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BGS5T I2C communication and temperature sensors | Thales IoT Developer Community

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Jure's picture
Jure

November 11, 2014 - 9:40am, 9125 views

Hello,

first I would like to ask if anyone tryed to use temperature sensor (IT TMP100, TC74, ...) that uses I2C communication? Does anyone have any recomendation which sensor to use and instructions or code example?

Second thing, is there any tutorial or code example for I2C communication with other devices in Java?

Regards

Jure

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Shaul's picture
Shaul
Nov 11 2014 - 3:34pm

Hi,

I think this example a direction (not temperture but analaog).

https://iot-developer.thalesgroup.com/tutorial/conceptboard-java-multiadc

Jure's picture
Jure
Nov 12 2014 - 10:05am

I am not sure if that is really what I need. But thank you for your help.

I have found TC65i example but I can't find class for i2cConnection:

// Open I2C connection and data streams:
i2cConnection cc = (I2cBusConnection) Connector.open("i2c:0;baudrate=100");
int baudrate = cc.getBaudRate();
InputStream inStream  = cc.openInputStream();
OutputStream outStream = cc.openOutputStream();
 
// Write Transfer Frame, where a = message ID, AE = Slave Address and write 
// request:
String data = "<aAE000102030405060708090A0B0C0E0F>";
outStream.write(data.getBytes(), 0, data.length());
outStream.flush();

But the problem is because there are I2CDAT and I2CCLK. For my sensor I need both, DAT and CCLK. From example I can see how to transmit some data, but how do you change state on DAT and CLK from high to low or the other way?
Here is the protocol of communication:
1. a high-to-low transition of SDA while SCLK is high
How do I set I2CDAT to high?
2. the host must transmit the address byte to the TC74
I can do this step with the example from TC65i
3.Acknowledge (ACK) provides a positive handshake between the host and the TC74. The host releases SDA after transmitting 8 bits. The host then generates a ninth clock cycle to allow the TC74 to pull the SDA line low.
4.After a successful ACK of the address byte, the host must transmit the data byte to be written, or clock-in the data to be read. ACK will be generated upon a successful write of a data byte into the TC74.
5.Communications must be terminated by a STOP condition (a low-to-high transition of SDA while SCLK is high).
Bartłomiej Gemalto Moderator's picture
Bartłomiej Gema...
Nov 12 2014 - 9:17pm

Hello Jure,

You don't change the lines states manually. The i2c protocol is implemented inside. You can only send and receive data.

TC65i module has i2c interface while the TC74 sensor claims to have SMBus/I2C - SMBus is not exactly the same as i2c and the may not be compatible. 

Regards,

Bartłomiej

Jure's picture
Jure
Nov 13 2014 - 9:33am

Hello Bartłomiej,

thank you for your response. I allready ordered the sensor, so I hope that I can get it to work. Can you maybe recomend any other sensor, that was allready used with BGS5T, if I will have problem with this?

Regards

Jure

Jure's picture
Jure
Nov 17 2014 - 11:23am

I connected sensor to module and I don't get any response from module. I also found out that if I don't specify  data length midlet hangs without error at outstream.write();

Here is working code from PIC microconroller: http://embedded-lab.com/blog/?p=3146

I2C1_Start(); // Issue start signal

I2C1_Wr(TC74A0); // Address + Write bit /TC74A0 = 0x90

I2C1_Wr(0x00); //

Read Temp I2C1_Repeated_Start(); // Issue start signal

I2C1_Wr(TC74A0+1); // Address + Read bit

Here is my code:

String stringData = "0x90";
String readTemp = "0x91";

outStream.write(stringData.getBytes(),0,stringData.length()-1);

System.out.println("instream " + inStream.available());

outStream.write(readTemp.getBytes(),0,readTemp.length());

System.out.println("instream " + inStream.available());

outStream.write(stringData.getBytes(),0,stringData.length());
System.out.println("instream " + inStream.available());

In TC65 example data is shaped like this:

// Write Transfer Frame, where a = message ID, AE = Slave Address and write 
String data = "<aAE000102030405060708090A0B0C0E0F>";

So everything is in one piece. Does anybody know how could I transform my data in just 1 call? Slave adress is : 1001 000
read byte = 1
write byte = 0

Also I checked about SMBus/I2C compatibilty with I2C and there should be no problems.TC74A9 documentation : http://exploringarduino.com/wp-content/uploads/2013/06/TC74-datasheet.pdf

Regards 
Jure
Markus's picture
Markus
Nov 17 2014 - 2:40pm

Hello Jure,

first of all I would check the HW and measure the I2C lines with an oscilloscope.

The BGS5T *****: Vin = 1,3 - 1,85V and Vout has to be set by VCCref

Check that AT^SCFG is configured correctly.

Whe the HW is verified I would dig deeper on SW level.

Regards

Markus

....
I started out with nothing... I still have most of it.

Bartłomiej Gemalto Moderator's picture
Bartłomiej Gema...
Nov 17 2014 - 9:45pm

Hello Jure,

Each message you send must contain the start character "<" and stop character ">".

The second element of each message is the Message ID (1 character). The Message ID serves the user to distinguish

between different messages. It is not sent to the I²C slave device.

So the format of write transfer message should be: < ID SlaveAddress Data >

Maximum length: 2048 bytes for I²C Slave Address and written data.

I can see in your code that you send "0x" - you should remove it. For example send "90" instead of "0x90".

I think you should read about structure of messages on the I²C bus in the AT commands specification. There's also an example. 

You may find there a little bit more than in Java API description. 

Maybe it would be better to test the communication with the AT commands interface first to separate i2c communications problems from Java problems. And when it will work then you can try with Java.

Unfortunately I cannot recommend you any particular sensor.

Best regards,

Bartłomiej

Jure's picture
Jure
Nov 18 2014 - 12:48pm
Thank you. I learned how to structure I2C messages and managed to transfer them trough AT commands. But I am still not quit there.

Protocol is like this:

1.Start condition

2.I send slave adress + write bit

3.Recive ACK

4.Send which register you want to read

5.Recive ACK

6.Start condition

7.Send adress + read bit

8.Recive ACK

9.Revice temperature data

My at commands:
at^sspi=0000,0000,0000

response:connect

<090>  //adress + write bit (1001 000 + 0)
response:0+
<100> //temperature register
response:
1+
<291> //adress + read bit (1001 000 + 1)
{2!0002}

Could be this because I don't send Start condition (a high-to-low transition of
SDA while SCLK is high)? I couldn't find any option for that in the documentation. I tryed to simulate this with stoping connection with '#' and starting it again, but it didn't work.

Regards

Jure

Jure's picture
Jure
Nov 18 2014 - 12:54pm

I also disscoverd that if I enter <080>,<070>... while third byte is zero anything goes trough and I get {0+}.

Bartłomiej Gemalto Moderator's picture
Bartłomiej Gema...
Nov 19 2014 - 8:43pm

Hi Jure,

I don't know the communication protocol with your device but I think that you might have missed one thing - each hex value you send in the i2c frame must consist of 2 characters. So if for example your address is 0x09 and some write request is 0x00, some register 0x33, data you write 0x77 then your frame could look like this: <a09003377>.

You don't drive the lines manually, when you send "<" character the transmission start should be signalled on the interface. If your device meets the i2c standard the signalling should be working. You can only set the data transfer rate while establishing the connection.

Regards,

Bartłomiej

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