Home Chipkit Chipkit Uno and GY-21P module

Chipkit Uno and GY-21P module

by shedboy71

The GY-21P is an interesting module in that it combines a BMP280 sensor and an SI7021 sensor. The on-board BMP280+SI7021 sensor measures atmospheric pressure from 30kPa to 110kPa as well as relative humidity and temperature.

Pressure range: 300-1100 hPa (9000 meters above sea level at -500m)
Relative accuracy (at 950 – 1050 hPa at 25 ° C): ± 0.12 hPa, equiv. to ± 1 m
Absolute accuracy (at (950 – 1050 hPa, 0 – +40 ° C): ± 0.12 hPa, equiv. To ± 1 m
Mains voltage: 1.8V – 3.6V
Power consumption: 2.7µA at 1Hz readout rate
Temperature range: -40 to + 85 ° C

Respiratory therapy
White goods
Indoor weather stations
Micro-environments/data centers
Automotive climate control and defogging
Asset and goods tracking
Mobile phones and tablets
Size: 1.3*1cm/0.51*0.39″


Operation Voltage: 3.3V
I2C & SPI Communications Interface
Temp Range: -40C to 85C
Humidity Range: 0 – 100% RH, =-3% from 20-80%
Pressure Range: 30,000Pa to 110,000Pa, relative accuracy of 12Pa, absolute accuracy of 100Pa
Altitude Range: 0 to 30,000 ft (9.2 km), relative accuracy of 3.3 ft (1 m) at sea level, 6.6 (2 m) at 30,000 ft.


I use a variety of Adafruit libraries, took the default examples and made the following out of them





[codesyntax lang=”cpp”]

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BMP280.h>
#include "Adafruit_Si7021.h"

Adafruit_BMP280 bme; // I2C
Adafruit_Si7021 sensor = Adafruit_Si7021();

void setup()
Serial.println("BMP280 and SI7021 (GY-21p) test");

if (!bme.begin())
Serial.println("Could not find a valid BMP280 sensor, check wiring!");
while (1);

if (!sensor.begin())
Serial.println("Did not find Si7021 sensor!");
while (true);

void loop()
Serial.println("BMP280 results");
Serial.print("Temperature = ");
Serial.println(" *C");
Serial.print("Pressure = ");
Serial.println(" Pa");
Serial.print("Approx altitude = ");
Serial.print(bme.readAltitude(1013.25)); // this should be adjusted to your local forcase
Serial.println(" m");

Serial.println("SI7021 results");
Serial.print("Humidity: ");
Serial.println(sensor.readHumidity(), 2);
Serial.print("Temperature: ");
Serial.println(sensor.readTemperature(), 2);





OPen the serial monitor

BMP280 results
Temperature = 27.26 *C
Pressure = 99042.63 Pa
Approx altitude = 191.78 m

SI7021 results
Humidity: 31.04
Temperature: 27.30

BMP280 results
Temperature = 28.43 *C
Pressure = 99044.82 Pa
Approx altitude = 191.60 m

SI7021 results
Humidity: 32.59
Temperature: 28.56

BMP280 results
Temperature = 28.17 *C
Pressure = 99037.41 Pa
Approx altitude = 192.22 m

SI7021 results
Humidity: 32.88
Temperature: 28.46

You can see the temperature output is close between the sensors



Atmospheric Humidity Temperature Sensor Breakout Barometric Pressure BMP280 SI7021 for Arduino


You may also like

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More