need .py code for reading Max31855 A/D temp converter

While I don't have that particular module I went to the Adafruit site and checked it out. It looks like it is a simple SPI device.

Check here for python instructions Simple SPI on Raspberry Pi - 100RandomTasks

From Adafruit's arduino example it looks like to read celsius temperature, you do a 32 bit read of the SPI data, shift right 18 bits and multiply by .25 and you've got celcius temperature.

https://github.com/adafruit/Adafruit-MAX31855-library/blob/master/Adafruit_MAX31855.cpp

You'll be surprised at how easy this really is.

Good luck,

Mike

Edited bad link

Taking a second look at the RasPi SPI library, you may have to make your own 32 bit read, but everything is in the .cpp file linked above.

Take a stab at it, if you can't figure it out, post your code here and we can suggest some fixes.

Mike

Thanks Michael, I will take a stab at it. I am assuming that the .ccp code is similar to the .py code.

There are definitely syntactical differences between the 2, but the ideas will be similar.

The Adafruit example is good because she commented out alot of the fluff. It is really simplified to show only what is necessary.

Like I said, give it a stab, just a simple read from the device, there are plenty of folks on here who are willing to help debug code.

Mike

You can even compile that code to work with the raspberry with the arduPi library Cooking Hacks - Documentation - Raspberry Pi to Arduino shields connection bridge or may be with the WiringPi library.

You just will need to add a main() function as entry point for you progra, initialize one Adafruit_MAX31855 instance and call the readCelsius() or readFarenheit() methods.

There is one thing I would double check before to connect it, from the description you can read "This breakout board has the chip itself, a 3.3V regulator with 10uF bypass capacitors and level shifting circuitry". Take care, the Raspberrry is a 3.3V device itself, you don't need level shifting at all.

Before to start I would input 3.3V in both VIN and V3.3 and check if the output is 3.3V or you risk a fried Pi.

Thanks Michael, I will take a stab at it. I am assuming that the .ccp code is similar to the .py code.

Thanks Iago for the info. I will look into these things.

Don

I found this code from Tuckie on Github and am trying to use it and having problems:
https://github.com/Tuckie/max31855/blob/master/max31855.py
I am using only one chip so how much of the
bottom few lines of the code can I eliminate since that is
where one of the errors seems to be comming from?

Another error is comming from line 39. I am using the SPI
pins as follows:
sclk- GP11
miso- GP9
cs-   GP8
3.3v from buss on Gert board
gnd  from buss on Gert board

I don't understand how the code knows where to find these pins
and assign them correctly and I don't see lines to input them.
I have very limited knowledge on how to read this code but it looks like the pins are being initlized
in lines 9 thru 32. please explain!

following is the error message I got when I ran the code:

Python 2.7.3 (default, Jan 13 2013, 11:20:46)

[GCC 4.6.3] on linux2

Type "copyright", "credits" or "license()" for more information.

>>> ================================ RESTART ================================

>>>

Traceback (most recent call last):
  File "/home/pi/read_display  Max_31855 thermocouple_amp.txt", line 176, in <module>
 
  thermocouples.append(MAX31855(cs_pin, clock_pin, data_pin, units))

  File "/home/pi/read_display  Max_31855 thermocouple_amp.txt", line 39, in __init__
 
  GPIO.setup(self.cs_pin, GPIO.OUT)
RuntimeError: No access to /dev/mem.  Try running as root!
>>>

entire list of code follows, Thank you Tuckie:

#!/usr/bin/python
import RPi.GPIO as GPIO

class MAX31855(object):
    '''Python driver for [MAX38155 Cold-Junction Compensated Thermocouple-to-Digital Converter](http://www.maximintegrated.com/datasheet/index.mvp/id/7273)
     Requires:
     - The [GPIO Library](https://code.google.com/p/raspberry-gpio-python/) (Already on most Raspberry Pi OS builds)
     - A [Raspberry Pi](http://www.raspberrypi.org/)

    '''
def __init__(self, cs_pin, clock_pin, data_pin, units = "c", board = GPIO.BCM):
        '''Initialize Soft (Bitbang) SPI bus

        Parameters:
        - cs_pin:    Chip Select (CS) / Slave Select (SS) pin (Any GPIO) 
        - clock_pin: Clock (SCLK / SCK) pin (Any GPIO)
        - data_pin:  Data input (SO / MOSI) pin (Any GPIO)
        - units:     (optional) unit of measurement to return. ("c" (default) | "k" | "f")
        - board:     (optional) pin numbering method as per RPi.GPIO library (GPIO.BCM (default) | GPIO.BOARD)

        '''
        self.cs_pin = cs_pin
        self.clock_pin = clock_pin
        self.data_pin = data_pin
        self.units = units
        self.data = None
        self.board = board

        # Initialize needed GPIO
        GPIO.setmode(self.board)
        GPIO.setup(self.cs_pin, GPIO.OUT)
        GPIO.setup(self.clock_pin, GPIO.OUT)
        GPIO.setup(self.data_pin, GPIO.IN)

        # Pull chip select high to make chip inactive
        GPIO.output(self.cs_pin, GPIO.HIGH)

    def get(self):
        '''Reads SPI bus and returns current value of thermocouple.'''
        self.read()
        self.checkErrors()
        return getattr(self, "to_" + self.units)(self.data_to_tc_temperature())

    def get_rj(self):
        '''Reads SPI bus and returns current value of reference junction.'''
        self.read()
        return getattr(self, "to_" + self.units)(self.data_to_rj_temperature())

    def read(self):
        '''Reads 32 bits of the SPI bus & stores as an integer in self.data.'''
        bytesin = 0
        # Select the chip
        GPIO.output(self.cs_pin, GPIO.LOW)
        # Read in 32 bits
        for i in range(32):
            GPIO.output(self.clock_pin, GPIO.LOW)
            bytesin = bytesin << 1
            if (GPIO.input(self.data_pin)):
                bytesin = bytesin | 1
            GPIO.output(self.clock_pin, GPIO.HIGH)
        # Unselect the chip
        GPIO.output(self.cs_pin, GPIO.HIGH)
        # Save data
        self.data = bytesin

    def checkErrors(self, data_32 = None):
        '''Checks error bits to see if there are any SCV, SCG, or OC faults'''
        if data_32 is None:
            data_32 = self.data
        anyErrors = (data_32 & 0x10000) != 0    # Fault bit, D16
        noConnection = (data_32 & 1) != 0       # OC bit, D0
        shortToGround = (data_32 & 2) != 0      # SCG bit, D1
        shortToVCC = (data_32 & 4) != 0         # SCV bit, D2
        if anyErrors:
            if noConnection:
                raise MAX31855Error("No Connection")
            elif shortToGround:
                raise MAX31855Error("Thermocouple short to ground")
            elif shortToVCC:
                raise MAX31855Error("Thermocouple short to VCC")
            else:
                # Perhaps another SPI device is trying to send data?
                # Did you remember to initialize all other SPI devices?
                raise MAX31855Error("Unknown Error")

    def data_to_tc_temperature(self, data_32 = None):
        '''Takes an integer and returns a thermocouple temperature in celsius.'''
        if data_32 is None:
            data_32 = self.data
        tc_data = ((data_32 >> 18) & 0x3FFF)
        return self.convert_tc_data(tc_data)

    def data_to_rj_temperature(self, data_32 = None):
        '''Takes an integer and returns a reference junction temperature in celsius.'''
        if data_32 is None:
            data_32 = self.data
        rj_data = ((data_32 >> 4) & 0xFFF)
        return self.convert_rj_data(rj_data)

    def convert_tc_data(self, tc_data):
        '''Convert thermocouple data to a useful number (celsius).'''
        if tc_data & 0x2000:
            # two's compliment
            without_resolution = ~tc_data & 0x1FFF
            without_resolution += 1
            without_resolution *= -1
        else:
            without_resolution = tc_data & 0x1FFF
        return without_resolution * 0.25

    def convert_rj_data(self, rj_data):
        '''Convert reference junction data to a useful number (celsius).'''
        if rj_data & 0x800:
           without_resolution = ~rj_data & 0x7FF
           without_resolution += 1
           without_resolution *= -1
        else:
             without_resolution = rj_data & 0x7FF
        return without_resolution * 0.0625

    def to_c(self, celsius):
        '''Celsius passthrough for generic to_* method.'''
        return celsius

    def to_k(self, celsius):
        '''Convert celsius to kelvin.'''
        return celsius + 273.15

    def to_f(self, celsius):
        '''Convert celsius to fahrenheit.'''
        return celsius * 9.0/5.0 + 32

    def cleanup(self):
        '''Selective GPIO cleanup'''
        GPIO.setup(self.cs_pin, GPIO.IN)
        GPIO.setup(self.clock_pin, GPIO.IN)

class MAX31855Error(Exception):
     def __init__(self, value):
         self.value = value
     def __str__(self):
         return repr(self.value)

if __name__ == "__main__":

    # Multi-chip example
    import time
    cs_pins = [4, 17, 18, 24]
    clock_pin = 23
    data_pin = 22
    units = "f"
    thermocouples = []
    for cs_pin in cs_pins:
        thermocouples.append(MAX31855(cs_pin, clock_pin, data_pin, units))
    running = True
    while(running):
        try:
            for thermocouple in thermocouples:
                rj = thermocouple.get_rj()
                try:
                    tc = thermocouple.get()
                except MAX31855Error as e:
                    tc = "Error: "+ e.value
                    running = False
                print("tc: {} and rj: {}".format(tc, rj))
            time.sleep(1)
        except KeyboardInterrupt:
            running = False
    for thermocouple in thermocouples:
        thermocouple.cleanup()

Hey Don, good to see you are trying

First thing, cs_pins = [4, 17, 18, 24]

bring that array down to one element, that is how many thermocouples you are using

I think you want to change it to:

cs_pins = [24]

second change:

clock_pin = 23

data_pin = 21

and give that a shot

Mike

Going by this page:

RPi Low-level peripherals - eLinux.org

in the Python section

# use P1 header pin numbering convention

GPIO.setmode(GPIO.BOARD)

That would give you the pins as above, it looks like he defaults to GPIO.BCM, you could hardcode GPIO.BOARD into the code, where he does the set mode, or you can pass that in, or figure out the BCM equivalents.

Also, the error about running as root, run it as root by doing

sudo <commandname>

Mike