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  • EEVblog #9 – ThermoChron iButton and Microchip PICkit2

    Posted on May 17th, 2009 EEVblog 10 comments

    TI buys Luminary Micro, Maxim/Dallas ThermoChron iButton, Microchip PICkit2


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    • Eldon R. Brown

      David,

      I love your “Video Blog”, I started with with your first and now always looking forward to next.

      I like people that “tell it like it is”, or at least have an opinion (good or bad) with some logic to back it up.

      Good luck and Thanks,
      Eldon

    • http://doitle.markdelano.com Mike Firman

      Howdy David,

      Just found your blog last night and stayed up late watching all the old episodes!

      I was wondering though after seeing you talk about the burden voltage problems in multimeters why they use a shunt resistor at all. I understand that it is cheap and simple for something like the 20$ handheld chinese multimeter but what about a really expensive Fluke? Why don’t they use a hall-effect current sensor to measure current instead of the shunt resistor.

      I used one recently for a Powerfactor detection project and it was very easy to setup and use. This would eliminate any burden voltage problems and give you a nice accurate reading of current. Perhaps there is a fairly obvious reason I am not seeing but it makes sense to me to use a hall sensor in this instance.

      Anyhow keep up the awesome podcast, I’ll surely be watching!

      • http://www.alternatezone.com/eevblog admin

        Shunt resistors are cheaper and have greater precision and linearity etc than hall effect sensors. Makes sense to use them in a general purpose multimeter. Burden voltage can be tolerated for the majority of applications.

    • ewertz

      All shunts aren’t created equal. Sure, the cheaper the shunt, the greater the burden voltage. But they’re almost always cheaper and more accurate than both CTs and Hall-effect sensors, I believe.

      Shunts do become less accurate once they start to self-heat, but for lower-current applications, they almost can’t be beat. CTs and HES’s tend to have non-linear responses over wide ranges and also will vary with temperature. HES’s can also have offset drift problems as well as non-linear phase shift problems, and CTs can have saturation problems. By the time you compensate for these problems, you’ve increased your costs significantly.

      However, if you need a non-contact solution, the CTs and HES’s are clearly the way to go. You often don’t want to (or can’t) be sticking a shunt into a live DUT, but if you’re building a sensor into a device to stay there (like a power panel), an appropriate shunt is often going to be your first choice.

      I’d say the same about your metering project. If you aren’t building the meter/sensor into the project to stay there, then you don’t have much of a choice other than to use a CT or Hall-effect sensor. But accuracy will suffer unless you’re willing to do all of the compensation required, *especially* the phase-shift issues for PF measurement.

      Most of the metering chip vendors have app notes that cover most of these issues. ADI, Microchip, Atmel, and Teridian come to mind.
      As usual, it all depends on what your accuracy, cost, and use constraints are.

      -e

    • http://hackedgadgets.com Alan Parekh

      Great videos. Thanks for taking the time to make them. Love the accent and terminology, Ducks Guts got me laughing in this episode!

      Keep up the great work.

    • Zach

      Can you recharge the Maxim/Dallas ThermoChron iButton? Does the uploader recharge it?

      • http://www.alternatezone.com/eevblog admin

        No, you can’t recharge it. Like I said, it’s a lithium cell with a 10 year battery life from the factory.

    • http://www.danielbjohnson.net Daniel

      I golf alot, and my favored driving range, recently changed their system from card readers to apparently these 1-wire iButton readers. And now have an iButton that keeps track of my credit. Thanks to your video, I immediately knew what it was. They have more security applications, and other applications besides temperature sensing also. I like the idea and the interface. I will definitely try to implement one of these in the future if the need arises.

    • Steve

      I agree, the PICKit 2 is awesome. Had mine for about 3 years. Ease of programming PICs is what’s kept me with Microchip for so long. I keep hearing great things about AVRs but I haven’t heard of any equivalent in the Atmel world.

    • http://www.nationalits.com.au/ nec servers

      Quite insightful publish. Never believed that it was this simple after all. I had spent a excellent deal of my time looking for someone to explain this topic clearly and you’re the only one that ever did that. Kudos to you! Keep it up