# Ocean Controls

Member Since: March 21, 2007

Country: Australia

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### Websites

www.oceancontrols.com.au

• "-200°C to +700°C Temperature Reading with ±2°C Accuracy" might be a little misleading. The chip is ±2°C accurate to it's internal linear model of the thermocouple temperature as a function of thermocouple voltage. The voltage produced by a thermocouple is not a linear function of the temperature (though a linear model is okay for many uses).

For example, at 700º, a K-type thermocouple generates 29.129 mV. [1] This chip calculates the temperature using T = V / (41.276 * 10 ^ -6). So for 700º, it'd report 705.713 º ± 2 º.

At -200 º the problem is much worse. -200 º on a K type thermocouple is -5.891 mV. This chip would report -142.72 º ± 2 º.

Also, the uncertainty of the cold junction measurement needs to be added to the uncertainty of the thermocouple measurement if you're talking about the accuracy of a typical temperature measurement using this chip. Even ignoring the problems due to the linear model, the uncertainty of a temperature measurement should be considered to be ±4 º.

You could take the value reported by this chip and in your code reverse the linearisation and CJC compensation to get the thermocouple voltage. You could store the thermocouple voltage table in your micro (or some clever piecewise linearisation of it) and use that to get a more accurate temperature measurement, but it seems like a lot of work compared to using your own ADC and CJC sensor.

[1] http://www.ni.com/white-paper/4231/en/#toc2

• That's about 150 mm for those of us who live in one of the ~98.5% of the world's countries that use the metric system.

• The MAX481 datasheet says maximum data rate is 2.5MBPS not 10MBPS. Both Donn and Alberto are correct. I cannot see how you can control the Driver enable and receiver enable using the TXD signal. When a byte is transmitted some bits will be zero and the Driver enable will be off and the driver output will be in tristate.

To get 10MBPS over 4000feet using RS485 is fanciful. There are no termination resistors to handle ringing and reflections. I have experienced situations in industry where I needed a RS482 repeater to transfer data over 1Km at 9600BPS.

• I did the same for the Galaxy Nexus but a couple of seconds on the belt sander was all it took to convert this to a microB compatible plug.

• Check out this tutorial on using this with a WiFi shield and a couple of other SFE bits to get internet controlled relays.

• Should probably point out that if they have condensation on them they won't work (normally output 0%RH)and may also need to go through the baking and re-hydrating process if they don't recover.

1. There is no inhibit input on this model
2. Thought you can teach it 2 different coins, the output signals seem to be the same for each coin, even though the device recognises the different coins by flashing the LED associated with that coin.
• Will you consider stocking some of the upgrades/spares? I have an old one and the precision egg coupler and diamond engraving tool look useful. I've upgraded mine to use hot wax, video here.

• This kit requires raisin-core solder, is SparkFun going to stock raisin-core solder or perhaps some currant or sultana based alternative or can I use regular rosin-core solder?

• Underneath the TQFP package footprint is the QFN package footprint (no legs) which means that if the supply of one type of chip dries up production can continue with the other type without much hassle.

No public wish lists :(

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