Arduino - Simulate linear resistor...

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agorts
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Arduino - Simulate linear resistor...

Post by agorts » Sun Nov 14, 2010 1:11 pm

I want to simulate a linear resistor (temperature sensor)... I want to use instead of the sensor, something else (arduino?) and be able to set my own values...

How can I do this?

With Arduino?

paul
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Re: Arduino - Simulate linear resistor...

Post by paul » Mon Nov 15, 2010 3:37 pm

agorts,

I'm not quite sure what you are trying to do, so maybe try again, to tell me the big picture with more details.

Paul

agorts
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Joined: Sun Nov 14, 2010 12:48 pm

Re: Arduino - Simulate linear resistor...

Post by agorts » Tue Nov 16, 2010 1:09 am

I want to simulate a linear resistor (temperature sensor)... I want to use instead of the sensor, something else (arduino?) and be able to set my own values...

The device is: http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0433276940 and it has s sensor like this: http://www.seeedstudio.com/depot/temper ... 78.html?cP... Both of them are similar to a NTC 10K sensor...

With the digital potentiometer is it possible to set values in the range of 133.500KOhm-0,339968KOhm? As you can see in the second link...

paul
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Re: Arduino - Simulate linear resistor...

Post by paul » Tue Nov 16, 2010 8:55 am

OK - so I'm still not sure what you want to do. Hack the ebay temperature gauge or make one of your own? It's a fairly easy task to hook a thermistor up to an Arduino and make a lookup table to read the temperature.

Thermistors are not linear so a lookup table is probably a better idea than an algorithm, but there are curves that have been worked out.

Paul

agorts
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Joined: Sun Nov 14, 2010 12:48 pm

Re: Arduino - Simulate linear resistor...

Post by agorts » Tue Nov 16, 2010 10:39 am

I want to use the display in order to show different readings... So I want to cut the sensor and some-how connect something and be able (through Arduino) to change the resistor value (and so the displayed temperature) to what value I need....

paul
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Re: Arduino - Simulate linear resistor...

Post by paul » Tue Nov 16, 2010 11:27 am

This is not going to work "through the arduino" since the input is a resistor (hence current).

You can try different thermistors, and you will definitely change the reading, and you may be able to get one temperature close to what you want, but unless you wish to do a lot of experimenting, and playing with math, it's going to take a while to make the display work as you wish.

The Murata thermistor datasheet might be helpful - it contains curves for all their thermistors

Paul

agorts
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Joined: Sun Nov 14, 2010 12:48 pm

Re: Arduino - Simulate linear resistor...

Post by agorts » Tue Nov 16, 2010 4:25 pm

If there is something like a digital resistor with the ability to set the precise value, then I could control it through the arduino and set the desired value (resistance) and do the trick...

grgtrpp
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Joined: Wed Sep 30, 2009 9:43 pm

Re: Arduino - Simulate linear resistor...

Post by grgtrpp » Wed Nov 17, 2010 9:31 am

It sounds like you may want something like this: http://www.analog.com/en/digital-to-ana ... oduct.html
There is example code for Arduino at http://www.arduino.cc/en/Tutorial/SPIDigitalPot

paul
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Re: Arduino - Simulate linear resistor...

Post by paul » Wed Nov 17, 2010 12:01 pm

True - a digital pot could work - at a certain point though it's probably not worth the bother with the display - unless there's something in that display that is really attractive. How about a graphic display?

Paul

agorts
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Joined: Sun Nov 14, 2010 12:48 pm

Re: Arduino - Simulate linear resistor...

Post by agorts » Wed Nov 17, 2010 2:06 pm

Yes I know it does not mean any sense to try to use the display, but I want to try it...

What digital pot do you suggest me? The one in the example is 6 channel and I need only one...

I find a lot of sample staff and examples about DS1803 but I cannot find it to buy...

Any suggestions?

paul
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Re: Arduino - Simulate linear resistor...

Post by paul » Wed Nov 17, 2010 2:47 pm

Here's one place http://search.digikey.com/scripts/DkSea ... -010%2B-ND

it costs almost as much as your display though. Also I think Digikey charges a $5 fee until you get to $20. You could try Mouser.com

Paul

agorts
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Joined: Sun Nov 14, 2010 12:48 pm

Re: Arduino - Simulate linear resistor...

Post by agorts » Wed Nov 17, 2010 3:26 pm

Yes I know this is the only place I find it... all 3 types of them... mouser has only one of them....

Any other suggestions for digital pots?

What is better, SPI or I2C?

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