I2C pressure sensor with Labview and U6 | LabJack
 
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I2C pressure sensor with Labview and U6

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User79
marc.legree's picture
I2C pressure sensor with Labview and U6

Hello,

I am using Labview 16 with a Labjack U6 to communicate with a pressure sensor (LMI). When running my program I don't get any error message but I am not getting measures from the sensor.

Here are a few infos on my setup :

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- Pin 5, 6 and 3 of the sensor are connected to the labjack Ground => 7-bit I2C address is 1011100 (0x5C) (page 8/17). After the shifting, the 8 bit address that I use in my code is 10111000

- AO0 is set to 3.3V. The VS input of the sensor is connected to the AO0 output for powering. Cheked the voltage on the sensors pins, it’s ok.

- A 4.7kOhms resistance is connected between SDA pin  and Vs.

- A 4.7kOhms resistance is connected between SCL pin  and Vs.

The data sheet of the sensor explaining how to communicate with the sensor can be fined here : https://www.first-sensor.com/cms/upload/datasheets/DS_Standard-LMI_E_118...

I have attached a Labview 8.0 version of the program. And also 2 print screens of the program in case you can't open it.

Can you see what I am doing wrong?

Thank you very much.

Best regards,

User

LabJack Support
LabJack Support's picture
I am not able to open your VI

I am not able to open your VI, but I do see a couple potential issues in the block diagram screenshots. The first is that the IO lines are set to 0 and 1. We recommend using EIO for serial communication because it has less impedance. The second issue is that the speed is set to zero, it is usually a good idea to start with the clock speed set low and the raise it after everything is working. 10 kHz is a good starting place. The lower clock speed may also help when using FIO lines.

Also, have a look at our I2C app-note. It contains a lot of good advise that will help you avoid common I2C pitfalls. The acknowledgement reporting may be useful.

If that doesn't help we may need an oscilloscope or logic analyzer. 

User79
marc.legree's picture
Hello,

Hello,

I have switched over to the EI00 and EI01 pins, and set the speed to the lowest value (255) but I still don't get any measures back. 

There could be some clock streching or other subtilities that may take too much time for me to solve.

I will look for other solutions.

Thank you for your help.

User

LabJack Support
LabJack Support's picture
Did you check the

Did you check the acknowledgements (LJ_chI2C_GET_ACKS)?

That will tell you if the slave device is respond at all. If not problems are likely hardware or the address value. If it is responding to its address then our problem is in the usage of the slave device.

User79
marc.legree's picture
Hi,

Hi,

When running the program (screenshot) I get Numbers of Ack's = 3 at the first loop (but no measures) . After first loop, it changes to 0 (no measures).

I got a second pressure sensor that runs ok with Arduino. The program is really simple, for each loop :

I  send the sensor's address : 0x5c

I send the 0x20 command to tell the sensor to make a measurement

I ask for a 2 bytes read

I have attached the VI in 8.0 version in case you succeed in opening it.

File Attachment: 
LabJack Support
LabJack Support's picture
The Acks is good news. That

The Acks is good news. That means that both the address and the command byte were acknowledged.

Looking at the VI diagram, I think we need to move GET_ACKS to a separate call after the the add-go-get that runs LJ_chI2C_WRITE and LJ_chI2C_READ. The driver might be correcting that for us, but I am not sure.

If that doesn't help we can try the compatibility options. Try changing the options byte to:

  1. LJ_chI2C_OPTIONS = 4 - Changes the way the bus is switched from write to read
  2. LJ_chI2C_OPTIONS = 8 - Enables clock stretching, which allow a slave device to delay the clock signal if it needs more processing time.
  3. LJ_chI2C_OPTIONS = 12 - Uses both of the above options.

User79
marc.legree's picture
Hello,

Hello,

Your advice worked out, thanks a lot!

It's now working with the setup that you can see on the screen shot (Get_acks moved as a seperate call and Options set to 12). If Get_acks is not moved, changing the options doesn't make things work.

I have two other questions : 

1) I don't understand how Get acks adds up the Acks, since when ?

- If Get_Acks is not a seperate call, I get no measurement but  get Acks = 3

- if I call Write then Get_Acks at the time and Read separately, I get the correct measurements, and get acks = 3

-if only Get_Acks is seperate, I get the correct measurements and get acks = 1

2/I have put 4 of these sensors (each have their own adddress) on line EI0 and EI1

   I have put 4 of these sensors (each have their own adddress) on line EI2 and EI3

I was planning to get the measurement of those two I2C pair of  lines in parrallele. Can you confirm it is not possible? When doing that, I only get measurement from one pair of lines. the other one outputs the measurements from the other pair.

Thanks.

User

File Attachment: 
LabJack Support
LabJack Support's picture
1) Every transmitted byte is

1) Every transmitted byte is represented by a bit in the ACK array. A 3 in binary is 0b00000011, which would mean that two bytes were acknowledged.

"If Get_Acks is not a seperate call..." The Get_Acks was between the transmit and receive operations. So, I think the request to read ACKs was terminating the I2C operation before the reads could run. Separating out the read and write operations would would because that would run two separate I2C operations one to write and one to read. 

2) The U6 can run multiple I2C buses. The only limitation is that only one can be actively clocking at any give time.