Analyzing Hobby Motors with an Oscilloscope

We always like finding new excuses reasons to use our test equipment, so we couldn’t help but be intrigued by this tip from [Joe Mosfet]. He uses the ever-popular Rigol DS1054Z to demonstrate the differences between a handful of brushless motors when rotated by his handheld drill at a constant RPM. Not only is he able to identify a blown motor, but it allows him to visualize their specifications which can otherwise seem a bit mystifying.

One wire from each motor is used as the ground, and channels one and two are connected to the remaining wires. Despite the DS1054Z having four channels, [Joe] is actually only using two of them here. The third channel being displayed is a virtual channel created by a math function on the scope.

After wiring them up, each motor got put into the chuck of his drill and spun up to 1430 RPM. The resulting waveforms were captured, and [Joe] walks us through each one explaining what we’re seeing on the scope.

The bad motor is easy to identify: the phases are out of alignment and in general the output looks erratic. Between the good motors, the higher the Kv rating of the motor, the lower voltage is seen on the scope. That’s because Kv in the context of brushless motors is a measurement of how fast the motor will spin for each volt. The inverse is also true, and [Joe] explains that if he could spin his 2450Kv motor at exactly 2450 RPM, we should see one volt output.

Beyond demonstrating the practical side of Kv ratings, [Joe] also theorizes that the shape of the wave might offer a glimpse into the quality of the motor’s construction. He notes his higher end motors generate a nice clean sine wave, while his cheaper ones show distortion at the peaks. An interesting note, though he does stress he can’t confirm there’s a real-world performance impact.

Last year we featured a similar method for identifying bad brushless motors using a drill press and an oscilloscope, but we liked that [Joe] went through the trouble of testing multiple motors and explaining the differences in their output.

[via /r/multicopter]

Homebrew Analog Scope Project Log

[GK] had some old CRTs lying around, so naturally he decided to build an old school analog scope with one of them. Lucky for us, he’s been documenting his progress. Since it was a big project to tackle, he started out with Spice modeling to work out all the right values.

Prototyping the power supply took some custom transformer winding, but when done, the power supply did the job. Although he’s still wiring up the Z (intensity) axis, the scope is already capable of displaying signals and even text characters using a character generator he built earlier (see video below).

[GK] spends most of the time so far talking about the high voltage power supply design. For the particular tubes he had on hand he needed +200V, -400V, -550V, and 6.3VAC for the CRT heater. This is certainly not the typical Arduino-based digital scope that everyone builds at least once.

We love analog scopes for art projects, logic analyzer conversions, and gaming. Of course, if you don’t have an old CRT in your parts bin, you might consider trying a laser.

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Fast ADC Uses Old School Scope Hack for 48 MSPS

[Carlos] needed an ADC with a 50 nanosecond sample period for his laser lab, that’s 20Msps! (20 million samples a second). While in recent years, commodity ADCs reaching into the low GSPS have become available, integrated acquisition systems are still somewhat expensive. So [Carlos] decided to do what every good hacker does, and built his own solution. His project post pretty much just links to a whitepaper he wrote (PDF) so we’ll try and boil it down for you:

In order to simplify development [Carlos] borrowed a technique commonly used in the first era of digital oscilloscopes, Equivalent Sampling Time.


The figure to the right is from the TDS460 manual. While it may seem counter intuitive to those only familiar with modern scopes, the TDS460 achieved a 400MHz bandwidth using a 100MSPS ADC. In order to achieve this the scope acquires a single trace in multiple cycles, each time offsetting the acquisitions as shown and combining the result.

In this way, early digital scope developers could sidestep the limitations of the available ADCs to achieve a higher effective bandwidth. However there is of course one catch: the technique only works for periodic signals.

This was fine for [Carlos] who implemented a technique on a Cypress PSoC 4, which provides analog FPGA-like functionality. By offsetting the ADC trigger he has able to achieve an EST of 48MHz using a ADC sampling at 1MHz. If you want a little help getting into PSOC 4 yourself, check out the guide that [Bil Herd] made.

Neat hack [Carlos] and we hope to hear more about your laser lab in the future.

The One Million Dollar Scope Teardown

The Labmaster 10-100zi Oscilloscope is one of the fastest scopes in the world, coming in at a blistering speed of 100GHz with up to 240 Giga samples per second in real time. The scope is made by Teledyne LeCroy, and uses a frequency interleaving technology perfected by LeCroy, which allows it to provide a single 100GHz channel, or two 33GHz channels and a single 65GHz channel. The price tag? One million dollars.

[Shahriar] takes us inside the Teledyne Lecroy factory in Chestnut Ridge, NY where these scope are manufactured, and gives us the grand tour. First, an engineer describes the interleaving frequency technique that allows the lightning fast sample rates. Then they actually tear the million dollar scope down for our viewing pleasure. And if you still want more, they put it back together and run some tests to push the scope to its far reaching limits. Lastly, [Shahriar] takes us on a tour of the plant where the scopes are built.

It’s a lengthy video, so grab your favorite beverage and tuck in! It’s shocking how fast technology progresses. Just about 18 months ago [Shahriar] took us through the then reigning champion of scopes the Agilent DSA-X 96204Q which capturered 160GS/s at 62GHz.

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Vector Display Output on an Oscilliscope


What can we say, we’re a sucker for projects featuring our logo. That being said, this one is seriously awesome. [CNLohr] has figured out how to create a vector display output on an oscilloscope… from a VGA port.

He was inspired by a game called Trace Vector, which is done in the same style as some of the old classics like Asteroids. This got [Charles] thinking, and he decided to see what it would take to make his own vector capable display. An oscilloscope is perfect for this, as it already works by controlling the position of the beam (like a vector), as opposed to standard LCDs and CRTs that use rasterizing (horizontal scanning). This means to get the oscilloscope to display a graphic, all you need to do is to vary the voltages going into the X and Y channels — well, at a high speed!

But where are you going to find such a high speed digital to analog converter? Oh yeah, your computer’s VGA port! For a few dollars [Charles] threw together a VGA adapter with a few resistors using just the red and blue outputs (source code). A bit of programming later, and he’s created his own vector display!

Stick around to see our lovely skull and cross-wrenches rotate on his oscilloscope! Oh, and for a more in depth explanation and more impressive vector video demonstration.

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A keygen for the Rigol 2000-series scopes

A few weeks ago it came to our attention that Rigol’s DS2000-series oscilloscopes were easily unlocked with a few USB commands. We had expected a small microcontroller device would be developed to send these bits to a scope automatically, and we never imagined the final version of this tool hack would be so elegant. Now it’s possible to unlock a DS2072 o’scope using just a serial number and a great encryption hack.

The engineers over a Rigol (bless their hearts) used the same hardware for the $800, 70MHz DS2072 and the $1600, 200MHz DS2202. The only difference between the two are a few bits in the scope’s memory that are easily unlocked if you have the right key. A few folks over on the EEV Blog forum figured out the private key for the scope’s encryption and the user [cybernet] wrote a keygen.

The upgrade process is extremely simple: get the serial number of your DS2072, put it in the keygen, and enter the resulting key into the scope. Reboot, and you have a $1600 scope you bought for half price.

Unlocking a Rigol scope once again

Rigol scopes are finding their way onto the workbenches of makers the world over. There’s a reason for that – they’re so easily upgraded. With a simple software update, you can turn the 50 MHz Rigol o’scope into a model with 100 MHz of bandwidth. Design decisions in one model are sometimes carried over to different product lines, so eventually someone would figure out how to turn the 70 MHz DS2072 scope into the 200 MHz DS2202. A great mod that turns an $800 oscilloscope into one with the features of a $1600 scope.

There’s no internal modifications necessary for this mod; it works simply by sending a few engineering unlock codes to the scope over USB, a simple task that [Blair] implemented with a Raspberry Pi and a bit of Python code. The only fault of the hack is the scope resetting each time it’s powered off. This can, in fact, be accomplished with just about any microcontroller with a Python interpreter.

A fairly uninformative demo video is available below, or you could check out the EEVBlog thread where this mod was conceived here.

We here at Hackaday expect a small, cheap USB/microcontroller dongle thingy that automagically updates the DS2072 to show up in our inbox any day now. We thank whoever sends that in.

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