12F629 LDR - Light Dependant Resistor

[Dennis]

Hi all

I've been dabbling with an LDR and a PIC 12F629 (any PIC should work though) and found it so straight forward and simple that I thought some forum users might enjoy it and come up with some more interesting ideass.
This really does add a whole new dimension to the traditional day/night sensor. You could start logging the amount of actual daylight etc.

LDR's can be setup using either one of two very simple circuits.See this link for more info, I found it very helpful and interesting.
http://www.doctronics.co.uk/ldr_sensors.htm

Here is the code

*************************************************************************************
'12f629 to demo the use of an LDR by DENNIS
'see ldr test scehmatic
'USES ONLY 1 PIC PIN
'                +---+--+---+
'            VCC 1   +--+   8 GND
'    OSC1,X1,GP5 2          7 GP0,CIN+,PGD
'    OSC2,X1,GP5 3          6 GP1,CIN-,PGC
'  VPP,/MCLR,GP3 4          5 GP2,T0CKI,INT,COUT
'                +----------+
'                12Cxxx, 12Fxxx
'
' I tested circuit in daylight and indoors, make sure you have enough light and dark separation
' Adjust the 10K potentiometer for the correct sensitivty
' For reverse operation just change IF GPIO.2 = 1 then dark << replace with 0
' This circuit does not require any crucuial timing and can be moved to any PIC 
'************************************************************************************

        define OSC 4 '4MHz
        DEFINE OSCCAL_1K 1          ' Set OSCCAL for 1k -HELPS tuning the crystal for more accurate timing
        CMCON = 7                    'set digital mode
        'ansel = 0                   'GPIO.2 and GPIO.3 set as digital - disable if using 12629 for LDR
       'TRISIO = %76543210          ' port GPIO 0=output and 1=input
        TRISIO = %0000100          ' GPIO.2 is an input - all the rest are outputs
        
        
' Variables 
LED var GPIO.0
' end of variables
        Start:
            If GPIO.2 = 1 then night
            HIGH led  'Turn on/off whatever you like by changing this line/replacing LED
            goto start 
        
        Night:
            Low led     'Turn off LED (or device)
            
            goto start
            END

In my experiment I found the best light source to be real daylight, and walking around with the breadboard as I walked in and out the door the LED would switch off (in the dark- indoors) or on (outside in daylight).
To alter the sensitivity the 10K pot can be adjusted, I found that halfway worked well.
You can reverse the operation , in other words, off at night and on during the day by just changing the 1 in this line to a 0

If GPIO.2 = 1 then night

The schematic is attached.

Hope this helps someone, and post back any info about how it worked for you or what could be changed or added :-)

Kind regards

Dennis

[mtripoli]

You don't really mean "-5V" in the schematic... call it "ground" or something... else we see the little gears in the IC come flying out...

Mike Tripoli

[Dennis]

Hehehe
Speed kills hey ?
Well that would make 10V the supply then :-) and without a regulator mmm could prove interesting ;-)

Mike ..thanks a million for catching that one in time :-)
Yes it definitely must be GND not -5v as in the schematic :-)
Will see if I can replace the schematic :-0

Keep well

Kind regards
Dennis

[Dennis]

Here it is .. the schematic corrected to show +5V and GND rails :-)

Kind regards
Dennis

[BobK]

Hi Dennis,

So you have an LDR and a pot and a 1 k resistor across the supply rails. Isn't this combination suppose to connect to an input on the micro? I mean how else is the micro suppose to sense a change then turn the LED on?
Just an observation!

BobK

Nice program example though!

[Bruce]

Wiper on POT to GPIO.2..?