Reading resistance thermometers (PT100, PT1000)

Hi,
How to reading resistance thermometers (PT100, PT1000) with a Fez Domino or Cobra? Are there any converters (I2C?)?
I need many of them on one controller, up to 16.
How to archive that with moderate costs?

Have they analogue outputs?

I cant find a PDF on them.

I would personally use two CMOS 4051 8:1 analogue switches,but that’s only because I carry them in stock.

Cheers Ian

PT100/1000 are PTC resistors, they have no analog output, they are passive.
So I need to measure the precise resistance which I have to scale to the temprature

I have to use such PTC’s for temperature measuring, they are a industry standard. If a sensor is broken in 20years, it will be still available, and everyone could replace it easily.

http://en.wikipedia.org/wiki/Resistance_thermometer

I’m not an electrician engineer so I need some assistance to design such a circuit. Maybe there is something ready to use. I want to avoid redundant components because of the up to 16 thermometers.

I found this very interesting:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1248751435

What accuracy do you require?

Also, if you have a choice, go for the PT1000. They hace 1k ohm resistance at 0C.

The simplest config will be to connect a PT1000 in series with a 1k resitor between 0V and 3.3V. and connect the center of the two to an analog pin on the board. The up side is that it is very cheap. The down side is that you get less then 1 degree resolution and you can only connect 6 sensors as the boards only have 6 analog ports.

You can use a MUX as IanR said, that will increase your sensors but resolution stays low. That will require more electronics…

I use a similar device that uses a 160 ohm pressure switch.

I use a constant current to read the maximum possible and to keep it linear.

There are a few components needed but I only read 5 pressure sensors.

Cheers Ian

Accuracy should be about 0.1
I found some PT1000 to I2C, SPI, UART, converters. But only one sensor can be connected and they cost about 100€. :frowning:

I’m dusting off a couple of old FEZ projects and I am looking for some sample code for the “zx-thermometer” GHI has sold in the past. Is there an archive around which contains the sample code which use to accompany the peripheral devices sold on the GHI site?

@ Nicholas - Is that what you are looking for?

https://www.ghielectronics.com/downloads/FEZ/Component/FEZ_Components_Thermometer.cs

Also on codeshare:

https://www.ghielectronics.com/community/codeshare/entry/22

Yes, that is what I was looking for.

Thank you.

Funny about the “old thread”, I made good progress a few years back on FEZ hardware. Now with IoT being such a popular topic, I have a need to re-engage.

@ Nicholas - Welcome back!

Can you share your code?

not sure why you need, since the references a few posts back are the ones that provide the info?

I have a trouble when i reading the outvoltage, the value change
continuously, Vcc 3.3

have you tried just with a voltage divider with regular resistors, and see if the same variation happens ?

Anyway, sounds to me like you should start your own thread and give us all the background. The code attached to those two links earlier should give you all the details you need to make sure your approach is OK, and then the rest becomes a voltage problem (wiring related)