Problem Interfacing SMD500 SENSOR UNING I2C

Projects Programming
1

I'm trying to measure pressure and temperature using SMD500 sensor. I used I2C to communicate method, 2 pins interface. The Connection was set as follows:

  • VCC of the SMD500 sensor to 3.3V
  • Connect GND to Ground
    -Connect SCL to i2c clock - on Arduino Uno Analog 5
    -Connect SDA to i2c data - on Arduino Uno Analog 4

The used code for similar sensor is shown below:

#include <Adafruit_BMP085.h>

/*************************************************** 
  This is an example for the BMP085 Barometric Pressure & Temp Sensor

  Designed specifically to work with the Adafruit BMP085 Breakout 
  ----> https://www.adafruit.com/products/391

  These pressure and temperature sensors use I2C to communicate, 2 pins
  are required to interface
  Adafruit invests time and resources providing this open source code, 
  please support Adafruit and open-source hardware by purchasing 
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.  
  BSD license, all text above must be included in any redistribution
 ****************************************************/

// Connect VCC of the BMP085 sensor to 3.3V (NOT 5.0V!)
// Connect GND to Ground
// Connect SCL to i2c clock - on '168/'328 Arduino Uno/Duemilanove/etc thats Analog 5
// Connect SDA to i2c data - on '168/'328 Arduino Uno/Duemilanove/etc thats Analog 4
// EOC is not used, it signifies an end of conversion
// XCLR is a reset pin, also not used here

Adafruit_BMP085 bmp;
  
void setup() {
  Serial.begin(9600);
  if (!bmp.begin(0x77)) {
	Serial.println("Could not find a valid BMP085 sensor, check wiring!");
	while (1) {}
  }
}
  
void loop() {
    Serial.print("Temperature = ");
    Serial.print(bmp.readTemperature());
    Serial.println(" *C");
    
    Serial.print("Pressure = ");
    Serial.print(bmp.readPressure());
    Serial.println(" Pa");
    
    // Calculate altitude assuming 'standard' barometric
    // pressure of 1013.25 millibar = 101325 Pascal
    Serial.print("Altitude = ");
    Serial.print(bmp.readAltitude());
    Serial.println(" meters");

    Serial.print("Pressure at sealevel (calculated) = ");
    Serial.print(bmp.readSealevelPressure());
    Serial.println(" Pa");

  // you can get a more precise measurement of altitude
  // if you know the current sea level pressure which will
  // vary with weather and such. If it is 1015 millibars
  // that is equal to 101500 Pascals.
    Serial.print("Real altitude = ");
    Serial.print(bmp.readAltitude(101500));
    Serial.println(" meters");
    
    Serial.println();
    delay(500);
}

However, the result at the console is illogic:

Temperature = 0.00 *C
Pressure = 235 Pa
Altitude = 30355.89 meters

I looked for solving this problem, I found that the sensor needs master clock input 32768 Hz. However, I don't know how to generate this clock.

Please, help me to solve this problem as soon as possible.

Kindly, find the datasheet for SMD500 sensor.

smd500 datasheet

2

Youll need a clock oscillator. Hopefully with a crystal but the timing spec is loose 3%.
A 555 timer and a few analog parts should be able to run @ 32kHz.
555 calculator

Simple xtal osc:
Crystal-Oscillator

Have you considered a BME280 instead? No external clock needed.

3

Are you sure the I2C pins on the sensor are 5V tolerant?
You could pull them up to 3V3 instead, usually the UNO will still read it correctly, but it's a bit out of the normal operating range.

The 555 is a better option; looks to me the clock pin on that sensor is not a crystal oscillator input, but a lower impedance clock input.
Or just make a clock with the Arduino and a timer.

4

A software timer has too much jitter and millis isn’t fast enough to gen 32kHz, much less 1MHz.

5

One of the hardware timers would do nicely, though.

6

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