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355

One Wire (OW) – Interfacing DHT22 Hygrometer Sensor

Like DS18B20, DHT22 (a.k.a AM2302) digital relative humidity-temperature or hygrometer sensor uses

time-slotting principle over one wire to transfer data to its host controller. Apart from other technical

specs, these sensors differ in terms of time-slots and in the process of data exchanging and

communication bus arbitration. Since data is transferred digitally over one wire, there is no need for

such sensors to be present on board and close to the host MCU. Thus, such sensors can be placed

significantly far from the host micro. This is not so easily possible with analog sensors or with sensors

using multiple wires. This feature is what makes OW communication method an impressive one.

Code Example

DHT22.h

#include <msp430.h>

#include <delay.h>

#define DHT22_DIR P2DIR

#define DHT22_OUT_PORT P2OUT

#define DHT22_IN_PORT P2IN

#define DHT22_PIN BIT0

#define DHT22_DIR_OUT() do{DHT22_DIR |= DHT22_PIN;}while(0)

#define DHT22_DIR_IN() do{DHT22_DIR &= ~DHT22_PIN;}while(0)

#define DHT22_IN() (DHT22_IN_PORT & DHT22_PIN)

#define DHT22_OUT_LOW() do{DHT22_OUT_PORT &= ~DHT22_PIN;}while(0)

#define DHT22_OUT_HIGH() do{DHT22_OUT_PORT |= DHT22_PIN;}while(0)

#define TRUE 1

#define FALSE 0

extern unsigned char values[5];

void DHT22_init(void);

unsigned char DHT22_get_byte(void);

unsigned char DHT22_get_data(void);

Texas Instruments MSP430 User Manual

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