Review: Agilent U8002A PSU

There’s a lot of debate out there over the merits of asking someone what they want for Christmas.  Does it defeat the purpose of buying thoughtful gifts which show how well you know someone?  Or does it accomplish the real goal of giving presents which are truly useful and desirable?  Well, I personally don’t have a problem with being asked what I’d like for a present.  Particularly when I can request, and receive, a sweet power supply like the Agilent U8002A:

Agilent U8002A PSU Yes, Santa my parents were very kind to me this Christmas.  Finally, more than 15 months after considering a handful of different supplies, I have one to call my own.  And interestingly, it wasn’t one of the supplies I discussed in my original list.  But I think it still meets my original set of requirements fairly well:

  • Output voltage: 0-30V, 10mV resolution
  • Output current: 0-5A, 10mA resolution
  • Output voltage ripple: 0.01% + 2mV (5mV @ 30V)
  • Output current ripple: 0.02% + 2mA (3mA @ 5A)
  • Cost: $396

So far I’m very pleased with this supply.  My multimeter indicates that its voltage and current readings are spot-on.  This is no surprise though, considering that it came with a calibration certificate from Agilent.  I also attempted to measure its output voltage ripple using my Red2 IOBoard, but quickly discovered that I didn’t have the necessary ADC resolution (in other words, the output was so clean I couldn’t measure any ripple or noise).

The interface on the U8002A is quite nice.  Simple yet powerful.  I particularly like the fact that I can adjust its voltage and current limits before enabling the output.  This is one feature that would have been missing in most of the cheaper power supplies I looked at.

Agilent U8002A - Display Limits while Off

Just out of curiosity, I ran one more test while I had my IOBoard out and connected. I connected up a 20Ω resistive load and enabled the output while logging data:

Agilent U8002A Power-on Response

That little cut in the voltage just before the output reaches steady-state is a little odd.  Not that I’ve looked at a lot of PSU transient responses though.  It just seems like the control is doing something strange there.  Perhaps some sort of filter capacitor gets switched in and we hit a brief current limit?  Who knows…  It’s not a problem though.  I’d be more concerned if the voltage had overshot the limit, but that’s clearly not the case.

Overall, if you’re looking for a PSU with specs like this one, I’d highly recommend the U8002A.  It’s made by Agilent, so you know it’ll be a quality piece.  And yet it’s reasonably priced (unlike most of their hardware).  Let me know if you have any questions about it.

Ozone and Earthquakes?

Tangshan Earthquake (1976)The words “earthquake” and “ozone” are two terms you don’t often find used in the same sentence.  Like “congress” and “effective”, or “health food” and “delicious.”  And yet, MSNBC recently published an interesting news item whose title did just that: “Is ozone gas an earthquake precursor?

As it turns out, when rocks such as basalt and granite are crushed, they produce substantial quantities of O3 – ozone gas.  According to researchers at the University of Virginia, the amount of ozone released varied between 100ppb and 10ppm.  To put that into perspective, the low end of this range is comparable to a very smoggy day in Los Angeles.  The high end is one hundred times worse.

So I guess now we’ve got yet another reason to hate earthquakes: they split houses, swallow cars, and pollute the air.  Although, perhaps if a quake destroyed enough cars this would offset the amount of ozone released.  But I digress.  The real question here is, “Can elevated ozone concentrations predict earthquakes?”  Well according to researcher Catherine Dukes, no, not really: “It’s just a way to warn that the Earth is moving and something — an earthquake, or a landslide or something else — might follow.”

I suspect that any rock crushing action which produces ozone is also detectable via seismograph (although I’m just guessing).  So perhaps this discovery isn’t so useful.

But crushed rocks producing ozone?  This is still a rather strange phenomenon.  Scientists are not yet certain of the precise mechanism at work here, but suspect that differences in electric charge between rock surfaces are the most likely cause.  As you may know, lightning strikes are another natural means of ozone formation, particularly in the upper atmosphere, where ozone is more beneficial.  While the strike itself does not directly form ozone, it breaks apart O2 into atomic oxygen, which may then recombine as O3 (see this PDF for details).  Lightning also yields nitrogen oxides (also a popular automotive pollutant) which, in the presence of sunlight, react with other chemicals to form ozone.  So the theory here is that differences in electric charge between the crushed rocks are producing small electrostatic arcs (miniature lightning strikes) which result in ozone gas.

Well, perhaps we should just chalk this up as another oddity of the universe – like X-ray-producing tape, or radioactive bananas…  Still, it would interesting to know if there are preliminary tremors which aren’t detectable by seismographs but might be picked up by ozone detectors.  Such predictions probably wouldn’t be too accurate though.

Happy New Year

Greetings People of the Internet!  First off, Happy New Year!  The last twelve months have proven quite interesting, yes?  Whether good or bad, I think the term “interesting” is fairly safe here.  I can’t say my 2011 has been all that great, but it’s certainly been interesting.  I do hope, however, that you’ve had a good year.  🙂

One other quick note; in case you’re wondering what happened to Grieg, he died of heart failure in 1907.  And in case you’re wondering what happened to (my former domain name), I finally bit the bullet and purchased a real address for this trite little blog:  If you subscribe, you may want to update your links (although I intend to leave alive and forwarding for as long as the internet allows).  Please let me know if you have any issues.

As usual, keep the comments and questions coming.  Best wishes for a successful 2012!

New Toys: Bus Pirate and Digipots

That’s right, I’m now the proud new owner of a Dangerous Prototypes’ Bus Pirate.  I’ve been looking at these things for awhile, and finally decided that I should stop being such a cheapskate and just get one.  Yea, I know I can always rig up one of my AVRs to do serial communications, but this is just so much more convenient.  And at $30 (I got mine from SparkFun), it’s a pretty sweet deal.

Bus Pirate Closeup

So what did I get for my three Hamiltons?  Well, check this out (courtesy SFE):

  • Supported protocols:
    • 1-Wire
    • I2C
    • SPI
    • JTAG
    • Asynchronous serial
    • MIDI
    • PC keyboard
    • HD44780 LCD
    • 2- and 3-wire libraries with bitwise pin control
    • Scriptable binary bitbang, 1-Wire, I2C, SPI, and UART modes
  • 0-5.5volt tolerant pins
  • 0-6volt measurement probe
  • 1Hz – 40MHz frequency measurement
  • 1kHz – 4MHz pulse-width modulator, frequency generator
  • On-board multi-voltage pull-up resistors
  • On-board 3.3volt and 5volt power supplies with software reset
  • Macros for common operations
  • Bus traffic sniffers (SPI, I2C)
  • A bootloader for easy firmware updates
  • Transparent USB->serial mode
  • 10Hz – 1MHz low-speed logic analyzer
  • Scriptable from Perl, Python, etc. (aka everything)
  • Translations (currently Spanish and Italian)
  • Enumerates as a virtual COM port over USB
  • Can operate as AVR STK v2 clone programmer
  • Access to PIC24FJ64 ICSP programming port

Needless to say, the Bus Pirate’s capabilities are extensive.  And open source.

Thus far I’ve tested out its UART and SPI modes, and have been sufficiently impressed.  Which leads me to my next new toy, an SPI digital potentiometer, the MCP42010:

MCP42010 Digital Potentiometer

This particular part comes in a 14-DIP package, contains two 10k potentiometers with 8-bit resolution, and can be had for just $2.40 from Digi-Key.  I’m thinking of using it in an audio compressor / volume control prototype, but it may come in handy elsewhere.

Controlling this digipot is just ridiculously easy when using the Bus Pirate.  Once connected and in SPI mode, I simply issue the command “[0b11011111, x]” (without the quotes), where x is a value from 0-255 representing the potentiometers’ wiper positions.  The two least significant bits (11 above) of the first byte tell the chip which of its potentiometers to adjust.  You can set one at a time, or both simultaneously.  Bits 4 and 5 of the first byte (01 above) allow you to either write data to the wiper registers or put the digipot into a high-impedance shutdown mode (which could be great for reducing power consumption).  The same effect can be achieved by pulling pin 12 low.  Want to reset the potentiometer to its 50% position (this also happens automatically on power-up)?  Pin 11 will do just that when pulled low.  For all the gory details, take a look at this datasheet.

Bus Pirate and Digipot Test Setup

This little chip is pretty impressive.  It’s also available in 50k and 100k versions.  The only thing it really can’t do is handle much current (wiper current should be kept under ±1mA).  But just toss in some buffer op-amps and you’ll be all set.  That’s my plan anyways.

LabVIEW: The Simple Talking Voltmeter

A couple of weeks ago I spent some time examining a fairly complex circuit board from my old, but still functional, clock radio/CD player.  I was using the probe of my handheld multimeter to measure voltages at various IC pins and circuit traces.  At one point during the process I thought, “Gee, wouldn’t it be nice if I had someone here to read the voltmeter to me as I test various points?  That way I could focus on my probe and not accidentally short neighboring pins.”  But then I realized that I did have someone to do just that: Microsoft Sam.  I present to you the NI LabVIEW talking voltmeter:

For those of you without LabVIEW, here are a few screenshots of the subVIs shown in the video above.  Don’t forget that you can always download a free, unrestricted 30-day trial of LabVIEW from the NI website (seriously, it’s awesome, you should try it).

First, the initialization VI, which opens the Microsoft ISpeechVoice reference:

Initializing the Speed Interface

Next, the blocks responsible for detecting new steady-state voltages:

Detecting New Steady-State Voltages

Finally, the code which converts numbers into strings and sends them to Sam:

Convert and Speak the Values

Many thanks to Grant Heimbach, whose sample speech VI saved me a lot of development time (his original code is available on the NI Developer Community).

Click here to download a simple example VI which utilizes the code shown above.

The full, unmodified IOBoard Voltmeter program, as well as all of its supporting components, can be located at the bottom of the Mobile Studio Downloads page.

Got questions or comments?  As always, feel free to leave them below!