How to communicate with MLX90614 IR sensor

[tbarania]

The MLX90614 IR sensor communicates using SMBus which requires the Start bit be repeated without a stop bit in between. I saw one posting that looked like PBP that showed the I2CREAD as as working with the 90614.

sensortemp = 0
reg = $07
addr = 0
I2CRead Tda, Tcl, addr, reg, [sensortemp.lowbyte, sensortemp.highbyte]

where reg 7 is the location of the temperature data and addr 0 is the device address.

The I2CREAD command has Control and Address, so maybe Control == addr and Address == reg? What about the repeated Start bit?

[Sherbrook]

8.4.6 of the datasheet shows how to read the temp. So going by this:-

Default slave address is $5A. This is bits 1 to 7 of the first byte. Bit 0 is the read or write bit and as we are writing to the sensor this will be 0. The first byte sent will be $B4 (5A * 2 + 0).

Next byte sent will be $07 the ram address of the data.

Next byte sent will be the read address byte. Bit 0 of the read address is 1 so this will be $B5 (5A * 2 + 1). The PBP command will take care of this and the restart.

The I2C address needs to be a constant. So I would try:-

TEMP VAR BYTE[3]

I2CREAD DataPin,ClockPin,$B4,$07,[STR TEMP\3]

You may also need to add 'DEFINE I2C_HOLD 1'

Best of luck
Phil

[Normnet]

This is snippet from working MLX90614 code (other compiler) to give you a guideline:



Low I2C_SCL_Pin
Low I2C_SDA_Pin

I2C_Start()
I2C_WriteByte($00) 'SLAVE ADDRESS
I2C_WriteByte($07) '$07 = �000111 ADDRESS
I2C_Restart()
I2C_WriteByte($01) 'READ CMD
sdTEMP_C.Byte0 = I2C_ReadByte()
I2C_Ack()
sdTEMP_C.Byte1 = I2C_ReadByte()
I2C_Ack()
yPEC = I2C_ReadByte()
I2C_Stop()

Norm

[Sherbrook]

Have you got 4k7 pullup resistors on the SDA and SCK lines?
What PIC are you using?
Show us your code and schematic and we may be able to help more.
Phil

[tbarania]

After way too much time I got code that works with the MLX90614 temperature sensor. It may not be the most elegant but given the timing required by the SMBus this works.

I wish this sensor would have used the I2C standard. Things would have been a lot easier.




'************************************************* ***************
'* Name : MLX90614_final.BAS
'* Author : Tom Baraniak [email protected]
'* Notice : Copyright (c) 2015 [select VIEW...EDITOR OPTIONS]
'* : All Rights Reserved
'* Date : 4/4/2015
'* Version : 1.0
'* Notes :
'* :
'************************************************* ***************
'
' MLX90614 test using PIC16F688 running at 8MHz
'
'
'

DEFINE OSC 8 '8 MHz clock frequency, others not supported by PBP
define HSER_RCSTA 90h 'enable the serial port receiver
define HSER_TXSTA 24h 'set up the serial port, enable transmit for fast clock
define HSER_BAUD 9600 'select the baud rate, run slow for the RF xmitter
define HSER_CLROERR 1 'automatically clear the buffer overrun error

DEFINE SHIFT_PAUSEUS 20 'slow down the shift in clock or it is too fast for the MLX

reg var word
addr var byte
TLOW var byte
THI var byte
tir var word
j var byte
command var byte
ACK var byte
FIXHI var byte
tempir var word
tout var word


SDA var portc.2
SCL var portc.1
TxD var portc.4
RxD var portc.5 '


CMCON0 = %00000111 'comparator off
OSCCON = %01110111 'runs at 8 MHz internal clock
ADCON0 = %10000000 'ADC is disabled
ANSEL = %00000000 'all digital
TRISA = %11111111 'set up port A where 1 = input, 0 = output
TRISC = %11101001 'set up port C where 1 = input, 0 = output
'
'
'================================================= ================================================== =======================================
'
' IR GROUND TEMPERATURE SENSOR
'
' The RAM address 0x07 contains the linearied object temperature data, low byte first
' The slave address that is the MLX90614 is 0xB4
'
'

sda = 1 'at the start
scl = 1
pause 1000


luup:

hserin 1000, luup, [command]

if command = "B" then 'typing a "B" calls the temperature reading code. This is not part of the MLX code.
call bitbang
endif

goto luup




bitbang:

SDA = 0 'start
pauseus 15 'Can't be too fast so I added some delay. Easier to see on the scope too.
SCL = 0
pauseus 15

'This segment generates salve address B4 1011010x where x is the 8th (unused) bit (actually W). Since W is a 0 anyway the x = 0.
'There may be a more elegant way of sending these 8 bits but this way works and all the timing and sequencing is correct.

sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 0 '0
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 0 '0
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 0 '0
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15

sda = 0
pauseus 15
scl = 1 ' W
pauseus 15
scl = 0
pauseus 15

input sda 'make sda an input for acknowledge A part of sequence
pauseus 15
scl = 1
pauseus 15
scl = 0

pauseus 15
output sda 'make sda an output again to send register 0x07
sda = 0
pauseus 15

for j = 1 to 5 'for/next loop is quick for the 5 leading zeroes
scl = 1
pauseus 15
scl = 0
pauseus 15
next

sda = 1 'for/next loop for the three 1's
for j = 1 to 3
pauseus 15
scl = 1
pauseus 15
scl = 0
next
pauseus 15

input sda 'make sda an input for acknowledge A
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15

output sda 'make sda an output again for S
pauseus 15
sda = 1
pauseus 15
scl = 1
pauseus 15
sda = 0
pauseus 15
scl = 0
pauseus 15


'Like the code for B4 this segment generates B5 1011010x where x is the 8th (unused) bit (actually R). The x=1 (0101 == 5) which R is.
'Again, there may be a more elegant way of sending these bits but this works and the timing and sequence are correct.

sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 0 '0
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 0 '0
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 1 '1
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15
sda = 0 '0
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15

sda = 1
pauseus 15
scl = 1 ' R
pauseus 15
scl = 0
pauseus 15
sda = 0

pauseus 15
input sda 'make sda an input for acknowledge A part of sequence. It remains an input heading into shiftin
pauseus 15
scl = 1
pauseus 15
scl = 0
pauseus 15


shiftin SDA, SCL, 0, [TLOW, ack\1, thi] 'Now we can use the shiftin command to read the 8 least significant bits, the single acknowledge
'bit, and the 8 most significant bits.

tempir = thi * $100 'shifts 8 bits to the left to move this byte to the upper 8 bits of a word
tempir = tempir + tlow 'add the lower byte to the upper byte to make a word


tout = tempir/50 'each bit is .02 degrees K so either multiply by .02 or divide by 50
tout = tout - 273 'subtract 273.15 (to get temperature in degrees C

hserout ["T = ", dec tout, 9, dec tempir, 9, dec THI, 9, dec TLOW, 13]


pause 1000 'added for readability during testing

trisc.1 = 0 'both sda and scl are outputs to reset for the next time thru
trisc.2 = 0

sda = 1 'they both start high
scl = 1
pause 100 'not needed

return


end

[tbarania]

For my previous post I suggest replacing all the "pauseus 15" with:

call wate

And then add the subroutine;
wate:
pauseus 15
return

This should use less compiled code than having to integrate the assembly code for puaseus every time it is needed

[tbarania]

I said in my previous post there is probably a more elegant way to write this code. I used a combination of shiftin and shiftout along with some bit setting and reduced the number of lines of code compared to my previous post.

Feel free to contact me if you have any questions.

This code works for the MLX90614:

'************************************************* ***************
'* Name : MLX90614_shifts.BAS
'* Author : Tom Baraniak [email protected]
'* Notice : Copyright (c) 2015 [select VIEW...EDITOR OPTIONS]
'* : All Rights Reserved
'* Date : 4/5/2015
'* Version : 1.0
'* Notes :
'* :
'************************************************* ***************
'
' MLX90614 test using PIC16F688 at 8MHz
'
' DOES WORK!!!
'

DEFINE OSC 8 '8 MHz clock frequency, others not supported by PBP
define HSER_RCSTA 90h 'enable the serial port receiver
define HSER_TXSTA 24h 'set up the serial port, enable transmit for fast clock
define HSER_BAUD 9600 'select the baud rate, run slow for the RF xmitter
define HSER_CLROERR 1 'automatically clear the buffer overrun error

DEFINE SHIFT_PAUSEUS 20 'slow down the shift in clock

reg var word
addr var byte
templo var byte
temphi var byte
temp var byte[3]
TLOW var byte
THI var byte
sa var byte
sb var byte
sc var byte
sd var byte
tir var word
j var byte
command var byte
ACK var byte
tout var word
TEMPIR var word


SDA var portc.2
SCL var portc.1
TxD var portc.4 'transmitted data - hardware serial port
RxD var portc.5 'received data


CMCON0 = %00000111 'comparator off
OSCCON = %01110111 'runs at 8 MHz internal clock
ADCON0 = %10000000 'ADC is disabled
ANSEL = %00000000 'all digital
TRISA = %11111111 'set up port A where 1 = input, 0 = output
TRISC = %11101001 'set up port C where 1 = input, 0 = output


'================================================= ================================================== =======================================
'
'
' IR GROUND TEMPERATURE SENSOR
'
' The RAM address 0x07 contains the linearied object temperature data, low byte first
' The slave address that is the MLX90614 is 0xB4
'
'


sda = 1 'at the start
scl = 1
pause 1000


luup:

hserin 1000, luup, [command] 'used for testing, not part of the actual MLX code

if command = "B" then
call bitbang
endif

goto luup

'================================================= ================================================== =======================================

bitbang:

SDA = 0 'start
call wate
SCL = 0 'clock idles low
call wate

reg = $07
addr = $B4 'B4 sets W = 0 too
shiftout sda, scl, 1, [addr] 'shift the address B4, 8 bits where LSB is W = 0
'clock idles low mode!!

input sda 'make sda an input for acknowledge A
call wate
scl = 1
call wate
scl = 0
call wate
output sda 'make sda an output again for 07


shiftout sda, scl, 1, [reg] 'register is 07, clock idles low


input sda 'make sda an input for acknowledge A
call wate
scl = 1
call wate
scl = 0

call wate
output sda 'make sda an output again for S
call wate
sda = 1
call wate
scl = 1
call wate
sda = 0
call wate
scl = 0
call wate


addr = $B5
shiftout sda, scl, 1, [addr] 'shift the address B5, 8 bits where LSB is R = 1, clock idles low

call wate
input sda 'make sda an input for acknowledge A part of sequence. It remains an input heading into shiftin
call wate
scl = 1
call wate
scl = 0
call wate


shiftin SDA, SCL, 0, [TLOW, ack\1, thi] 'Now we can use the shiftin command to read the 8 least significant bits, the single acknowledge
'bit, and the 8 most significant bits. clock idles low


tempir = thi * $100 'shifts 8 bits to the left to move this byte to the upper 8 bits of a word
tempir = tempir + tlow 'add the lower byte to the upper byte to make a word


tout = tempir/50 'each bit is .02 degrees K so either multiply by .02 or divide by 50
tout = tout - 273 'subtract 273.15 (to get temperature in degrees C

hserout ["T = ", 9, dec tout, 9, dec tempir, 9, dec THI, 9, dec TLOW, 13]


pause 1000

trisc.1 = 0 'both sda and scl are outputs
trisc.2 = 0

sda = 1 'they both start high
scl = 1
pause 100

return

'================================================= ================================================== =======================================

wate:
pauseus 15 'use a subroutine for the 15 usec dealy - less compiled code
return


end