K type Thermocouple/Uno/MAX31855 query

Other Hardware Sensors
1

Absolute newbie – so please pardon my incorrect terminology. Trying to understand what I need to do here to read a temp.

Platform: Arduino Uno
Amp: MAX 31855
Thermocouple: K type thermocouple
All products from adafruit.

Have read the information posted related to the above products - but seem to be missing something in the hookup:
MAX31855 amplifier has 6 pins labeled thusly:
-> Vin
<- 3Vo
-> GRD
<- DO
-> CS
-> CLK

Thermocouple connected to terminal posts by color.

Instructions indicate that VCC goes to 3-5 V, and that GND goes to GND. Additionally, it indicates that 3 connections are to be made to 3 digital pins of the Uno.

From the layout, it does not appear that the MAX 31855 can “plug directly into” the UNO (as per a shield) – pin arrangement does not seem to line up.

If I am incorrect here – please advise. If not, allow me to continue.

Assuming the connections are to be made via a breadboard, I proceeded down that avenue, with the UNO plugged into the desktop via USB.

MAX31855 UNO
Vin <-> UNO 5V
3Vo Nothing here
GND <-> UNO GRN
DO <-> UNO Pin 8
CS <-> UNO Pin 9
CLK <-> UNO Pin 10

Uploaded the MAX31855 text via the Arduino interface, then opened the serial monitor.

Could see the MAX31855 initialize then begin its cycle with the following readout:

MAX31855 test
Internal Temp = 0.00
C = 0.00
Internal Temp = 0.00
C = 0.00
Internal Temp = 0.00
C = 0.00
Internal Temp = 0.00
C = 0.00
etc

Again – I am in the very early stages of trying to learn this. Any comments, suggestions, corrections would be most appreciated.

Thanks!

keninar

2

Hi,
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The MAX31855 datasheet clearly states the part is 3.3v with an 'Absolute Maximum' rating of 3.6v..., you may have already blown the ic I'm sorry to say.

3

Cy, he's using the Adafruit breakout which has a 3V regulator onboard.

keninar, can you post your code?

4

this may come a little late, however for what its worth: like the before mentioned, must use 3.3v, on the 31855 . BUT there is a catch though! the catch is: the max31855 uses 3.3v LOGIC and the UNO uses 5v logic. in other words you can/WILL "lockout" your Microprocessor. i "locked out" 2 MCU's before i figured it out. :frowning: the solution is to power the MCU at 3.3v if you can, so the logic levels are the same. the other solution is to use a TXB0104 level translator.

good luck.