17 ARDUINO PROJECT: Photo Cell

testing a PHOTO CELL
like from here

a nice ADD ON for the RGB / DIMMER project could be a lightsensor
to control the light fixture,
-- as a trigger switch (day / night )
-- or a analog high limitter

a typical photo cell (as a light sensitive resistor )
has about following spec.


wired this cell from 5V -- photo cell -(to Ain 4)- 10K -- GND
i can see following readback voltages:

-- dark -- 0.4V
-- dark by cover with finger -- 1.6V (?? temp / IR sesitive ? )
-- now my ambient room light -- 2.8V
-- focus a LED torch on it -- 4.25V

the cell and resistor is a low price equipment (5THB )

but i am running out of space for screw termination on my board,
and a house installation version of the sensor would be not that cheap
just good to know how it works.

later, in an other article about
LED and LIGHT
i developed a LUX formula
if the photoresistor is in series with a 5kohm resistor as shunt for Ain
and photoresistor on Vcc 5V the calculation could be

LUX = -1 + exp ( 0.00733* Ain )