private telephone exchange

7-60 elektor july/august 1980 There are many old telephones around which still look and work fine and which are often put up for sale at a reasonable price. However mundane the use of a telephone is nowadays, secondhand telephones are always fun to have. They are even better of course, if they can be used as a house "phone. The circuit given here shows an exchange for up to nine telephones. They all have a single figure number. However, only one connection between two "phones can be made at any one time. When the receiver is picked up, a continuous tone will be heard. After dialling the number of another phone it is heard to ring. The "bell" inside the phone is operated when its number is dialled from another "phone. lc 2 KI ZV FF2 CL DUS C2 R2 mi 11-1100n Cx Rx/Cx 12V R1 C1. 112V.L I100p 63 private telephone exchange la MMV WI 0 TR 1 a CL IC2 N1 ... N4 = IC1 = 4081 N5 ... N8 = IC3 = 4011 N9 ... N12 = IC6 = 4001 MMV1,MMV2 = IC4 = 4098 FF1,FF2 = IC5 = 4013 80542 2 4017 vcc SND 0 ZA...