smoke detector

6-32 — elektor june 1980 applikator The MEM 4963, recently introduced by General Instrument Microelectronics, is an IC specifically designed for use in smoke detector circuits, It is an improved version of the older MEM 4962. Many professional smoke detect ion installations use an ionisation chamber and, since this device is radio active, an exclusive permit must first be obtained. In this article we will discuss, what is for us, a more familiar method — infrared light. The drawing in figure 1 illustrates how the presence of smoke can be detected by means of infrared light. An infrared LED and photo diode have been placed at an angle of 45° to each other. Smoke has to be present before the photo diode will detect infrared light. It is really that simple. However, an LED and a photo diode alone do not make for a reliable fire alarm. In figure 2 the complete circuit for a suitable alarm using the MEM 4963 is shown. The circuit can be used as it stands, or, together with any num...