If you want to experiment some more here is a very very simple schematic
using no external
power supply. It uses the Parallel port outputpin 2-9 to power it.
It's a little more dangerous for you
parallel port because there is no IC LM324 with external powersource
to protect it. WIth the
other setup if something goes wrong on the PCB board the LM324 will
brack before the parallel
port. Now we are using the parallel port directly to power the LDR's.
This means when you make
an error with this one you could either put or pull to much current
to/from the parallel port and break it.
If you do it right and keep a good eye at the power consumption from
pin 2-9 then it sould be no problem.
Try not to pull more that 2mA per output pin. I tested it out with
the original LDR i use and it workes for me !
Don't forget to still use the externally powered bridge with to high
power red LED's above the sensors.
Here is the drawing :