Page 362 - ARM Based Microcontroller Projects Using MBED

348 14. ADVANCED PROJECTS

BEGIN/MAIN
Define ESP-01 UART interface
Configure all relays as outputs and de-activate them
Set ESP-01 baud rate to 115200
CALL ConnectToWiFi
DO FOREVER
IF command is ONx THEN
Activate relay x
ELSE IF comman is OFFx THEN
De-activate relayx
ENDIF
ENDDO
END/MAIN

BEGIN/ConnectToWiFi
Send commands to ESP-01 to connect to Wi-Fi
END/ConnectToWiFi
FIG. 14.17 Program PDL.

14.4.7 Program Listing

The program listing (program: esp) is shown in Fig. 14.18. At the beginning of the program
Nucleo-F411RE development board UART1 TX and UART1 RX pins are assigned to esp pins
RX and TX, respectively. Then, the GPIO ports connected to the relays are configured as dig-
ital outputs and all the relays are deactivated. The baud rate of the UART is set to 115200
which is the default value for the ESP-01. Function ConnectToWiFi is called to connect to
the Wi-Fi. The remainder of the program runs in an endless loop formed using a while state-
ment. Inside this loop data is received from the mobile device and the relay is controlled ac-
cordingly. Commands ONx activate relay x. Similarly, commands OFFx deactivates relay x.
Function strstr looks for a substring in a string and returns a nonzero value if the substring is
found. The reason for using the strstr function is because the data received from the mobile
device is in the following format +ID0,n: data (e.g., +ID0,3:ON1) where 0 is the link ID and n
is the number of characters received. Using the strstr function we can easily search for the
strings ONx or OFFx. Notice that logic HIGH deactivates a relay and logic LOW activates it.

AT+RST Reset ESP-01
AT+CWMODE Set ESP-01 mode (here it is set to Station mode)
AT+CWJAP Set Wi-Fi ssid name and password
AT+CPIMUX Set connection mode (here it is set to multiple connection)
AT+CIFSR Returns the IP address (not used here)
AT+CIPSTART Set TCP or UDP connection mode, destination IP address, and port number (here, UDP is used
with port number set to 5000. Destination IP address is set to “0.0.0.0” so that any device can
connect and send data over Port 5000).