It's a sad fact that you often don't appreciate something until you no longer have it!

This was driven home recently to the author when he acquired a "new" car. The first dark evening he jumped in and shut the door, and was plunged into total darkness. The mere 12-second delay fitted to the previous vehicle was ample to settle in and drive away. It was then decided that some form of interior lamp delay was a must.

There have been plenty of past articles showing potentially usable circuits based around chips such as the ubiquitous 555. Whilst perfectly functional, these circuits are limited in additional features. In this design, full advantage is made of a PIC16x84 to provide features that would have required a large amount of logic not so long ago.

This enhanced PIC16x84 circuit not only provides the usual car interior light (dome light) delay but also includes a battery saver function, extinguishing the light if a door is left open for more than 5 minutes. It also has a "lights-on" warning triggered when the lights are on, ignition off and a door is opened. Simple to build, versatile design.