V1.1 Thermocouple Daughterboard with MAX31855 Chip

gw3d3

I'm working towards the delivery of my first unit to a customer and the deadline is tight. This is my first time using thermocouples on the build. I bought a thermocouple daughterboard V1.1 that was supposed to have the MAX31856 controller, but it does not. It has the MAX31855. This was purchased from PrintedSolid who is an authorized reseller here in the U.S.

I'm using a type "J" Thermocouple that is permanently installed into the heater block so switching to a "K" Type is not an option. Almost no resellers in the U.S./Canada have them in stock and the ones that do are suspect. I ordered one from Ooznest and I'm hoping for the best from DHL Express shipping.

In the mean time I can have one of these by tomorrow.

Would it be possible to fit this to a MB6HC even though the pinout is not the same?

droftarts

@gw3d3 Can you post a picture of your thermocouple board? If it is a v1.1, it should have the MAX31856.

I think the Adafruit MAX31856 thermocouple board should work, but I don't have any experience of wiring it up. Refer to:

The Duet thermocouple daughterboard schematic from https://github.com/Duet3D/TempDaughterboards/blob/master/MAXTempTC/MAXTempTCv1.1.pdf
The 6HC wiring diagram https://docs.duet3d.com/duet_boards/duet_3_mb6hc/duet3_mb_6hc_v1.02_d1.1_wiring.png
The AdaFruit documentation https://learn.adafruit.com/adafruit-max31856-thermocouple-amplifier/
For configuration see https://docs.duet3d.com/User_manual/Connecting_hardware/Temperature_connecting_thermocouples

I think the wires should be:

Adafruit	Duet TempDB connector
Vin	+3.3V (pin 8 )
3Vo	(3.3V output from on board voltage regulator, not connected)
GND	GND (pin 2)
SCK	SPIO_SCK (pin 7)
SDO	SPIO_MISO (
SDI	SPIO_MOSI
CS	spi.cs0 (pin 3)
FLT	(fault, not connected)
DRDY	? (seems not connected)

As it supports a single thermocouple, it only needs one CS pin. Configuration should be something like:

M308 S3 P"spi.cs0"Y"thermocouple-max31856" K"J"; define temperature sensor number 3 as a J Type thermocouple on the first port of a temperature daughter board plugged into the main board.

Ian

gw3d3

@droftarts So, I'm issuing a correction to my original post.

After using the macro lens on my camera to take a picture of the IC I realized it was the correct part number! I switched from a "J" type to a "T" type in my config.g and it seems to be working now.

I was having an issue with an intermittent over/under voltage error but I crimped up another heater assembly and it seems to be stable. Whether or not it was a bad crimp or the actual T.C. I don't know.

I'm using Igus Chainflex shielded cable which is drained to an earth ground. There is about 5" of exposed, but twisted pair lead from where the shielding terminates to the daughterboard. Is this too much?