MAX31855 Thermocouple interface, 1st reading is always double the actual

Other Hardware Sensors
1

Hi,

I have an application that uses a MAX31855K break out board. The unit is stable and reasonably accurate.

However I've found the first reading is always double the actual reading. The 2nd reading on is fine.

Has anyone else seen this?

John

2

My suggestion is to initialize it at the start of your setup code then read it just before you go to the loop.
Good Luck & Have Fun!
Gil

3

Do you use 32-bit MCU?

4

My suggestion is to initialize it at the start of your setup code then read it just before you go to the loop.

I've done that and surprisingly it didn't work..... which did not make sense to me.

Do you use 32-bit MCU?

Yes I'm using a SAMD21 (Arduino M0). Reading SPI.transfer(16) two times.

I've connected a logic analyzer and have found the 1st data bit is not being read. Have to look further. Been delayed by poor solderless board connections. Am going to toss the solderless board.

John

5

UPDATE I found the SPI clock was not as expected. I asked a follow on question under the Network topic.

if interested see SPI issue with MAX31855K

6

Here's the specific thread mentioned by JohnRob (the link above is to the forum section only, which doesn't age well):
https://forum.arduino.cc/index.php?topic=649135