With the DHT11 library, the humidity and temperature sensor DHT11 can be read out via one wire and a microcontroller of the MSP430 series. As microcontroller is used the MSP430G2553 (on the EXP430G2 launchpad) and as a development environment is used the IAR Embedded Workbench.
Download DHT11 library
dht11-library.zip
Schematic EXP430G2 and DHT11
The circuit is quite simple. The DHT11 can tolerate voltages of 3 up to 5.5 V, but since the MSP430 can handle 3.3 V, both ICs are operated with 3.3 V. In addition, a 4.7 kΩ pull-up is required. The complete circuit can be seen in the following figure.
Description DHT11 library
| void DHT11_init (void) |
| Initialization of DHT11, the MSP430 Timer A and GPIO-Pin 1.4 are initialized |
| int DHT11_read (unsigned char *p) | |
| Reads a complete packet (humidity, temperature, and CRC checksum) from the DHT11. | |
| *p | Array contains the information for temperature and humidity. The array has the following format:
P [0] = start bit P [1] = humidity of the DHT11 P [2] = humidity (decimal place) of the DHT11 P [3] = temperature of the DHT11 P [4] = temperature (decimal place) of the DHT11 P [5] = CRC check sum of the DHT11 |
| return | Returns the status of the DHT.
-1: Transmission is faulty 0: Transmission correct -4: No start bit |