Phone conversation time counter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Phone conversation time counter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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Recently, in many cities, a time-based system of paying for telephone conversations has been introduced. Most telephones in use today do not have meters. The proposed device will help to estimate the total time of outgoing calls.

The telephone conversations time counter is designed for minute-by-minute recording of the time of outgoing telephone conversations in telephone networks with pulse dialing of the subscriber's number and voltage of 60 V. The conversation time is counted automatically 6 s after the end of dialing the six-digit subscriber's number. After minor alteration, the counter can be used in telephone lines with five or seven digit numbers. The counter does not take into account long-distance calls.

Information about the time of the current conversation and the total time of conversations per month is displayed simultaneously on two scoreboards with maximum readings of 99 minutes and 999 minutes, respectively. The current call time indicator is reset automatically after the handset returns to its original position. The total talk time is reset manually on a monthly basis. To limit the time of conversations, the meter provides an audible alarm every 10 minutes of conversation.

The device is powered by AC 220 V 50 Hz, power consumption - less than 1 W. The emergency power supply of the meter is provided from a 9 V battery of the "Korund", "Krona" types, etc. in case of a power outage. Indications in this mode are not displayed.

The meter has a high input impedance and practically does not affect the operation of the telephone set or line. It can work with any subscriber telephones with rotary or push-button dialers, with cordless telephones.

The scheme of the device is shown in fig. one.

(click to enlarge)

An idea of the operation of the counter is given by oscillograms at some points (Fig. 2).

Call time counter

The voltage divider R1R2 serves as the position sensor of the handset. With a line voltage of 60 V (in standby mode), the voltage across resistor R2 is approximately 10 V, and when the handset is picked up, it is less than 1 V. For the K561LE5 microcircuits used in the meter, this corresponds to high and low levels.

From the output of the voltage divider R1R2, the signal is fed to the input of a waiting multivibrator assembled on elements DD1.3 and DD1.4. Capacitor C1 is used to suppress ringing signals and impulse noise. In standby mode, the output of the standby multivibrator is high. There are no pulses at the outputs of the DD6 chip, since the prohibiting high level from the output of the RS flip-flop DD6, DD3.1 is supplied to the inputs R of the counters DD3.2.

Counters DD7 and DD8 are in a zero state due to the presence of a high level at their inputs S and R coming from the output of element DD2.3. On indicators HG1, HG2, only segments "g" are lit, indicating that the counter is in standby mode.

Counters DD9 - DD11 retain the previously recorded information, since there is a low level at their inputs S. When the SB1 button is pressed, the R20C9 circuit generates a high-level pulse, which puts these counters in the zero state. The indicators HG3 - HG5 are extinguished, since a low level is applied to their grids from the output of the element DD2.4 (through the switch on the transistor VT2).

When the handset is picked up, a low level is set at the input and output of the waiting multivibrator DD1.3, DD1.4. At the outputs of the elements DD2.4 and DD2.3, the levels are reversed. A high level is supplied to the grids of indicators HG3 - HG5 through a transistor switch VT2. Indicators HG3 - HG5 show the information recorded in the counters DD9 - DD11 or zeros if the counters were reset. The inputs S and R of the counters DD7, DD8 receive a low level, and zeros are displayed on the indicators HG1, HG2.

The output of the RS-flip-flop DD3.1, DD3.2 remains high, and the crystal oscillator of the DD6 chip remains in standby mode. The decimal counter DD5, which controls the state of the RS flip-flop, is reset by a high-level pulse generated by the differentiating circuit R12C6 by the voltage drop at the output of the inverter DD2.2. This drop occurs when you pick up the handset.

With the start of dialing, the input of the waiting multivibrator DD1.3, DD1.4 receives a series of from one to 10 pulses each, depending on the dialed digit. The considered version of the device is designed for a six-digit telephone number.

The waiting multivibrator generates rectangular pulses with a duration of 70 ... 75 ms from the dialing pulses received at its input. These pulses come to the transistor key VT1 and buffer inverter DD1.1. The R10C5 circuit suppresses dialing pulses at the input of the Schmitt trigger DD2.4, DD2.3, the output levels of which will depend only on the position of the handset.

The integrating circuit R5C3, together with the transistor switch VT1, forms the envelopes of a series of dialing pulses that are fed to the input of the Schmitt trigger DD3.4, DD3.3. At the output of the element DD3.4, a sequence of pulses occurs, the number of which is equal to the number of digits of the dialed number.

Through the noise suppression circuit R8C4, these pulses are fed to the clock input CN of the decimal counter DD5. When the sixth pulse arrives, a high level appears at output 6 (pin 5) of the counter, which switches the RS flip-flop DD3.1, DD3.2. A low level occurs at the output of the RS flip-flop, which, thanks to the R17C10 circuit, after 6 s allows the counters of the DD6 chip to work. After 1 min at the output M of the counter DD6, a sequence of minute pulses appears, which are fed further to the counters DD8 and DD11.

The minute pulses are counted until the end of the conversation, that is, until the handset returns to its original position. A high level is set at the input and output of the waiting multivibrator DD1.3, DD1.4, and the device returns to standby mode.

When dialing more than six digits at output 7 (pin 6) of the counter DD5, a high level will appear, which will go to the input of the RS-trigger DD3.1, DD3.2 and switch it to its original state. Thus, the time of long-distance calls will not be taken into account.

To give an audible signal every 10 minutes of conversation, output 9 of the match element DD4.3 through the elements DD2.1 and DD4.4 receives pulses from the output P of the counter DD8. Pulses with a repetition rate of 4.3 Hz are received at the other input of the element DD6 from the output F of the counter DD1024. When these pulses coincide in time, an audio frequency signal with a duration of 4.3 s appears at the output of DD0,5. Amplified in power by parallel-connected elements DD4.1 and DD4.2, the signal is fed to the piezoelectric transducer HA1.

The power supply unit of the device contains a parametric voltage regulator based on a VD13 zener diode and an emitter follower based on a VT3 transistor. Diode VD14 prevents the discharge of the emergency battery GB1 in the presence of a mains voltage of 220 V.

The design of the device can be arbitrary. In some telephones, it can be placed inside the case. To improve the visual perception of the meter readings, the indicators should be covered with a green or blue organic glass light filter. It is better to place the SB1 button on the back wall of the case in order to avoid accidental pressing and resetting the counter.

All resistors are MLT. Capacitors C1 - C3, C9, C13 - KM - 6, MBM; C4, C6, C7, C8 - KT - 1, KSO - 1, etc. Oxide capacitors - K50 - 35, K52 - 1, K53 - 1. Microcircuits of the K176 and K561 series can be replaced by similar ones from other series - 564, K1561.

Transistors can be replaced with other silicon ones suitable for current and voltage. Diodes VD1 - VD4 must withstand a reverse voltage of at least 250 V.

Transformer T1 can be any small-sized one with a secondary winding voltage of 12 ... 14 V and a current of up to 100 mA. The filament winding III can be wound with PEL - 1 0,5 wire over the existing windings. The approximate number of turns is 30 - 35.

Indicators IV - 6 can be replaced by IV - FOR. It is allowed to use indicators IV-6 at a heating voltage of 0,85 ... 1,15 V, and IV - ZA - 0,7 ... 1 V. It is undesirable to use ALS LED indicators in conjunction with K176IE4 meters due to the large current consumption and relatively low brightness.

The device does not require special adjustment. After checking the correct installation and operability of the power supply, the meter is connected to the telephone line. By selecting a resistor R2, switching elements DD1.3 and DD1.4 are achieved when the tube is removed. During dialing, the suppression of dialing pulses by the R10C5 circuit is checked and, if necessary, these elements are selected. The delay time for turning on the DD6 crystal oscillator by 6 s can be changed by selecting the parameters of the R17C10 circuit.

It should be borne in mind that the meter readings for the month will still differ slightly from the meter readings of the PBX, since the PBX counts the connection time, and the proposed device - the time interval after 6 seconds from the end of the dialing.

To operate the meter in telephone networks with five- or seven-digit numbers, solder the inputs of the RS-trigger DD3.1, DD3.2 to the corresponding outputs of the counter DD5.

At the beginning of each month, by pressing the SB1 button, you need to reset the counter of the total talk time.

When the telephone line breaks or closes, the counter automatically turns on, time is not recorded.

The emergency battery should be replaced as needed. The battery keeps working capacity more than one year.

Author: N. Shcherbakov, Sevastopol, Ukraine

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