Interface with Sensirion EKH5 with Sensor SHT2x

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andreu
Posts: 4
Joined: Thu Feb 27, 2014 5:44 pm

Interface with Sensirion EKH5 with Sensor SHT2x

Post by andreu »

Hi guys,

I am communicating with the Sensirion EKH5 with Sensor SHT2x but I don't know what values I have to write in order to get the proper values of temperature and humidity from the sensor.

These values from a SHT75 that I found in this forum:

//Init I2C mode
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0x00;

//Init SHT75 measurement
report[0] = 0x02;
report[1] = 0xC2;
report[2] = 0x50;

//Report Data
report[0] = 0x03;
report[1] = 0x03;
report[1] = 0x03;

Does anybody know what values are the correct ones for the sensor SHT2x?
Also, if I get the correct values what is the correct formula for the calculation of the Temperature and humidity?

Thanks a lot for your help! I appreciate.

Regards,

Andreu

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Christoph Jung
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Location: Germany / Berlin
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Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by Christoph Jung »

Have you take a look into the datasheet about the SHT2x sensor?
On page 7-9 shows the values to send and read from the device.

I have no SHT2x and can't test or send you sample code, sorry.

Untested sample:
The default address if the i2c should be 0x80 for write and 0x81 for read.
to start a measurement the command is 0xE3 for "Temperature", 0xE5 for "Humidity", and "Softreset" 0xFE.

The basic transaction:

Code: Select all

report.ID = 0x02;
report.Bytes[0] = 0xC2;
report.Bytes[1] = 0x80;
report.Bytes[2] = 0xE5; //humidity

IowKitWrite()....
IowKitRead()... //ACK

report.ID = 0x03;
report.Bytes[0] = 0x03;
report.Bytes[1] = 0x81;

IowKitWrite()....
IowKitRead()... // Measurement MSB, LSB and Checksum

double value = (double)((report[2] << 8) | report[3]);

The formula for the SHT7x sensor to get the °C and %RH:

Code: Select all

        //Calc temperature and humidity 
        public void CalcTRH(double temp, double humi)
        {
            const double C1 = -4.0;         // for 12 Bit
            const double C2 = +0.0405;      // for 12 Bit
            const double C3 = -0.0000028;   // for 12 Bit
            const double T1 = +0.01;        // for 14 Bit @ 5V
            const double T2 = +0.00008;     // for 14 Bit @ 5V

            double rh = humi;				// rh:      Humidity [Ticks] 12 Bit 
            double t = temp;			    // t:       Temperature [Ticks] 14 Bit
            double rh_lin;					// rh_lin:  Humidity linear
            double rh_true;					// rh_true: Temperature compensated humidity
            double t_C;						// t_C   :  Temperature [°C]

            t_C = t * 0.01 - 40;						        //calc. temperature from ticks to [°C]
            rh_lin = C3 * rh * rh + C2 * rh + C1;		    	//calc. humidity from ticks to [%RH]
            rh_true = (t_C - 25) * (T1 + T2 * rh) + rh_lin;	    //calc. temperature compensated humidity [%RH]

            if (rh_true > 100) rh_true = 100;		//cut if the value is outside of
            if (rh_true < 0.1) rh_true = 0.1;		//the physical possible range

            m_Humidity = rh_true;   //return humidity[%RH] into member-var
            m_Temperature = t_C;      //return temperature [°C] into member-var
        }
Maybe the formula will work for the SHT2x
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andreu
Posts: 4
Joined: Thu Feb 27, 2014 5:44 pm

Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by andreu »

Hi,

yes I took a look at the data sheet. The problem is that writing address 0x80 (128), the iowkit write function gives back 0 bytes written...

this is what I do:

//Soft reset
report[0] = 0x80; //I2c address + write
report[1] = 0xFE; // Soft reset
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

the value returned is ret= 0.

On the other hand, if I write:
//Soft reset
report[0] = 0x01;
report[1] = 0xFE;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

the value returned is ret=8. That means that the bytes were written on the USB, right?
What I do not understand is why 0x01!! It should be 0x80 according to the datasheet.

Trying to read temperature I also have the problem:

report[0] = 0x80; //I2c address + write
report[1] = 0xE3; // T measurement HM
report[2] = 0x81; // I2c address + read
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

the value returned is ret= 0 again!
obviously I can't even send a read:
ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);
because it won't read any data

report is an array of bytes[8]

Anybody knows where the problem could be?

Thanks!

Andreu

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Christoph Jung
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Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by Christoph Jung »

You have forgotten the report.ID, the flags and the number of data.
And you have to initiate the I2C-Mode once

Init I2C:

Code: Select all

report[0] = 0x01;
report[1] = 0x01; //enable
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
Write:

Code: Select all

report[0] = 0x02; //I2C write mode
report[1] = 0xC2; //startbit, stopbit and 2 data to send
report[2] = 0x80; //I2C device address (from datasheet)
report[3] = 0xFE; //command
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
IOWarrior.Functions.IowKitRead(Handle, 1, report, 8); //swallow the ACK message and free the buffer
Read:

Code: Select all

report[0] = 0x03; //I2C read mode
report[1] = 0x03; //3 Bytes to read
report[2] = 0x81; //Address 0x80 + 0x01
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8); //write to the IO-Warrior, that we will read 3 Bytes of data

IOWarrior.Functions.IowKitRead(Handle, 1, report, 8); //read the 3 Bytes
For read from the I2C you have to set the device address to read-mode -> 0x80 + 0x01
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andreu
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Joined: Thu Feb 27, 2014 5:44 pm

Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by andreu »

Hi,

thanks I tried that, but I always get following result back:
1st read:
report[0] = 2
report[1] = 128
2nd read:
report[0] = 3
report[1] = 128
and so on... (being the rest of the values 0).

which does not seem to me any temperature reading...
I have also tried to add the Read Temperature command HM (0xE3) in report[3] in the write function and I get the same result as above...

According to the commands of SHT25 datasheet I would only need to do following:
"Read Temperature with hold master":

I2C address + write: 0x80; --> in report[0]?
Command: 0xE3; (read temp) --> in report[1]?
I2C address + read: 0x81; --> in report[2]?
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
Thread.Sleep(100);
ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

but I only get always as a result:
report[0] = 2;
report[1] = 128;

This makes me think that maybe there is something wrong with the iowkit.dll and their functions? maybe not the right version?
Since I am using the EKH5 evaluation sensor (USB dongle), I am not sure if I have to do anything else or send any other commando to get it work...

I did not find any I2C write mode (0x02) and read mode (0x03) in the datasheet of SHT25. Do they belong to another sensor maybe?

Thanks for your support!

andreu

andreu
Posts: 4
Joined: Thu Feb 27, 2014 5:44 pm

Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by andreu »

Hi there,

I already found where the problem was. Now I get the temperature without problem.
At the end of the SHT2x datasheet it states that you can use the same protocol as in SHT7 so I did that based on this entry:

viewtopic.php?f=1&t=1694

//sensor first time setup
//I2C enable, pull up disabled
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0xC1;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0xC1;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

//Read status register
report[0] = 0x03;
report[1] = 0x02;
report[2] = 0x07;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

//Setup to get temperature and humidity
//Read status register
report[0] = 0x03;
report[1] = 0x02;
report[2] = 0x07;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

//Generate start, data count=1 byte
report[0] = 0x02;
report[1] = 0x82;
report[2] = 0x06;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

//Inside the loop to read temp
//Measure temperature, read off 3 bytes
report[0] = 0x03;
report[1] = 0x03;
report[2] = 0x03;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

The formula to calculate temperature for SHT2x is:
First get value from 3 bytes:
value = report[2] * 255 + report[3] + report[4] / 255;
temp = value/2^14 * 175.72 - 46.85;

Now works perfect.

Thanks for your support!

Andreu

UKrieger
Posts: 3
Joined: Wed Jan 14, 2015 5:43 pm

Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by UKrieger »

Hi Andreu,

I am trying to use your example to access the SHT25 using Agilent VEE. The equivalent of your example code runs fine up to the point marked below:

//sensor first time setup
//I2C enable, pull up disabled
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0xC1;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0xC1;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

//Read status register
report[0] = 0x03;
report[1] = 0x02;
report[2] = 0x07;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

Up to here everything is as expected the return value of ret is 8 as I expect it. But now:

ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

Here the value of ret is 0 and it should be 8, correct?

Any Idea whichcould cause the read not to work?

Thanks,

Uli

UKrieger
Posts: 3
Joined: Wed Jan 14, 2015 5:43 pm

Re: Interface with Sensirion EKH5 with Sensor SHT2x

Post by UKrieger »

Hi everybody,

I solved the problem, for those interested I could pass the VEE code.

Uli


UKrieger wrote:Hi Andreu,

I am trying to use your example to access the SHT25 using Agilent VEE. The equivalent of your example code runs fine up to the point marked below:

//sensor first time setup
//I2C enable, pull up disabled
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0xC1;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);
report[0] = 0x01;
report[1] = 0x01;
report[2] = 0xC1;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

//Read status register
report[0] = 0x03;
report[1] = 0x02;
report[2] = 0x07;
ret = IOWarrior.Functions.IowKitWrite(Handle, 1, report, 8);

Up to here everything is as expected the return value of ret is 8 as I expect it. But now:

ret = IOWarrior.Functions.IowKitRead(Handle, 1, report, 8);

Here the value of ret is 0 and it should be 8, correct?

Any Idea whichcould cause the read not to work?

Thanks,

Uli

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