Matt circuit

This circuit is intended as a replacement for the electronics in a partly or wholly defective autofocus driver in a slide projector. The mechanical parts in the autofocus system are assumed to be still functional. Auto Focus for Slide Projector Fig. 1 :     Most automatic focusing systems in slide projectors  are based on the use of an optical module, which comprises a small lamp, a few lenses and mirrors, and a light sensor made from two series connected light dependent resistors (LDRs), which function as a potential divider. As shown in Fig. 1, lamp La projects a narrow beam onto the centre of the slide, A, whose surface reflects it onto the LDRs. When the slide surface bulges inside or outside, the projected image on the screen is blurred, and the beam from L is received on the surface of one of the LDRs (point 2 or 3). This is detected by a motor driver circuit, which ensures that the focal distance between the objective, 0, and the slide surface is corrected to maintain a sharp...