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Forum Index : Microcontroller and PC projects : Reading thermocouples.
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| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Ok, Preamble first. I used to have an old Pot Belly heater in the outdoor area; It's air vent at the bottom was operated by a bimetallic coil to regulate the air flow. Worked brilliantly. So, Thinking of controlling the air damper on my main heater; Eliminate all the trips up & down to adjust it's air flow. I've got a couple of MAX6755 Thermocouple modules & can see how the data string looks.....  I can probably deal with pulling that apart & getting the data. What I'm not clear on is SPI communications & how I get the 2 bytes from the device. I know CS has to be pulled low??, will something like the example code in the manual be all I need to retrieve the 2 bytes? [Code]PIN(10) = 1 : SETPIN 10, DOUT ' pin 10 will be used as the enable signal SPI OPEN 5000000, 3, 8 ' speed is 5 MHz and the data size is 8 bits PIN(10) = 0 ' assert the enable line (active low) junk = SPI(&H80) ' send the command and ignore the return byte1 = SPI(0) ' get the first byte from the slave byte2 = SPI(0) ' get the second byte from the slave PIN(10) = 1 ' deselect the slave SPI CLOSE ' and close the channel[/code] Thanks Phil. Module I'm using.  |
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Justplayin Guru Joined: 31/01/2014 Location: United StatesPosts: 313 |
SPI is not mentioned in the data sheet for the MAX6755, is the board an SPI adapter? does it have separate docs? --Curtis I am not a Mad Scientist... It makes me happy inventing new ways to take over the world!! |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
I would have read SPI on this data sheet. Phil. |
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redrok Senior Member  Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi CurtisSee:Henrysbench See:MAX6675 Datasheet It seems to say its got SPI. I've been using the MAX31855 which seems to work similarly and the SPI works for me. redrok |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3167 |
Reading from the chip is simple. You can read the whole 16 bits in one lump: PIN(10) = 1 ' set the pin to inactive SETPIN 10, DOUT ' pin 10 is the enable signal SPI OPEN 100000, 3, 16 ' speed is 100KHz, data size is 16 bits PIN(10) = 0 ' assert the enable line (active low) d = SPI(0) ' get the whole 16 bits PIN(10) = 1 ' deselect the chip SPI CLOSE ' close the SPI channel The data will be in d (preferably this is an integer). PRINT "Thermocouple reading =" d>>3 Because this is a type K thermocouple you can get away with treating its output as linear from 0 to 1000 C. So this should be accurate within a few degrees: PRINT "Temperature =" d>>5 " degrees C" I have not tested this but it should work. Geoff Graham - http://geoffg.net |
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Zonker Guru Joined: 18/08/2012 Location: United StatesPosts: 761 |
Hey Phil... I use 2 of the MAX31855 IC's in the "round gauge" projects and seems to work well.. Here is the read "snippet" of code... Its taken from the whole main program, so you will need to do the pin init stuff for your hardware.. ' the init stuff.. Pin(42)=1 ' set IC4 CS pin high - (deselected) SetPin 42,dout ' CS pin for IC4 MAX31855 thermocouple chip SPI open 10000,1,32 ' 10k bits speed, data on falling edge, 32bit transfer ' from somewhere inside the main loop.. read_IC4 If Not temp2_error Then temp2_avarge=temp2_avarge*0.9 temp2_avarge=temp2_avarge+temp2_F/10 Print Cint(temp2_avarge); Print temp2_avarge; Print temp2_C g2_val=Cint(temp2_avarge)+gauge2_offset EndIf ' later on in the "subs" section.. Sub read_IC4 Pin(42)=0 ' set IC4 CS pin low - (selected) temp2_data=SPI(0) Pin(42)=1 ' set IC4 CS pin high - (deselected) temp2_error=temp2_data And &B111 ' mask for error codes (bit D3 Reserved =0) If temp2_error Then Select Case temp2_error Case 1 ' probe open If Not IC4_err_onscreen Then Text 110,150," ",cm,3,1,RGB(black) Text 110,140,"Sensor",cm,2,1,RGB(yellow),RGB(red) ' error msg Text 110,160,"Open",cm,2,1,RGB(yellow),RGB(red) ' error msg EndIf Case 2 ' probe gronded If Not IC4_err_onscreen Then Text 110,150," ",cm,3,1,RGB(black) Text 110,140,"Sensor",cm,2,1,RGB(yellow),RGB(red) ' error msg Text 110,150,"Ground",cm,2,1,RGB(yellow),RGB(red) ' error msg EndIf Case 4 ' probe on VCC If Not IC4_err_onscreen Then Text 110,150," ",cm,3,1,RGB(black) Text 110,140,"Sensor",cm,2,1,RGB(yellow),RGB(red) ' error msg Text 110,1600,"Supply",cm,2,1,RGB(yellow),RGB(red) ' error msg EndIf Case Else ' IC is not connected If Not IC4_err_onscreen Then Text 110,150," ",cm,3,1,RGB(black) Text 110,140,"IC Not",cm,2,1,RGB(yellow),RGB(red) ' error msg Text 110,160,"Found",cm,2,1,RGB(yellow),RGB(red) ' error msg EndIf IC4_err_onscreen=1 ' store err msg state End Select Else temp2_internal=temp2_data>>4 And &B111111111111 ' mask for DIE temp (no fault bit) temp2_ex_quarters=temp2_data>>18 And &B11 ' mask for .25 of degree (D17 Reserved=0) temp2_ex_quarters=temp2_ex_quarters*.25 temp2_external=temp2_data>>20 temp2_external=temp2_external+temp2_ex_quarters temp2_C=temp2_external temp2_F=temp2_C*9/5+32 IC4_err_onscreen=0 ' store err msg state EndIf End Sub I take in the data as 32 bit all at once and then do the shifting to "cut it up" into the different parts... I also check the internal DIE temp and error bits... Hope this helps..!  |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3167 |
Zonker, why read 32 bits? As far as I can see the MAX6675 provides 16 bits of data. EDIT: It might be because Phil's module is using a MAX6675 while you were using a MAX31855 ???? MORE EDIT: On rereading the MAX6675 data sheet, I believe that the SPI open should be: SPI OPEN 100000, 2, 16 ' speed is 100KHz, data size is 16 bits ie, sample on the falling clock edge Geoff Geoff Graham - http://geoffg.net |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Thanks Geoff, Will give it a try later.... About to enjoy a beer after the hair tearing. Interesting, I did look at both the MAX6675 & MAX31855, not sure what lead to the final decision, they were ordered 2 weeks back. Phil. |
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