Call counter

A1 ,A2 = IC1 = LM393 51 on/off 9V IC1 IC2 IC3 00 A telephone has the unfortunate dis- 2 advantage that you have to be near it to be able to make use of its com- munication possibilities. If you have a telephone answering unit, you know at least who has called and how many callers there were. If you cannot, or do not want to, hire or buy such a unit, the present low-budget one may be of interest. Low-budget involves the limitation, however, that the in- coming calls are merely counted: who has called, or what the message was, can only be guessed. Moreover, to avoid problems with British Telecom (or whoever your PTT auth- ority is), the unit is acoustically coupled to the telephone. Such a design must, of course, have ex- cellent pulse suppression, since ex- traneous sounds must not be inter- preted as an incoming call. Finally, the counter"s current consumption "see text R C3 S3 I S2 12 B 12 a 65 EE July/August 1986 call counter 421 9V C1 4p7 16V 47n O 11E1 j RESET 1 111 DISPLAY R8...