sensibell

7-04 elektor july/august 1980 r - • see text L R3 R12 15V 811 P2 0 _15V R2 Remember the old-fashioned copper bell-on-a-chain? In many ways it had considerable advantages over its modern electronic counterparts, advantages which were probably not appreciated at the time. It happened to provide a lot of useful information about the visitor. The way in which he rang — loud, soft, long, short, repeatedly, persistently, etc. said a great deal about him. All this of course is lost with the splendid elec- tronic versions of today. There are two ways of salvaging the old type of doorbell. First, you can hunt around until you find one in a second-hand shop. After all, they use very little electricity. Second, the electronic way, which is to build a "Sensibel I". The important component involved is a piezo element, from an ultrasonic transducer. When a voltage is connec- ted to it it becomes distorted, when distorted it produces a voltage. If we use the element as a bellpush, two voltag...