Sensor HYT 221 with I2C and 20x2

[woschx]

Hi,

ffor a project I must measure the temperature and the air humidity.
For it I have got myself the HYT 221.

https://www.ist-usadivision.com/objects/media/data-sheets/product/humidity-module/HYT-221.pdf

With an Arduino and this programme I can select the values / register
Code:
#include <Wire.h>
void setup() {
#define HYT_ADDR 0x28 // I2C address of the HYT 221, 271, 371 and most likely the rest of the family
Wire.begin(); // Join I2c Bus as master
pinMode(13, OUTPUT); // Set pin 13 to output for status LED
// I2C Pins on the Arduino Uno are A4 for SDA and A5 for SCL
Serial.begin(9600); // Start serial communication for serial console output
}

void loop() {
double humidity;
double temperature;

Wire.beginTransmission(HYT_ADDR); // Begin transmission with given device on I2C bus
Wire.requestFrom(HYT_ADDR, 4); // Request 4 bytes

// Read the bytes if they are available
// The first two bytes are humidity the last two are temperature
if(Wire.available() == 4) {
int b1 = Wire.read();
int b2 = Wire.read();
int b3 = Wire.read();
int b4 = Wire.read();

Wire.endTransmission(); // End transmission and release I2C bus

// combine humidity bytes and calculate humidity
int rawHumidity = b1 << 8 | b2;
// compound bitwise to get 14 bit measurement first two bits
// are status/stall bit (see intro text)
rawHumidity = (rawHumidity &= 0x3FFF);
humidity = 100.0 / pow(2,14) * rawHumidity;

// combine temperature bytes and calculate temperature
b4 = (b4 >> 2); // Mask away 2 least significant bits see HYT 221 doc
int rawTemperature = b3 << 6 | b4;
temperature = 165.0 / pow(2,14) * rawTemperature - 40;

Serial.print(humidity);
Serial.print("% - Temperature: ");
Serial.println(temperature);
}
else {
Serial.println("Not enough bytes available on wire.");
}
blinkWait();
}

void blinkWait() {
digitalWrite(13, HIGH);
delay(1000);
digitalWrite(13, LOW);
delay(1000);
}

Now I try to select in vain the sensor with 20x2 about I2C and get no reasonable values.
Byte 0 is 29 and the following three bytes 255.
I have pulled SDA and SCL with 4K7 on 5 V. Has developed the opposition also sometimes. It Changing to itself, however, nothing.
SCL on B.7
SDA on B.5

So in the kind I have tested it:
Code:
start:
let b8 = 4
hi2csetup i2cmaster, $28, i2cslow, i2cbyte
; i2cslave $28,i2cfast, i2cbyte
writei2c 0,(b8)
pause 10
readi2c 0,(b0,b1,b2,b3)
debug
goto start

Can somebody help me there?

Wolfgang

 

[AllyCat]

Hi Wolfgang,

Welcome to the forum.

You pbobably need to use Slave address $50 (not $28) as shown in the data sheet page 15, when using a PICaxe. I2C uses the LSB as a Read/Write flag, so the "address" starts at bit 1 (not bit 0).

Cheers, Alan.

 

[woschx]

Many thanks for the info!
Now I get useful register values.
Now by the conversion of the register values in the measuring values I have this here:
------------------------
start:
i2cslave $50,i2cfast, i2cbyte
pause 100
readi2c 0,(b1,b0,b3,b2)
let b1 = b1 and %00111111

let w2 = w0 / 164 ; humidity

let w1 = w1 / 4 ; temperature
let w3 = w1 / 99
let w3 = w3 -40
debug
goto start
------------------------

I have determined the factors 164 and 99, because descendant's calculations are not possible.

Small inaccuracies thereby arise of course in the result!
Is there still a better calculation possibility?

Wolfgang

 

[AllyCat]

Hi Wolfgang,

Yes, if you are entering calibration factors directly into the Progam, the ** operator can be very useful. It multiplies by the subsequent number and then divides by 65536.

So, instead of dividing by 4 and then 99, you can ** 165.4949.... (because 65536 / (99 * 4) = 165.4949..) . That's a rather "unfortunate" number, so in this particular case you might ** 331 / 2 . Thus the calculation could be done as a "one liner" : w3 = w1 ** 331 / 2 - 40 .

But perhaps better to work in tenths of a degree with something like (not tested) :

w3 = w1 ** 1655 - 400
w1 = w3 // 10              ; Remainder = Tenths
w3 = w3 / 10               ; Integer degrees
sertxd("Temperature= ",#w3,".",#w1," degrees C")

Cheers, Alan.

 

[marks]

Hi derschutzhund,
like Allycat has already suggested you can reuse the same variable

also try for temp. w1=w1 *4 **16502 -4000 'ie 6162 =2206 (22.06)
and humidity. w0=w0 ** 4001 ' ie 8045 =491 (49.1%RH)

using the recommended 2.2k pullup should make received data more reliable

 

[woschx]

Thus the ready programme looks!
humidity and temperature are given with two postcomma places.
-----------------------------
start:
i2cslave $50,i2cfast, i2cbyte
pause 100
readi2c 0,(b1,b0,b3,b2)
let b1 = b1 and %00111111

w2 = w0 ** 40001
w0 = w2 // 100
w2 = w2 / 100

w3 = w1 ** 16500 - 4000
w1 = w3 // 100 ; Remainder = Tenths
w3 = w3 / 100 ; Integer degrees

sertxd("Feuchte= ",#w2,".",#w0," %"," Temp.= ",#w3,".",#w1," C",13,10)

goto start
-----------------------------
Many thanks for your help!

Wolfgang