Ask Hackaday: Help Me Choose A ‘Scope

If there is one instrument that makes an electronic engineer’s bench, it is the oscilloscope. The ability to track voltages in the time domain and measure their period and amplitude is one akin to a light in the darkness, it turns a mere tinkerer with circuits into one in command of them. Straightforward add-on circuits can transform a basic oscilloscope into a curve tracer, frequency response display, and much more, and modern oscilloscopes offer a dizzying array of useful measurement features unimaginable to engineers only a few years ago. And I need your help to pick a new one.

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Yet Another Inductance Measuring Scheme

How do you measure the value of an unknown inductor? If you have an LCR bridge or meter, you are probably going to use that. If not, there are many different techniques you can use. All of them rely on the same thing my Algebra teacher Mr. Harder used to say back in the 1970’s: you have to use what you know to get what you don’t know.

[Ronald Dekker] must think the same way. He took a 50-ohm signal generator and a scope. He puts the signal output to about 20kHz and adjusts for 1V peak-to-peak on the scope. Then he puts the unknown inductor across the signal and adjusts the frequency (and only the frequency) for an output of 1/2 volt peak-to-peak.

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[Alan Wolke]’s How To Use An Oscilloscope

If you were to create a Venn diagram of Hackaday readers and oscilloscope owners the chances are the there would be a very significant intersection of the two sets. Whether the instrument in question is a decades-old CRT workhorse or a shiny modern digital ‘scope, it’s probably something you’ll use pretty often and you’ll be very familiar with its operation.

An oscilloscope is a very complex instrument containing a huge number of features. Modern ‘scopes in particular bring capabilities through software unimaginable only a few years ago. So when you look at your ‘scope, do you really know how to use its every feature? Are you getting the best from it, or are you only scratching the surface of what it can do?

[Alan Wolke, W2AEW] is an application engineer at Tektronix, so as you might expect when it comes to oscilloscopes he knows a thing or two about them. He’s spoken on the subject in the past with his “Scopes for Dopes” lecture, and his latest video is a presentation to the NJ Antique Radio Club which is a very thorough exploration of using an oscilloscope. The video is below the break and at an hour and twenty minutes it’s a long one. We make no apologies for that, for it should be fascinating in its entirety for any oscilloscope owner. Even if you find yourself nodding along to most of what he’s saying there are sure to be pearls of ‘scope wisdom in there you weren’t aware of.

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Hackaday Links: July 17, 2016

There’s going to be a new Nintendo console for Christmas! It’s the NES Classic Edition. It looks like a minified NES, with weird connectors that look like the connector for the Wii Nunchuck. There are no other details.

A site called “Motherboard” reports assembling a computer is too hard and a ‘nerve-wrecking [sic]’ process. Tip of the stovepipe to the Totalbiscuit.

When I was in elementary school, the playground had a twenty foot tall metal slide that faced South. During my time there, at least three of my classmates fell off it, and I distinctly remember the school nurse’s aid running past me on the playground with a wheelchair. There wasn’t soft mulch or the weird rubber granules under this slide – just hard, compacted dirt. This slide was awesome, even if it was torn down when I was in third grade. [Brandon Hart]’s kid’s won’t look back fondly on their youth with experiences like these; he built a water-cooled slide in his backyard. He’s getting an 80°F ΔT with a trip to Ace Hardware, probably $20 in fittings, and a drill. Neat.

This is probably better suited for an ‘Ask Hackaday’ column, but [Arsenijs] has run into a bit of a problem with his Raspberry Pi Project. He’s trying to use a planarized kernel module to obfuscate the SPI bus, but he can’t do that because of a oblivated drumble pin. He could, of course, deenumerate several of the GISP modules, but this would cause a buffer underflow and eventually wreck the entire cloudstack. I told him he should use Corrosion, but he seems dead set on his Hokey implementation. If anyone has any ideas, get the glamphs and put it on the grumbo.

The Owon SDS7102 oscilloscope is a small, cheap, two-channel scope that is impressive for its price but noisier than you would expect. This scope has been thoroughly reverse engineered, and now Linux is running on this scope. This Linux scope has a working VGA display, USB host, USB device, Flash, and working Ethernet. The entire analog front end has been reversed engineered, and somehow this is now the most open oscilloscope you can buy.

The ESP32 is Espressif’s followup to their very popular ESP8266 WiFi module. The ESP32 will be much more powerful and include Bluetooth when it’s released in August. Until then, [Pighixxx] has the complete pinout for the ESP32.

Reverse Engineering The OWON SDS7102 Oscilloscope

It is something of a rite of passage for an electronics enthusiast, the acquisition of a first oscilloscope. In decades past that usually meant a relatively modest instrument, maybe a 20MHz bandwidth and dual trace if you were lucky. Higher spec devices were eye-wateringly expensive monsters, not for the Common People.

We are fortunate that like most other areas of technology the world of test equipment has benefited in the last few years both from developments in digital technology and from the growth in Chinese manufacturing. If your first ‘scope is that second-hand 20MHz CRT you will probably secure it for pennies, and the first ‘scope you buy new will probably have a spec closer to those unattainable super-scopes of yesteryear. Gone is the CRT and timebase generator, in its place a TFT, system-on-chip, and super-fast A to D converter.

[Christer Weinigel] has just such an entry-level modern digital ‘scope, an OWON SDS7102. He comments that it’s got an impressive spec for its price, though the input is noisier than you’d expect on a more expensive device, and the software has one or two annoying bugs. Having owned it for a while, he’s now subjected it to a lengthy teardown and reverse engineer, and he’s posted his findings in a succession of blog posts.

[Christer]’s interest lay mainly in the OWON’s digital section, it seems there is already a substantial community paying attention to its analog front end. He’s deduced how its internals are connected, ported Linux to its Samsung SoC in the scope, succeeded in getting its peripherals working, and set to work programming the Xilinx FPGA that’s responsible for signal processing.

The series of posts is a fascinating read as a run through the process of reverse engineering , but he points out that it’s quite a lot of information. If you are just interested in how a cheap modern oscilloscope works, he says, he suggests reading his post in which he recaps on all its different components.

He also makes a plea for help, he’s no slouch on the ‘scope’s software but admits he’s a bit out of his depth on some aspects of the FPGA. If you’re an FPGA wizard with an interest in ‘scopes, he’d like to hear from you.

This isn’t the first time we’ve featured ‘scope reverse engineering here at Hackaday, though it may be more in-depth than others. In the past we’ve seen a Uni-T screen grab protocol laid bare, and an investigation of a Rigol 1054Z.

Crowdfunding: A Wireless Oscilloscope

One of the most ingenious developments in test and measuring tools over the last few years is the Mooshimeter. That’s a wireless, two-channel multimeter that can measure voltage and current simultaneously. If you’ve ever wanted to look at the voltage drop and power output on a souped up electrified go-kart, the Mooshimeter is the tool for you.

A cheap, wireless multimeter was only the fevered dream of a madman a decade ago. We didn’t have smartphones with Bluetooth back then, so any remote display would cost much more than the multimeter itself. Now this test and measurement over Bluetooth is bleeding over into the rest of the electronics workbench with the Aeroscope,  a wireless Bluetooth oscilloscope.

[Alexander] and [Jonathan], the devs for the Aeroscope got the idea for this device while debugging a mobile robot. The robot would work on the bench, but in the field the problem would reappear. The idea for a wireless troubleshooting tool was born out of necessity.

The specs for the Aeroscope are about equal to the quite capable ‘My First Oscilloscope’ Rigol DS1052E. Analog bandwidth is 100MHz, sample rate is 500 Msamples/second, and the memory depth is 10k points. Resolution per division is 20mV to 10V, and the Aeroscope “Deluxe Package” that includes a few leads, tip, clip, USB cable, and case is about the same price as the Rigol 1052E. The difference, of course, is that the Aeroscope is a single channel, and wireless. That’s fairly impressive for two guys who aren’t a team of Rigol engineers.

As is the case with all Bluetooth test and measurement devices, the proof is in the app. Right now, the Aeroscope only supports iOS 9 devices, but according to the crowdfunding campaign, Android support is coming. Since the device is Open Source, you can always bang something out in Python if you really need to.

While this is a crowdfunding campaign, it’s hosted on Crowd Supply. Crowd Supply isn’t Indiegogo or Kickstarter; there are people at Crowd Supply vetting projects. The campaign still has a month to go, but the first few pledges are putting the Aeroscope right on track to a successful campaign.

Fixing a broken CCFL Backlight

When you work at Tektronix and they make a difficult to refuse offer for their ‘scopes, you obviously grab it. Even if the only one you can afford is the not-so-awesome TDS1012. [Jason Milldrum] got his unit before cheaper, and better ‘scopes appeared on the market. It served him well for quite a long time. But keeping it switched on all the time took a toll, and eventually the CCFL backlight failed. Here’s how he replaced the CCFL back light with a strip of LED’s and revived the instrument.

Searching for an original replacement CCFL backlight didn’t turn up anything – it had been obsoleted long back. Even his back-channel contacts in Tektronix couldn’t help him nor could he find anything on eBay. That’s when he came across a video by [Shahriar] who hosts the popular The Signal Path blog. It showed how the CCFL can be replaced by a thin strip of SMD LEDs powered by a DC-DC converter. [Jason] ordered out the parts needed, and having worked at Tektronix, knew exactly how to tear down the ‘scope. Maybe he was a bit rusty, as he ended up breaking some (non-critical) plastic tabs while removing the old CCFL. Nothing which could not be fixed with some silicone sealant.

The original DC-DC converter supplied along with his LED strip needed a 12V input, which was not available on the TDS1012. Instead of trying to hack that converter to work off 6V, he opted to order out another suitable converter instead. [Jason]’s blog details all the steps needed, peppered with lots of pictures, on how to make the swap. The one important caveat to be aware of is the effect of the LED DC-DC converter on the oscilloscope. Noise from the converter is likely to cause some performance issues, but that could be fixed by using a more expensive module with RF and EMI filtering.

This is not an original hack for sure. Here’s a “Laptop backlight converted from CCFL to LED” from a few years back, and this one for “LCD: Replacing CCFL with LEDs” from even further back in time. Hopefully if you have an instrument with a similar issue, these ought to guide you on how to fix things.