Today in many cities and towns of the country there are timephased payment for telephone calls. Unfortunately, the subscriber discovers spent on the talk time is only sent from the account. To be able to control accounts, offered to produce a counter for the duration of the telephone call from widespread switches Electromechanical hours powered by one galvanic cell, size AA (316, "finger").
The meter circuit is shown in Fig. 1.
In the gap, the phone lines are plot the base-emitter of the transistor VT1, is shunted by the resistor R1, the current flowing in the line when removing the tube, opens the transistor, normally open power circuit Electromechanical hours. They go, counting the time of the conversation. Once handset hung, closed transistor switch interrupts the power supply hours and stops the countdown.
Galvanic element G1, clock supply, conventionally shown in the diagram outside of the housing. However, removing it is not necessary. Rather, as shown in Fig. 2, to insert between a winning output element and a contact spring hours a strip of foil from both sides of the fiberglass thickness of 1 mm or less. To foil layer in contact with the output element, solder the wire that goes the resistor R1 and the emitter of the transistor VT1, to the opposite layer is going to the collector of the transistor.
Resistor - MLT-0.125 or other small-size. Specified in the diagram, the transistor you can replace any low-power silicon structures with p-n-p. the Two parts can be placed in any convenient location, for example, in a telephone wall Jack. Before connect don't forget to check the polarity of the voltage on the telephone line and observe her.
The first day of each month, set the clock to 12:00. By the end of month they will show how much time "talking" on the phone.
The counter duration of the call, mounted on a PBX, only works when the condition that raised the tube phones both parties. The time spent, for example, on dialing and waiting for a response, is not considered. Therefore, the testimony the proposed counter will be high. Unfortunately, to get rid of this lack of simple means impossible.
Author: N. Sakevich, Krasnoyarsk