I2C - I need a 1 second delay between sending byte and reading reading data from sensor

Question

I am using an Atlas Scientific I2C sensor and trying to connect it to the Pi. http://www.atlas-scientific.com/_files/_datasheets/_circuit/EC_EZO_Datasheet.pdf

Here's the code that I'm running:

import smbus
import time
bus = smbus.SMBus(1)
def read_sensor(addr):
 bus.write_byte(addr,0x52)
 time.sleep(1) # This is required by the sensor
 for i in range (0,32):
 print bus.read_byte(addr)

I also try:

result = bus.read_i2c_block_data(addr,0x52)
print result # returns 1, then 255's

When I write 0x52, the light changes as it should, then when I read a byte, the first byte is 1, meaning that it is successful, but the rest of the bytes are 255.

How can I trigger the read by sending 0x52, then wait a second while the sensor takes its readings, the read the 32 bytes available WITHOUT sending any additional commands.

I looked into pyA13 library, but this apparently doesn't run on Pi.

Can Python do this?

• tlhIngan: Isn't your Python script already doing the 1 second pause? Did you calibrate the sensor first? Did you try using the sensor in different environments?
• pekasus: @tlhIngan It is pausing, but I think the problem is that when I call the read, it is sending a new request to the sensor causing the sensor to think it is a new request
• joan: You aren't talking to the device. write_byte(0x09, 0x52) is sending byte 0x52 to (the non-existent) device at address 0x09.
• pekasus: @joan 0x09 is the actual address of the sensor. I forgot to replace it with 'addr' when I pasted the code. I corrected it.

Answer 1

I think you may be running up against an inherent problem with SMBus commands, they are not great at talking to I2C devices.

I suggest you try reading the device with my pigpio library.

If you have a recent Raspbian this may be preinstalled or available from the repositories.

To check try

sudo pigpiod

If that doesn't work do

sudo apt-get update
sudo apt-get install pigpio python-pigpio python3-pigpio

and then do sudo pigpiod

If that doesn't work see http://abyz.me.uk/rpi/pigpio/download.html

Then enter the following commands

pigs i2co 1 0x09 0
pigs i2cwd 0 0x52
sleep 1
pigs -x i2crd 0 20

If that gives a result you can do the same with the pigpio Python module.

• pekasus: This looks promising. I tried it on Ubuntu Mate, and it can't find the packages in apt-get. I'll try it on my Raspian later.