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Dual synchronous telephone toll totalizer circuit

2016-02-07 02:45  
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Totalizers are the simplest and most common type of counter, used in a variety of applications where accurate totals are needed.The Telephone loll Totalize -built around two4518   dual synchronous up counters, a 74C925 4-digit counter, a 4 584 hex inverting buffer, and a 4081 quad 2-input AND gate is fairly simple. Approximate toll charges can be calculated with this counter. It is started when dialing and stopped (manually) on hang-up. It is actually a counter that measures the time you are on the telephone. By calibrating it to the average cost/second of calls (get this from calculations you have done on your monthly phone bill), you can closely estimate your phone bill. The circuit consists of an oscillator running at the 100 000 frequency into the main counter (74C925  ). Typically, cost of telephone calls is 15 to 25 cents/minute so that the clock frequency (Ul) is in the 25- to 40-kHz range. U2 and U4 with gates U3 form a ~ 100000 counter. The approximate cost in dollars and cents is read out on the multiplexed display, DISP 1, 2, 3. S2 resets the counter to zero after each use.The totalizer then causes the coin signal oscillator to readout a dual-frequency signal indicating the value deposited to ACTS (a computer) or the TSPS operator.  These are the same tones used by phreaks in the infamous red boxes.


Telephone Toll Totalizer