Cannot get MAX 31855 readings

[Cadius]

I'm obviously doing something stupid and have beat my head against the metaphorical wall about as much as I can.

I've bought several MAX31855 breakout boards. I'm trying to get them to work, using the example included with the Adafruit_MAX31855 library, only changing the pin numbers to match my environment. I've tried this code on two Arduino Megas and with three MAX31855 boards and with different wiring at least 3 times. I'm using the 5v and Gnd pins at the ends of the pins 22 - 53 block for power, 35 for CLK, 37 for CS, and 39 for DO. I'm using the MAX library dated 6/15/2012.

I get 4.6v at the Arduino and at the MAx board, so I know power is getting to the boards.
I get 3.3v from the 3Vo pin at the Max board.
I get 2.2v from the DO pin at the Max board.
I get 4.5v from the CS pin at the Max board.
I get 4.5v from the CLK pin at the Max board.
I get fluctuating readings around 2.5v from the Thermocouple wires.

The example code just publishes 0.00 for both internal and KC temps.

Any idea what I'm doing wrong here?

Max31855.png (941.49 KiB) Viewed 2258 times

[adafruit_support_bill]

Can you post the code you are using? Also a close-up of your solder connections.

I get fluctuating readings around 2.5v from the Thermocouple wires.

That doesn't sound right at all. The output from a T/C is in the microvolt range.

[Cadius]

Code: Select all

/***************************************************
  This is an example for the Adafruit Thermocouple Sensor w/MAX31855K

  Designed specifically to work with the Adafruit Thermocouple Sensor
  ----> https://www.adafruit.com/products/269

  These displays use SPI to communicate, 3 pins are required to 
  interface
  Adafruit invests time and resources providing this open source code,
  please support Adafruit and open-source hardware by purchasing
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries. 
  BSD license, all text above must be included in any redistribution
****************************************************/

#include "Adafruit_MAX31855.h"

int thermoDO = 39;
int thermoCS = 37;
int thermoCLK = 35;

Adafruit_MAX31855 thermocouple(thermoCLK, thermoCS, thermoDO);
 
void setup() {
  Serial.begin(9600);
 
  Serial.println("MAX31855 test");
  // wait for MAX chip to stabilize
  delay(500);
}

void loop() {
  // basic readout test, just print the current temp
   Serial.print("Internal Temp = ");
   Serial.println(thermocouple.readInternal());

   double c = thermocouple.readCelsius();
   if (isnan(c)) {
     Serial.println("Something wrong with thermocouple!");
   } else {
     Serial.print("C = ");
     Serial.println(c);
   }
   //Serial.print("F = ");
   //Serial.println(thermocouple.readFarenheit());

   delay(1000);
}


IMG_20120629_091021.jpg (185 KiB) Viewed 2251 times

[adafruit_support_rick]

Let's try to rule out some other things as well.
First of all, it looks like you've got some other stuff attached to the mega. Remove any other devices, so we can just focus on the MAX31855.
Which model/revision of the MEGA are you using?
Have you tried different locations on the breadboard?
Have you tried connecting the MAX31855 board directly to the MEGA - i.e., no CAT5, no breadboard?
Have you tried it with the thermocouple disconnected, to just access the internal temp?
Have you tried using the standard SPI pins 51 52 and 53?
Are you certain you've got the correct board-type selected for your sketch?
Have you changed anything else in the example sketch other than the pin numbers? Maybe start with a fresh copy, just to make sure.
Do you have a UNO available to try this with?

[Cadius]

I'm using two Mega R3's

I haven't tried the direct link yet.For that, make the 5v pin a pinMode(..., OUTPUT) and the GND and Vo pins as pinMode(..., INPUT) right?

I did just take out the Cat5 cabling. Using jumpers directly from 51-53 (and 5v/gnd) to breadboard, I get either 0.00/0.00 OR -127.94 internal and "Something wrong with the thermocouple!" depending on which Max41855 board I try -- two give the -127, one gives 0.00.

Connecting or not connecting the TC seems to make no difference.

My sketch says Arduino Mega 2560 or Mega ADK.

I've tried with a fresh copy of the library / example from the same Zip. No change. No, I've only changed the pin assignments.

I have the two Megas, but no other Arduinos.

[adafruit_support_bill]

I did just take out the Cat5 cabling. Using jumpers directly from 51-53 (and 5v/gnd) to breadboard, I get either 0.00/0.00 OR -127.94 internal and "Something wrong with the thermocouple!" depending on which Max41855 board I try -- two give the -127, one gives 0.00.

Sounds like you are getting closer - but still have some intermittent connections. The solder photo is a little fuzzy to see well. But try re-touching those joints. Make sure they are smooth and shiny - and that the solder flows well onto both the wire and the solder pad.

[Cadius]

I redid the solders; making sure to completely cover the solder pad on both top and bottom. Smooth/shiny.
Still get 0.00 / 0 readings.

[adafruit_support_bill]

Are you seeing that on all three boards now?

[adafruit_support_rick]

I haven't tried the direct link yet.For that, make the 5v pin a pinMode(..., OUTPUT) and the GND and Vo pins as pinMode(..., INPUT) right?

You shouldn't be using I/O pins for power and ground. Just take the wires you've already soldered onto the MAX31855 and connect the clock and data pins to 35, 37, and 39 as have been doing, Vin to a +5V socket on the MEGA, and GND to a GND pin on the MEGA.

[Cadius]

Using soldered wire for Gnd and Vin and using pins straight into the Arduino 47, 49, and 51, I still get 0.00 readings from internal and 0 from TC even with no TC wire connected.

This has completely thrown me.

[adafruit_support_bill]

Are you seeing that on all three boards now? Before you were getting different results with two of them.

[Cadius]

I've tried the direct-pin connection with two boards; one of those boards has never been attached to anything (just in case my attempts at getting this thing working somehow fried the other boards.)

I've also tried moving from the GND and 5v pins on the 22 - 53 block to the 5v/Gnd pins on the ethernet shield, and the 3.3v/Gnd pins on the ethernet shield.

Still get 0/0.00 on those attempts.

[adafruit_support_rick]

Ethernet shield? You should disconnect EVERYTHING from the MEGA until we figure out what's up with the MAX31855.

[Cadius]

Pulled the Ethernet shield.

Same response from two MAX31855 boards: 0.00 / 0.

I get no difference even if I remove the Vin line; it's like the module isn't communicating at all.

[Cadius]

Anything else I can try?
[list=]
[*]I've tested using the example code from the Max31855 library with seven different MAX breakout boards.[/*]
[*]I've tested with two Arduino MEGA 2560 R3's.[/*]
[*]I've tried compiling the example project under both the 1.0.1 and 1.0 Arduino IDE.[/*]
[*]I've tried with direct pins, multiple different sets of wires, with/without a breadboard, and with resoldered pins.[/*]
[*]I've tried with and without a TC wire connected.[/*]
[*]I've redownloaded the Max31855 library today, just to make sure I had a clean install there.[/*]
[/list]

Quite frankly, I have no idea what else to even think about trying. All I get is 0.00 and 0 readings.

I had nothing like this kind of problem with the Max6675 boards. But they won't read the ultra-low temps I need (and have been discontinued...).

I'm stumped. And frustrated.