Electronic bell-pull

821electronic bell-pull The simplest circuit in this issue of Elektor Electronics consists of a single transistor and resistor, which, when put together as shown, con- stitute the electronic equivalent of an old fashioned, stylish bell-pull used in conjunction with a chime or bell circuit of any relative complexity of- fering whirling melodies, buzzing or ringing sounds, or chime imitations to prompt the houseowner to open the front door. The bell-pull is made from a TO39-style NPN transistor which is taped or isolated by means of a length of heat shrink sleeving, after the emitter and collector leads have been fitted with wires for the elec- trical connection to the bell circuit. A small, conductive plate is secured onto the isolated transistor head, and the base lead is joined to this plate over a series resistor which is dimen- sioned according to R= Ub/5 [162]. The completed assembly may also 12 Ub R - (kri) 5 be cast into epoxy resin to make a nice compact unit that can han...