensitivity terms it’s a bit deaf, requiring 0.11 Vrms for a lock at 10 MHz. Meanwhile its input impedance decreases from 600 ohms at the bottom of its range to 80 ohms at 200 MHz, with a corresponding shift in VSWR. So it’s never going to match a high-end bench instrument from which you’d expect much more sensitivity and a more stable impedance, but for the price we’re sure that’s something you can all work around. Meanwhile it’s worth noting from the pictures she’s posted that the board has unpopulated space for an SPI interface header, which leaves the potential for it to be used as a logging instrument.

We think it’s worth having as much information as possible about components like this one, both in terms of knowing about new entrants to the market and in knowing their true performance. So if you were curious about those cheap frequency counter modules, now thanks to [Carol] you have some idea of what they can do.

While it’s convenient to buy a counter module like this one, of course there is nothing to stop you building your own. We’ve featured many over the years, this 100MHz one using a 74-series prescaler or this ATtiny offering for example, or how about this very accomplished one with an Android UI?

3D Printer Tool: Set Your Extruder Steps With Ease

January 27, 2016 by Gerrit Coetzee 25 Comments

My printer has other issues that i'm still tuning out, but the warping in PLA and excessive surface roughness has all the signs of over extrusion. — My printer has other issues that I’m still tuning out, but the warping in PLA and excessive surface roughness has all the signs of over extrusion.

I have an old Prusa i2 that, like an old car, has been getting some major part replacements lately after many many hours of service. Recently both the extruder and the extruder motor died. The extruder died of brass fill filament sintering to the inside of the nozzle (always flush your extruder of exotic filaments). The motor died at the wires of constant flexing. Regardless, I replaced the motors and found myself with an issue; the new motor and hotend (junk motor from the junk bin, and an E3D v6, which is fantastic) worked way better and was pushing out too much filament.

The hotend, driver gear, extruder mechanics, back pressure, motor, and plastic type all work together to set how much plastic you can push through the nozzle at once. Even the speed at which the plastic is going through the nozzle can change how much friction that plastic experiences. Most of these effects are somewhat negligible. The printer does, however, have a sort of baseline steps per mm of plastic you can set.

The goal is to have a steps per mm that is exactly matched to how much plastic the printer pushes out. If you say 10mm, 10mm of filament should be eaten by the extruder. This setting is the “steps per mm” in the firmware configuration. This number should be close to perfect. Once it is, you can tune it by setting the “extrusion multiplier” setting in most slicers when you switch materials, or have environmental differences to compensate for.

This little guy lets you tune the steps per mm exactly.

The problem comes in measuring the filament that is extruded. Filament comes off a spool and is pulled through an imprecisely held nozzle in an imprecisely made extruder assembly. On top of all that, the filament twists and curves. This makes it difficult to hold against a ruler or caliper and get a trustworthy measurement.

I have come up with a little measuring device you can make with some brass tubing, sandpaper, a saw (or pipe cutter), a pencil torch, solder, and some calipers. To start with, find two pieces of tubing. The first’s ID must fit closely with the filament size you use. The second tube must allow the inside tubing to slide inside of it closely. A close fit is essential.

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Repair And Calibration Of Valhalla Programmable Precision Standard

January 25, 2016 by Anool Mahidharia 5 Comments

Precision standards are the pinnacle of test and measuring instrumentation. Well engineered, sure, but also beautifully built and a feast to look at, no matter how old they are. [Shahriar] at “The Signal Path” often gives us the skinny on such equipment. In the latest episode, we get a look inside a Valhalla 2701C Programmable Precision DC Voltage Standard.

Even by 1990 standards, it is a fairly basic instrument, capable of producing just DC Voltages from 100nV up to 1200V. But it is a reference standard, so the output is highly stable, accurate and precise. He snagged it from eBay on the cheap but transport seemed to have caused some damage. It would switch on and relays would click when he pressed buttons, but the 7-segment LED display was blank. Luckily, opening the top cover fixes that problem – just a loose connection between the front display and the main board. Examination also shows that adding a 120mA DC current range would require adding additional components on the main board so his hope of doing a quick firmware upgrade is short lived.

[Shahriar] takes the opportunity to walk us through the various sections of the well built unit. It’s apparently seen some repairs during it’s life. A few capacitors look changed, and a relay housing has seen damage from a soldering iron. The digital section is mainly the 6800 micro controller, an EPROM and a NVRAM, and it generates the PWM signals needed for producing the output voltages. A highly precise reference signal is essential for such equipment, and this one uses the LM299 with a “custom” suffix meaning it was specially screened and binned. He does a quick calibration run, but it’s obviously rushed and doesn’t produce stable results. But that could also be due to the low quality cables he used, or a number of other factors. Calibrating such equipment is a job demanding both time and patience.

While this may not knock your socks off. For that, check out this post where [Shahriar] does a tear down of the one million dollar Labmaster 10-100zi Oscilloscope, or this other one where he plays around with a half a million dollar oscilloscope you’ll probably never use, much less own.

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Hackaday Links: July 27, 2014

July 27, 2014 by Brian Benchoff 14 Comments

Taking apart printers to salvage their motors and rods is a common occurrence in hacker circles, but how about salvaging the electronics? A lot of printers come with WiFi modules, and these can be repurposed as USB WiFi dongles. Tools required? And old printer, 3.3 V regulator, and a USB cable. Couldn’t be simpler.

The Raspberry Pi has a connector for a webcam, and it’s a very good solution if you need a programmable IP webcam with GPIOs. How about four cameras?. This Indiegogo is for a four-port camera connector for the Raspi. Someone has a use for this, we’re sure.

The one flexible funding campaign that isn’t a scam. [Kyle] maintains most of the software defined radio stack for Arch Linux, and he’s looking for some funds to improve his work. Yes, it’s basically a ‘fund my life’ crowdfunding campaign, but you’re funding someone to work full-time on open source software.

Calibration tools for Delta 3D printers. It’s just a few tools that speed up calibration, made for MATLAB and Octave.

[Oona] is doing her usual, ‘lets look at everything radio’ thing again, and has a plan to map microwave relay links. If you’ve ever seen a dish or other highly directional antenna on top of a cell phone tower, you’ve seen this sort of thing before. [Oona] is planning on mapping them by flying a quadcopter around, extracting the video and GPS data, and figuring out where all the other microwave links are.

PowerPoint presentations for the Raspberry Pi and BeagleBone Black. Yes, PowerPoint presentations are the tool of the devil and the leading cause of death for astronauts*, but someone should find this useful.

* Yes, PowerPoint presentations are the leading cause of death for astronauts. The root cause of the Columbia disaster was organizational factors that neglected engineer’s requests to use DOD space assets to inspect the wing, after which they could have been rescued. These are organizational factors were, at least in part, caused by PowerPoint.

Challenger was the same story, and although PowerPoint didn’t exist in 1986, “bulletized thinking” in engineering reports was cited as a major factor in the disaster. If “bulletized thinking” doesn’t perfectly describe PowerPoint, I don’t know what does.

As far as PowerPoint being the leading cause of death for astronauts, 14 died on two shuttles, while a total of 30 astronauts died either in training or in flight.

Projector Calibration On Uneven Surfaces Made Easy

February 29, 2012 by Mike Nathan 18 Comments

projector-calibrator

If you are thinking of building your own flight/racing sim setup at home, you might want to check this out. [Alex] from the Garoa Hackerspace in Säo Paulo, Brazil put together a slick setup that makes projector image calibration a breeze.

When building a wraparound screen for such a simulator, you are likely to run into problems with both overlapping images and distortion from the curved projection. There are projectors that can easily adjust themselves to work in this sort of setup, but they are often very expensive, so [Alex] thought he would build a solution himself.

After studying a paper written by [Johnny Chung Lee] in 2004, he built a prototype display calibrator last year that used similar, though slightly tweaked methods to get the job done. This time around, [Alex] has improved his calibrator, making the process more precise and a bit quicker.

Light sensors and an Arduino are attached to the back of the projection medium, and a large broad scan of the screen is performed by the projector. His code then triggers an additional sweep of each corner to better estimate the exact edges of his projection surface. Since the video is tweaked in software rather than relying on the projector hardware to handle the task, the result is cheap and very accurate.

Don’t take our word for it though, check out [Alex’s] video demonstration below to see his calibrator in action.

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