# temperature sensor for my soldering iron

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#### dodongkulas

##### New Member
hi guys!! I'm planning to build a controller for my soldering iron which is 30 watts using PIC microcontroller and I have a problem on what temperature sensor to use sense the temperature reaches 300+C.... Guys will you help me!!!!

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#### hyedenny

##### Guest
YIKES... Youd be better off using a variable current control, or PWM, and calibrate it with a thermometer. Where did you plan on putting this temperature sensor?!

#### justDIY

##### Active Member
you need a thermocouple junction ... like a K-Type or J-Type ... all it consists of is some wires (of known properties) soldered together and an amplifier to read out the voltage generated at the junction, and some filters to weed out noise.

you should be able to find a thermocouple "chip" that handles all that for you and outputs either serial or voltage. then you just need a way to work the junction itself into your iron, so it properly senses the tip temp.

sounds like an interesting project!

amplifier chip:
https://www.sparkfun.com/commerce/product_info.php?products_id=307

thermocouple probe:
https://www.sparkfun.com/commerce/product_info.php?products_id=251

I notice the probe is rated to 1372°C, but it's insulation is only rated to 260°C ... so you'll need to find someway to insulate it when it's near the heating element ... I don't know why glass braid insulation is only rated to 260°C - glass melts at a lot higher temp then that.

H

#### hyedenny

##### Guest
Thermocouple junctions are not "soldered," theyre resistance welded, or just twisted together...

You'll have to compensate for the cold junction also. Then you still have to figure out where to put the thing! You wont be able to solder with it since it will be in your way. One thermocouple will probably cost more than your lousy soldering iron anyway. And the AD595 cold junction compensation chip aint cheap either ($17-$25)!

Current control, or a new soldering pencil, is way more practical.

#### falmeshon

##### New Member
i'm no expert on this but would using a thermistor (temperature dependent resistor) work at such high temps?

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