Read value from SRF02 sensor

[ewok2]

Hello
Trying to read the distance from a SRF02 sensor with I2C.
I am on a RP2040 zero board

The datasheet of SRF02 is there : srf02_i2c.pdf

I try the folowing code :

import time
from machine import I2C

i2c_port_num = 1
srf02_address = 117
srf02_sleep = 0.07

i2c = I2C(i2c_port_num, scl=Pin(15), sda=Pin(14))
time.sleep(srf02_sleep)
print(i2c.readfrom_mem(srf02_address,0,6))

and get
b'\x06\x18\x00\x00\x00\x00'

it seems it works as it is not null but I expect distance in the byte 2 and 3.
And there where an obstacle in front of the sensor 50cm forward...

Where am i wrong?

Thnaks for help

[ewok2]

I succed to use this sensor on a raspberry PI with

import smbus, time
i2c = smbus.SMBus(1)
i2c.write_byte_data(0x75, 0, 81) 
dst = i2c.read_word_data(adresse, 2) 

Any idea of the smbus specificity compare with the micropythonI2C lib ?

[ewok2]

Some more news, I have perform a test on raspberry with the same sensor :
Raspberry with smbus :
i2c.read_word_data(0x75, 2)
=> 10240
(to get it in centimeter the calculation is "i2cB.read_word_data(0x75, 2)/255" => 40 cm)

Raspberry with low level i2c : read all the sensor range
i2c = pylibi2c.I2CDevice('/dev/i2c-1', 0x75)
i2c.ioctl_read(0x0, 256)
=> bytearray(b'\x06\x18\x00(\x00\x0b\x00\x00\x00\x00\x00\x00\x00&\x04\x00?\t\xdf\x08\x0b\x00\x00\x00\x00\x00\x05\x00%\x8b\x00\x1e7\x9a\xc5\xfbiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii')

Micropython with i2c read
i2c.readfrom_mem(srf02_address,0,256)
=> b"\x06\x18\x00\x00\x00\x00\x00\x00\x00\x00\x05\x00\x00\x00 N\x00\x00\x10'\x00\x00\x00\x00\x00\x00\x05\x00d\x8b\x00\x1fY\x9a\xc5{iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii"

It seem's it works but I have to understand how to convert this sum of hexa to a distance. (and what is the first hexa and last hexo for the distance)

another question... the hexa read is not so "clean" in both low level case..
there are some (,&,?, % in first case
and some space, N, ',Y in second case....

[ewok2]

A result more simple to try to find the way to translate.
I get the bytes one by one and the refult is more clear.
And I get the "word" of the 6 register. (The register that I need to decode are the number 2 and 3 : the first is number 0)

Bytes(hex)	6	18	0	91	0	9	0	0	0	0	0	0	0	 1f	4	0	 f1	20	91	20	9	0	0	0	0	0	5	 1b	 1e	 8b	0	 1e	37	 9a	 c5	 7b

Word (Int)	6150			24			37120			145			2304			9																				

Note1 : if I read after the 35 byte I get 0x7B always
Note2 : If I read after the 6 word I get 0

One strange thing, in the datasheet they are talking about 2 Bytes for the value of the register 2 and 3.
In the smbus code I have found a variable that let think that the register is 3 Bytes.
And I get 36 Bytes for 6 register...

I am lost ;-)