OWON Oscilloscope Teardown

January 15, 2020 by Al Williams 27 Comments

We sympathize with [learnelectronic’s] statement: “I’m ashamed. I may have bought another oscilloscope.” We get it and we enjoyed watching him tear down the OWON SDS1102. (Video, embedded below.) As you might guess, this is a 100 MHz, two-channel scope, and very similar to many other Chinese scopes you can get inexpensively.

The last ten minutes are so of the video below shows him removing the case. There’s only three little boards inside. One is clearly a power supply. The other two don’t have much on them. There’s a tiny RF shield over one part of the board, so you assume that’s the input section.

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How To Design A Low Cost Probe-Oscilloscope

December 16, 2019 by Gerrit Coetzee 22 Comments

[Mark Omo] sends in his write up on the design of what should hopefully be a sub-$100 oscilloscope in a probe.

Many problems in engineering can be solved simply by throwing money at the them. It’s really when you start to apply constraints that the real innovation happens. The Probe-Scope Team’s vision is of a USB oscilloscope with 60MHz bandwidth and 25Msps. The cool twist is that by adding another probe to a free USB port on your computer you’re essentially adding a channel. By the time you get to four you’re at the same price as a normal oscilloscope but with an arguably more flexible set-up.

The project is also open source. When compared to popular oscilloscopes such as a Rigol it has pretty comparable performance considering how many components each channel on a discount scope usually share due to clever switching circuitry.

The probe is based around an Analog Devices ADC whose data is handled by a tag team of a Lattice FPGA and a 32bit PIC micro controller. You can see all the code and design files on their github. Their write-up contains a very thorough explanation of the circuitry. We hope they keep the project momentum going!

The Cutest Oscilloscope Ever Made

October 10, 2019 by Sharon Lin 11 Comments

If you thought your handheld digital oscilloscope was the most transportable of your signal analyzing tools, then you’re in for a surprise. This oscilloscope made by [Mark Omo] measures only one square inch, with the majority of the space taken up by the OLED screen.

It folds out into an easier instrument to hold, and admittedly does require external inputs, so it’s not exactly a standalone tool. The oscilloscope runs on a PIC32MZ EF processor, achieving 20Msps and 1MHz of bandwidth. The former interleaves the processor’s internal ADCs in order to achieve its speed.

For the analog front-end the signals first enter a 1M ohm terminator that divide the signals by 10x in order to measure them outside the rails. They then get passed through a pair of diodes connected to the rails, clamping the voltage to prevent damage. The divider centers the incoming AC signal around 1.65V, halfway between AGND and +3.3V. As a further safety feature, a larger 909k Ohm resistor sits between the signals and the diodes in order to prevent a large current from passing through the diode in the event of a large voltage entering the system.

The next component is a variable gain stage, providing either 10x, 5x, or 1x gain corresponding to 1x, 0.5x, and 0.1x system gains. For the subsystem, a TLV3541 op-amp and ADG633 tripe SPDT analog switch are used to provide a power bandwidth around the system response due to driving concerns. Notably, the resistance of the switch is non-negligible, potentially varying with voltage. Luckily, the screen used in the oscilloscope needs 12V, so supplying 12V to the mux results in a lower voltage and thus a flatter response.

The ADC module, PIC32MZ1024EFH064, is a 12-bit successive approximation ADC. One advantage of his particular ADC is that extra bits of resolution only take constant time, so speed and accuracy can be traded off. The conversion starts with a sample and hold sequence, using stored voltage on the capacitor to calculate the voltage.

Several ADCs are used in parallel to sample at the same time, resulting in the interleaving improving the sample rate. Since there are 120 Megabits per second of data coming from the ADC module, the Direct Memory Access (DMA) peripheral on the PIC32MZ allows for the writing of the data directly onto the memory of the microcontroller without involving the processor.

The firmware is currently available on GitHub and the schematics are published on the project page.

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You Don’t Need That Bulky CRT Oscilloscope Anymore

June 5, 2019 by Bryan Cockfield 92 Comments

While it might be nice to use a $4,000 oscilloscope in a lab at a university or well-funded corporate environment, a good portion of us won’t have access to that kind of equipment in our own home shops. There are a few ways of getting a working oscilloscope without breaking the bank, though. One option is to find old CRT-based unit for maybe $50 on craigslist which might still have 60% of its original 1970s-era equipment still operational. A more reliable, and similarly-priced, way of getting an oscilloscope is to just convert a device you already have.

The EspoTek Labrador is an open-source way of converting a Raspberry Pi, Android device, or even a regular run-of-the-mill computer into a working oscilloscope. It’s a small USB device with about a two square inch PCB footprint that includes some other features as well like a signal generator and logic analyzer. It’s based on an ATxmega which is your standard Arduino-style AVR microcontroller but geared for low power usage. It looks as though it is pretty simple to use as well, and the only requirements are that you can install the software needed for the device on whatever computing platform you decide to use.

While the Labrador is available for sale at their website, it is definitely a bonus when companies offer products like this but also release the hardware and software as open source. That’s certainly a good way to get our attention, at least. You can build your own if you’d like, but if you’d rather save the time you have pre-built options. And it doesn’t hurt that most of the reviews of this product seem to be very favorable (although we haven’t tried one out ourselves). If you’d prefer an option without a company backing it, though, we have you covered there too.

GlScopeClient: A Permissively-Licensed Remote Oscilloscope Utility

May 30, 2019 by Ted Yapo 26 Comments

One of the most convenient things about modern digital oscilloscopes is that you can access the recorded data on a computer for later analysis, advanced protocol debugging, or simply the convenience of remote capture. The problem is that the software isn’t always ideal. Vendor-supplied utilities are typically closed-source and they try to nickel-and-dime you for every a-la-carte protocol and/or feature. The open-source options come with their own issues, from performance-limiting designs, to incomplete features, to license constraints. Faced with these issues, [Andrew Zonenberg] decided to take matters into his own hands and create glscopeclient, a permissively-licensed open-source remote oscilloscope utility.

The eventual goal is to allow you to do remotely anything you would normally do using the scope’s front panel, plus capture and analyze data on the computer side. The code uses a modular architecture that allows for various backends to talk to different scopes. At the moment, the only backend fully implemented is for LeCroy scopes, although this is enough to demonstrate the power of the idea. The obvious “gl” in the name gives away the secret — the code uses OpenGL for rendering, which allows for some very fancy graphics at high frame rates.

Behind the slick look, however, are some serious debugging tools. Protocol analyzers include USB, UART, JTAG, eye pattern analysis, plus FFT-based spectra with waterfall displays. The code is in GitHub, and most of the announcements and discussion seem to happen on [Andrew]’s twitter account, which you can follow @azonenberg. It’s a work-in-progress, but a serious one, and something we’re going to keep our eyes on.

You can check out a video of the program after the break.

Now, if you want to literally talk to your oscilloscope, we covered that, too.

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Repairing And Upgrading A HP 16533A Scope Card

May 10, 2019 by Lewin Day 17 Comments

In the world of oscilloscopes, as in the rest of the test equipment world, there’s always some trickery afoot. Companies will often offer different models to the market at different price points, in an effort to gain the widest possible customer base while also making the most profit. Cheaper, less capable models are often largely identical to more expensive hardware, save for some software or a couple jumpers that disable functionality. [Alexandre] found just this when working to repair his HP 16533A scope card.

Work began when [Alexandre] received his HP 16533A in the mail after a long wait, only to find the trigger functionality was inoperable. This is crucial on a digital scope, so this simply wouldn’t do. After some research online, a post was found discussing which signals to probe to troubleshoot the issue. It noted that corrosion is a common problem on these units, and that occasionally, a certain resistor goes open circuit and causes problems. Initial measurement showed there was still resistance there, but reading closer, [Alexandre] noted this fateful line:

You might not be able to measure it accurately in circuit.

Removing the 100K resistor from the board, the part was indeed open circuit. After replacement with a new component, the trigger circuit was again fully operational. With the scope still open, it was then a simple job to execute a further resistor swap which gives the 16533A the functionality and range of the higher-spec 16534A model.

It’s very common for oscilloscopes and other test hardware to be configured this way from the factory. Rigol scopes are particularly popular with hackers for this very reason.

[Thanks to jafinch78 for the tip!]

Power Measurement Oscilloscope Style

April 24, 2019 by Al Williams 7 Comments

If you want to measure voltage you reach for a voltmeter. Current? An ammeter. Resistance? An ohmmeter. But what about measuring AC power? A watt meter? Usually. But if you know what to do, you could also reach for your oscilloscope. If you don’t know what to do, [Jim Pytel] has the video answers for you. Truth is, an oscilloscope can measure almost anything if you know how. [Jim] shows how to measure the voltage and current in a circuit and then it is simply a matter of doing a little math, something modern scopes can do very easily.

We like that [Jim] shows a circuit and how the math works before he verifies the math with the scope. Of course, theory doesn’t always match practice. The method uses a small current-sensing resistor that throws readings off a bit. The scope and signal generator are not perfect, either. However, the results match up pretty nicely with the computed results.

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