Keithley DMM7510 monitors Charger Doctor Output

The Charger Doctor is a sub $2 device that displays voltage and current levels while charging a USB device.  There have been several teardown write ups on the Charger Doctor.  It's useful, but does have some limitations.  For example, it doesn't charge iOS devices and it seems to effect the reliability of the WiFi connection on our Raspberry PIs.  This made us want to take a closer look at what the output was doing.

Here we use a Keithley DMM7510 to monitor the Charger Doctor output.  The DMM7510 is a precision instrument with 7.5 digits of resolution and 14 PPM accuracy.  It has a touch screen interface with graphical output, advanced triggering options, cursors, and a whole lot more.  Plus, it is fast (very very fast); capable of sampling at 1M/s.  To sum it up, it's pretty darn cool!
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In the video the DMM7510 shows a decrease in voltage when the Charger Doctor displays current.  Also, some instability when displaying voltage.  But remember, the Keithley DMM7510 is a very sensitive instrument.  The change in voltage looks big on the screen, but it is really very small.
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The overall voltage swing is only 7.536mV or 0.00753 Volts.  That's not a lot.
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And taking a closer look at that instability when the Charger Doctor displays voltage we see that it is only 1.256mv peak to peak; that's just 0.001256 Volts.  Really, that seems exceptional for a sub $2USD device.
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There is a lot of discussion on the web as to why iOS devices don't charge via the Charger Doctor.  With the stability shown, I'm not sure why the Charger Doctor effects the WiFi reliability of the Raspberry PI, but I can say it does.  We set the Keithley DMM7510 to camp on the Charger Doctor output signal and trigger on a larger glitch or voltage spike to give us a clue.  After about 15 minutes the Charger Doctor remained stable within the trigger limits and we moved on with our life.  We do have to take into account that the Charger Doctor was effectively unloaded while making these measurements and that could make a big difference.
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Thanks for stopping by.
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Tektronix MDO3000 as a MP3 Player

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A friend of mine got a Pono music player this Christmas.  The claimed advantage of the Pono player vs other music players is better sound fidelity.

So what does the Pono player do different?  Normal CD music is sampled at 44,100 times per second (44.1Ks/S) and 16-bit resolution.  The Pono is capable of playing music with an increased sample rate of 192,000 times a second (192Ks/S) and 24-bit resolution. A quick web search yields page after page of audiophiles debating these fidelity claims and we will leave that discussion to the experts.
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Since Pono advocates see benefits in increasing sample rate from 44,100 times per second to 192,000 times a second, then just think about how awesome really turning up the sample rate would be!!!  But how?  Enter the Tektronix MDO3000 which can sample at an amazing 2,500,000,000 (2.5Gs/S) times per second and that's a lot!
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The Tektronix MDO3000 is a benchtop instrument that has some truly amazing capabilities that push it way beyond being just an oscilloscope.  One of these features is the Arbitrary Function Generator (AFG) that can capture signals from any of the analog channels and play them back on command.
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In the video below, we set the Tektronix MDO3000 to sample at a lazy 1,000,000 times per sec (1Ms/S).  Then we use a PC to play a MP3 music file for capture into the instrument's waveform memory via analog channel 1.

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Next, with a few button clicks the music waveform we just captured is loaded into the instrument's AFG to make it ready for playback.  Simple.

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The Tektronix MDO3000 AFG output is BNC connector on the back of the instrument.  We connect to the AFG and plug into a speaker.  The result: The most impractical (and expensive) MP3 player available, but with an impressive sample rate many, many times higher than the Pono player.

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This whole experiment means nothing, of course.  We did it simply because "we could".  If you do decide to go with a Pono (or a Tektronix MDO3000) as a music player remember that much of the sound quality is determined at the time of the original recording and not just at playback.  Also your headphones, speakers, listening room, ears, etc...

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DS Nano v2 Oscilloscope Performance

The DS Nano v2 is a very low cost 1-channel oscilloscope that, for the ~$80US price, has served me pretty well for my hobby electronics.  The scope came with a nice soft case and two sets of "probes".  It has other features as well.

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This page is not intended to put down the little DS Nano v2.  The scope behaves as advertised.  For example, I had a project that required a piezo sensor input.  Things were not working according to plan and the DS Nano v2 was able to capture the low frequency signal from the piezo and suggest that a diode was needed to tame the signal for use as a microcontroller input.

Here is another example of the DS Nano v2 doing a great job showing variable pulse width from a simple PICAXE18 program:

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That said, the DS Nano v2 does have its limits and I always wanted to compare it to a "real" oscilloscope.  I was able to get my hands on a Tektronix MSO2042 Oscilloscope and Tektronix AFG3252 Signal Generator.  The AFG3252 can produce waveforms up to 240MHz extremely accurately.  Well in the range for our purposes as an input source.

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The table below compares some key specs of the DS Nano v2 and the MSO2042:

Again, for our test purposes the Tektronix MSO2042 Oscilloscope is way more than adequate to test the DS Nano v2. 

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So what about the results?  Below are some screen shots of signals with increasing frequency.  The DS Nano v2 is the smaller screen in the foreground.  The Tektronix MSO2024 is the larger screen in the background.  Both  oscilloscopes are connected to the same signal source in parallel with no concern for impedance matching (note the ringing).   You can immediately see that DS Nano fails miserable at detecting the  high frequency ringing.  But let's be fair; the DS Nano spec is 200KHz for analog bandwidth, so this result is not a surprise.

One important thing to look at in the pics below are the voltage level cursor lines on the DS Nano v2.  You will notice that there is really no attenuation in the signal the DS Nano v2 displays as we test to its 200KHz bandwidth; that's good.  However, the limit of the 1MS/s sample rate does start to show.  The 100KHz signal pic really shows how the DS Nano v2 sample rate effects the displayed output.

All that said, it you are looking for a <<$100US scope that will fit in your pocket, the DS Nano v2 is a handy choice.  If you use it within it's specs it is a great value!  If you need more call Tektronix!

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