In this section, we are going to develop a Contiki-NG application called virtual-sensor. We will use the general library for the sensor, which will be used for temperature and humidity readings. We will create a virtual sensor in a header file that exposes two functions, read_temperature() and read_humidity().

• mysensor.h
• mysensor.c
• demo-sensor.c
• Makefile

$$
Demo-sensor.c
\begin{cases}
&read_temperature()\
&read_humidity()
\end{cases}
$$

• mysensor.h

#ifndef MYSENSOR_H
#define MYSENSOR_H
struct Sensor {
 char name[15];
 float value;
};
struct Sensor read_temperature();
struct Sensor read_humidity();
#endif

• mysensor.c

#include "mysensor.h" 
#include <string.h> 
#include <stdlib.h> 
float random value(float min, float max) 
{ 
 float scale = rand() / (float) RAND MAX; 
 return min + scale * (max - min); 
} 
struct Sensor read temperature() 
{ 
 struct Sensor temp; 
 strncpy(temp.name, "Temperature", 15); 
 temp.value = random_value(o, 35); 
 return temp; 
} 
struct Sensor read humidity() 
{ 
 struct Sensor humdidty; strncpy(humdidty.name, "Humidity", 15);
 humdidty.value = random_value(40, 80); 
 return humdidty; 
} 

• demo-sensor.c

#include "contiki.h" 
#include "mysensor.h"
#include "sys/etimer.h" 
#include <stdio.h> 
PROCESS(sensor_process, "Sensor process"); 
AUTOSTART PROCESSES(&sensor_process); 
static struct etimer timer; 
PROCESS THREAD(sensor_process, ev, data) 
{ 
 PROCESS BEGIN(); 
 printf("Demo Virtual Sensor\n"); 
 while(1) { 
  etimer_set(&timer, 3 * CLOCK_SECOND); 
  PROCESS WAIT EVENT UNTIL(etimer_expired(ftimer)); 
  struct Sensor temp = read_temperature(); 
  printf("%s: %.2f\n", temp.name, temp.value); 
  struct Sensor hum = read humidity(); 
  printf("%s: %.2f\n", hum.name, hum.value); 
  printf("\n"); 
 } 
 PROCESS END(); 
} 

• Makefile

CONTIKI PROJECT = demo-sensor 
all: $(CONTIKI_PROJECT) 
PROJECT SOURCEFILES += mysensor.c 
CONTIKI = /home/user/Documents/book/contiki 
include $(CONTIKI)/Makefile.include 

• Application activation

make TARGET=native
./demo-sensor.native