Wednesday, December 20, 2017

MAX6675 termocouple reading

Got this little chip already assembled as a module and with a type K thermocouple included, idea is for some other project and/or soldering iron temperature meter.

Initial testing showed max temperature of my iron tip in the rounds of 180C, it takes also a little to overcome thermal inertia and I guess needs calibration since the melting point  of 60/40 solder (used) is 188C and probe was showing 181.
Other methods of calibration could include freezing and boiling water.

Here's the prototype:

Reading the soldering iron temperature (not exactly a scientific grade measurement):

The code used (changed from the library example)  with output on serial port:
// this library is public domain. enjoy!
//name=MAX6675 library
//sentence=Arduino library for interfacing with MAX6675 thermocouple amplifier
//paragraph=Arduino library for interfacing with MAX6675 thermocouple amplifier


int thermoDO = 4;
int thermoCS = 5;
int thermoCLK = 6;

MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

void setup() {

void loop() {


I also measured using the built in sensor/thermocouple on a JBC type C245 tip showing different values from the K thermocouple included with the MAX6675 module (also not a good idea to use simple wires from the probe to the chip).

 Here's measuring the solder melting point (or higher than that, due to thermal inertia)

Check the size difference between the Maplin "garden variety" type soldering iron and the C245 from JBC. Bellow also an example on how small the JBC tip is:

...and no, I didn't bought the full station, just one tip to "play" around. Looks nice but hard to justify the price and I guess the tip's won't last as long as regular heating element's.

Connection to the Arduino (I used the "nano") from the MAX6675 module is as follow:

DO = pin Digial 4 (D4)
CS = pin Digital 5 (D5)
CLK = pin Digital 6 (D6)

Interesting the module I got has the wrong polarity for the thermocouple printed on the board, that is; one side of PCB shows "+" the oposit side shows "-", If you connect wrongly the thermocouple, the temperature output from the code will show decreasing when it's getting warm and also near freezing point at room temperature (assuming you are not in the north pole doing experiments.....)

Have a great season.


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