Friday, November 9, 2012

Back to the Original Purpose

Enough with the SDRs and Chumby's and other distractions. Well, mostly...

I've been a subscriber to EE Times for probably 20 years. It used to be a weekly paper like format, but is now a skinny magazine, but with amazing web bits to supplement it. A couple weeks ago, there was the an invitation to a webinar on RTD and Thermocouples put on by Maxim. The webinar happened on Wednesday, and I listened to it. Pretty good talk, the speaker couple have been more exciting, but was well prepared, and talked about some good products. He didn't convince me to switch to RTD's but I am now thinking of using an integrated SPI chip to do everything.

The webinar hammered into me the reason for the second temperature sensor at the cold junction. The reason is, that ends up being a second thermocouple, since the copper wires that we are connecting to are of different material than the wires in the thermocouple. If we don't know that temperature, then the actual temperature we want to measure will be off a bit. Having the second temperature sensor will add to the complexity, and cost of the circuit.

The one complex circuit presented used the MAX6126 for voltage reference, and DS600 for the cold junction temperature sensor and the MX7705 for A/D converter. There was some discussion about keeping a constant current source, and other details using these three chips to get a good measuring circuit.

Then he showed the MAX31855, wow, pretty simple. Connect the thermocouple on two pins, some power on a couple more pins, a crystal and capacitors on other pins, and then the SPI to the processor and you are done! About the simplest convertor I have seen for under $5! It does SPI, so I should be able to piggyback 8 or 12 or 16 depending on engine chosen. I won't have to use up the A/D convertors to get past a 6 cylinder engine. There is an SPI library for the Arduino and everything.

Now I am still dreaming, I need to actually build something. I need to order about 8 of them, 4 J type, and 4 K type. DigiKey has them for about $3.55 each, but only if you order 2500 at a time! Single quantities are over $7.50 each, and hard to come by. Maxim is generous, and offers them as free samples. I was able to get 2 of each that way. Well, I ordered them tonight. They are just up the street, well some part of the company is (right down Beltline on Midway in Addison, probably 5 miles west, yup google maps says 4.7 miles).

Another toy

This is sort of related, since it is Android. I got an Mk808 android device. I say device, because I am not sure how to categorize it. It plugs into a HDMI port on a TV or monitor and uses that for a display. Otherwise it mostly acts like a tablet processor. There are no g sensors or touch screens, but you can plug in mice (or bluetooth mice) and control the desktop that way. It can run crackle or netflix, and youtube so it is good for an entertainment device. It has a browser (two), and can read and write office like documents (or use google docs).

So what you say, I can get a tablet and do all that. How about replacing your PC with one of these? What would it hurt? You say you can't download photos to it, no you probably can't. You can't play games on it? Well, my kids are driving my wife nuts playing angry birds. You can download all kinds of games. It has the whole google play store on it. Games, apps and media are all available.

What if you wrote desktop type apps for it. Why not, you know, a 32 in 1080p monitor would be way cooler than two 20 inchers, there would be no line, and the mouse would smoothly slide between windows.

What does a desktop PC cost, $400, maybe $1000? Well this is under $100. Yes, that is right, 1.6GHz processor with 1GB memory isn't much, but it might be worth a try? EBay has 'em for about $50 if you want to experiment and don't want to blow too much. Get one of the fancy wireless keyboard mouse combos and you have a full multimedia center. Cut the cable and do some fun stuff.

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