Picaxe micro-controllers have been used to control everything.
Now that they are easily available at low cost in Canada I made things very modular and I used several of them in the Dalek. The eye stalk, arm and dome all use cheap hobby servos.
I used 3 ultrasonic SRF05 sensors to sense where to look.
I located the Picaxes in different places within the Dalek. Some were located in the neck area and some, which controlled the gun arm and speech, were located in the shoulder area.
A “nervous system” in the neck and shoulders allowed the two sections to communicate with each other.
The SRF05 ultrasonic sensors can detect something (or someone) standing in a zone and will rotate the dome to look at it.
While Talkie Toaster is more interactive and needed a complex conversation, the Dalek did not. The ISD2560 was set to sequential mode.
To make the sound seem more random I used the ultrasonic device to count how long someone was in front of the Dalek and if a person moved away after a given period everything reset to the beginning. In practice people are constantly moving in and out of range so it never just loops in one go.
I used a similar trigger to make the gun move randomly.
The SRF05 ultrasonic detector is very easy to configure and I recommend it.
Schematics for SRF05 ultrasonic detector and code used.