How many thermocouples can I attach to Arduino UNO R3 ?


I am currently busy with a engineering project that requires object surfaces to be kept at constant temperatures inside a wind tunnel. The inside object will contain heating elements and on the outside a thermocouple would be connected.

My idea so far:
The heating element (connected to a relay) should turn on and off depending on the reading the thermocouple obtains.

I am planning to use a MAX31855 thermocouple to digital converter and then a K-type thermocouple.

I need to control the temperatures of a few surfaces (probably 5 ) and would like to know how many surfaces i would be able to control with one arduino board

Thank you

The Adafruit MAX31855 board requires three digital pins (CS, CLK,DO) and you'd need another for a relay to switch on your heating, so four per thermocouple. An Uno has 20 pins available for use as digital I/O, so you could control five surfaces with one.

That would mean that you would have given up use of the serial port for debugging, which would not be desirable.

I suspect though that you could share CS and CLK and if so, the Uno has a more than enough pins available for five surfaces and some debug.

CLK and DO can be shared by all the thermocouple interfaces. CS needs to be separate per thermocouple.


Two Thermocouples to LCD Display
This shows two MAX6675 modules connected to a RoboRED (UNO compatible). A terminal strip has been used to connect the Vcc, GND, CK and SO wires together. There are separate CS (Chip select) wires so the two thermocouples can be read separately.