A short how to... Led as a Sensor and emiter.. by Seconika

' _______________________________________________________________________
'                                                                        '
' This shows a way to use an ordinary LED as both LED light              '
' and sensor at the same time.                                           '
'                                                                        '
' You can use this to make an LED in to a "Light with touch sensor"      '
'                                                                        '
' This example is reworked from a site with code for ATMEL mcu.          '
' http://www.thebox.myzen.co.uk/Workshop/LED_Sensing.html                '
'                                                                        '
' Feel free to use it if you like it.                                    '
' If you have a better way of doing this, please let me know.            '
' (You find me @ the Crownhill forum, Username: seconika                 '
'                                                                        '
'¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤  HARDWARE ¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤               '
'                                                                        '
' Wire up the LED so that the anode is connected to a digital pin        '
' and the cathode is connected to a an analogue input pin.               '
' Don’t forget a current limiting resistor in each LED.                  '
'                                                                        '
' So, that’s simple enough.                                              '
'                                                                        '
' PORTB.7 ------>|-------|||||------- PORTA.0                            '
'              LED     RESISTOR                                          '
'                                                                        '
' _______________________________________________________________________'


Device = 18F452     ' Select device
Xtal = 20           ' Set speed

    PortB_Pullups = Off     ' Disable Pullup on portB

    ' Set Serial output.
    Hserial_Baud = 38400            ' Set baud rate to 9600
    Hserial_RCSTA = %10010000       ' Enable serial port and continuous receive
    Hserial_TXSTA = %00100100       ' Enable transmit and asynchronous mode
    Hserial_Clear = On                ' Enable Error clearing on received characters
    
    'Set ADC
       Adin_Res    10                    ' Set the resolution to 10
    Adin_Tad    FRC                    ' Choose the RC osc for ADC samples
       Adin_Stime    80                    ' Allow 80us for charge time
       
    DelayMS 100                        ' Wait for PICmicro to stabilise
    TRISA.0 = 1                        ' Setup bit-0 of PortA as an input
       ADCON1 = %10000010                ' Set PORTA analog and right justify result           


Dim Raw1 As Byte           ' get some variables to save data in.
Dim Raw2 As Byte           ' get some variables to save data in.
Dim LightVal As Byte    ' get some variables to save data in.
Dim tByte    As Byte

DelayMS 100

While 1 = 1                 ' Create an endless loop
'1)   Turn LED on.    
    Low PORTA.0             ' Set PORTA.0 To logic zero.
    High PORTB.7            ' Set PORTB.7 To logic one.
    DelayMS 10              ' Now the Led can shine for a while :)
    
'2)   Set LED in measurement mode (Turns the LED off)
    TRISA.0 = 1             ' Set PORTA.0 To ADC input
    Low PORTB.7             ' Set PORTB.7 to logic zero
    
'3-4) Take a measurement of the analogue voltage, this is a reference level for later use.
    Raw1 = ADIn 0            ' Read the ADC

'5)   Wait while the photon current is integrated
'     the longer the more sensitive but too long 
'     and effects other than photo current dominate. 
    DelayMS 8               

'6)    Measure the voltage again and subtract it from 
'      the reference value you took before the integration time. 
'      This value is your light reading
    Raw2 = ADIn 0            ' Read the ADC 

    TRISA.0 = 0             'Low PORTA.0    'Turn LED on again
    High PORTB.7   '
    
    LightVal = Raw2 - Raw1

    If LightVal > 115 Then
       Toggle PORTB.0
       tByte = tByte + 1
    End If
    
    If tByte > 255 Then
       tByte = 0
       Toggle PORTB.0  
    End If    
    
Wend        'Make it all over again :)