Reading an LDR array with a micro

[CyberJacob]

I am trying to repurpose a replica GPO 746 using a micro to replace the phone-line logic, however the rotary mechanism is rather different to that in an original 746.
The circuit has 12 LDRs arranged in an array (3 columns, 4 rows), a shutter attached to the dial, and an LED above the shutter. The shutter is arranged so that when the dial is rotated, a single LDR is illuminated by the LED. The finger stop incorporates a microswitch which powers the LED. I've included a rough circuit diagram below.

The row and column wires were previously connected to an HM9102D, however I cannot reliably replicate the setup using a Raspberry Pi. Reading the GPIO pins via multiplexing seems to have inputs triggered at random, even when the LED is off.

How can I reliably read the inputs from the dial?

[thm_w]

Since this is a switch matrix you need to scan through the rows and columns, you cant just read inputs.

It should work similarly to this:
http://hackyourmind.org/articles/raspberry-pi-with-a-keypad-matrix

Although you may want to check what the open/closed resistance of the LDR is.