Light Sensor - How to Use Light Sensor

Tutorial Video

Hardware

• PHPoC Blue or PHPoC Black
• Micro USB to USB Cable (to upload source code to PHPoC Device)
• Light Sensor
• Jumper wires

About Light Sensor

Light sensor is used to detect the current ambient light level - i.e. how bright/dark it is. The light sensor used in this example includes three pins:

• VCC pin.
• GND pin.
• Signal pin (outputs analog signal).

How the light sensor works:

• The sensor outputs analog signal to signal pin. There bigger the ambient light level is, the higher the signal value is.

How to use light sensor:

• By reading value of sensor's signal pin, we can infer ambient light level. To read value of sensor's signal pin, we just need to connect the sensor's signal pin to PHPoC device's ADC (Analog to Digital Converter) pin and use PHPoC code to read the value.

We can use another kind of light sensor instead, even if it has different pinout, for example:

• Grove light sensor (for more convenience, use it in combination with PHPoC Grove Expansion Board).
• LDR Photoresistor Light Sensor.

We can use the source code of this example if its working principle is the same as the light sensor used in this example.




Wiring Diagram



Quick Steps

Source code of this example is a part of PHPoC Support Packet (PSP). You need to:

• Download PHPoC Support Package.
• Upload example\p4s\01.php_task\02.adc_light_sensor to PHPoC Blue/Black.
• Click "Run" button on PHPoC Debugger.

If you use PHPoC for the first time, see How To Use PSP.


Source Code

Source files includes:

• init.php: this file is run when PHPoC system is powered or reset. It is used to specify which file is run is system loop.
• task0.php: this file is run in system loop of PHPoC devices.

init.php

This file is run when PHPoC system is powered or reset. It is used to specify that task0.php is run is system loop.

<?php

system("php task0.php");

?>

task0.php

[Full Code]

<?php

if(_SERVER("REQUEST_METHOD"))
 exit; // avoid php execution via http request

include "/lib/sd_340.php";

define("ADC_MAX", 2520);

echo "PHPoC example : P4S-34X / ADC / Catalex Light Sensor\r\n";

adc_setup(0, 0); // adc0, channel 0

$last_adc_in = 0;

while(1)
{
 $adc_in = adc_in(0, 30);

 if($adc_in > ADC_MAX)
  $adc_in = ADC_MAX;

 if(abs($adc_in - $last_adc_in) > 5)
 {
  printf("Illuminance level : %d(%%)\r\n", $adc_in * 100 / ADC_MAX);

  $last_adc_in = $adc_in;

  sleep(1);
 }
}

?>

[Explanation]

Source code of this file does:

• Setup ADC pin.

In infinite loop:

• Read value from light sensor.
• Calculate illuminance level based on the read value.
• Print illuminance level to PHPoC Debugger's console.

See Also

• Light Sensor - Monitoring Light Sensor from Webpage using Hypertext.
• Light Sensor - Monitoring Light Sensor from Webpage with Image.
• Light Sensor - Monitoring Light Sensor via WebSocket.
• Light Sensor - Monitoring Light Sensor via WebSocket with Web-based Gauge.

Other Resources

• PHPoC System Files
• How PHPoC System Works
• How To Use PHPoC Support Package