Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: clone on September 05, 2009, 05:09:00 PM
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I am making a digital thermometer using an arduino. I was gonna base my code off of this to make it http://www.arduino.cc/playground/ComponentLib/Thermistor2 (http://www.arduino.cc/playground/ComponentLib/Thermistor2)
it says to use a 10k thermistor and a 10k resistor. the electronics shop i went to didnt have 10k thermistors, so i got a 4k7, 30k, and 50k.
I want the thermometer to measure between 0-250 degrees F. Which one should i use, or does it even matter?
thnx.
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Well if it says 10k and has been proven by others go with 10k.
If you want thermisters have a look here
http://www.futurlec.com.au/test13.jsp?category=THERMISTORS&category_title=Thermistors&main_menu=OTHERS&sub_menu=THERMISTORS (http://www.futurlec.com.au/test13.jsp?category=THERMISTORS&category_title=Thermistors&main_menu=OTHERS&sub_menu=THERMISTORS)
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well i already have 3, so im gonna end up using one of them. plus i dont wanna purchase online because of the wait and shipping costs.
I guess i need to clarify what I want to know about thermistors. what determines a thermistors temperature range? what is the difference between a 1k thermistor and a 10k thermistor? Does the 10k have more precision or something? whats the difference between the various types of thermistors? I have one thats labeled 'bead' another thats labeled 'disk' and another that isnt labeled but looks weird.. i also saw some that look like a disc capacitor. attached are some pictures of the ones i have.
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Hi,
what is the difference between a 1k thermistor and a 10k thermistor?
The resistance obviously ;D
Does the 10k have more precision or something?
Nope.
whats the difference between the various types of thermistors? I have one thats labeled 'bead' another thats labeled 'disk' and another that isnt labeled but looks weird.. i also saw some that look like a disc capacitor.
Bead thermistors are shaped like, well, small beads and disks are... You guessed it - Disc shaped.
The smaller the physical size (mass), the faster it reacts and v.v.
Some are like the head of a pin for fast reaction (used on eg. the early variety of "instant" body thermometers). Some are integrated into various shapes of bolts and tubes etc. it's a matter of adapting shape to purpose.
attached are some pictures of the ones i have.
Ahemmm?
You can use either of the ones you have for the schematic you linked to, just use a resistor of the same value in the voltage divider.
The nominal value of a thermistor is the resistance at 25°C.
NTCs are non-linear devices.
You can either use a table to correct for this response, or, if less sensitivity is OK, it can be linearized to a reasonable degree by adding a parallel resistor (which must be matched to the specific NTC and the main temperature region it's supposed to act in).
It's a bad idea to go 0°F to 250°F, as the non-linearity will be vast over such a range.
In a body thermometer for instance, you only need a range of 35°C to 42°C, making the linearity error very small.
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i was planning on using the Steinhart-Hart Thermistor Equation to correct for non-linearity.
I actually only need a temperature range in the range of boiling water and alcohol for use in an automated still.
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Well, I decided to use the 30k ohm bead thermistor, because i found a data sheet pdf of a similar one on the internet. the data sheet showed the resistance for every 5 degrees celcius... so i ended up just using a lookup table type thing in my code instead of using the steinhart equation. Here is a video of the finished project!
Digital thermometer arduino project (http://www.youtube.com/watch?v=et_Wlga_eiM#)
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nice job clone, any chance of a shematic
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just drew this up super quick. i hooked up both 7 seg displays together.. pin for pin.. and the code in the arduino triggers the transistors to switch between the displays.. it does it super quick so u dont even notice that its only lighting up 1 display at a time. enjoy!
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LEDs did not burn out without resistors??
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nope.. didnt need any resistors. the leds aren't that bright as it is!
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Hi,
PIC outputs are internally limited to... around 25mA max. IIRC.