Light instead of a call. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Light instead of a call. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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The phone call indicator light can work instead of or simultaneously with a phone call. It will be useful for older people with hearing loss, and will also relieve telephone “trills” at night. The device will be simply necessary if a small child sleeps in the apartment.

Industrial set-top boxes for similar purposes are unreasonably expensive, and the diagram presented in the magazine "Radio" (9/1992) has significant drawbacks: the indicator is activated both during a conversation and when dialing a number, consumes electricity from the network in standby mode, and is inconvenient to connect to the telephone.

The proposed devices are free from all these disadvantages. The article provides three options for implementing such a console. All circuits do not consume energy in standby mode, do not operate when talking or dialing a number on the SLT, and long-term operation of the devices has shown their high reliability.

Light instead of a call
Rice. 2.6. Electrical circuit of the telephone call indicator light

The first circuit (Fig. 2.6) is connected to the telephone line anywhere in parallel with the telephone and does not affect its operation due to the high input resistance. If there is a ringing signal in the line, it is rectified at element VD1 and fed to a reed relay with an operating voltage of 27 V - RES55A RS4.569.601 (RS4.569.606) or RES55B RS4.569.626 (RS4.569.631), which, when triggered, turns on the thyristor VS1.

The circuit can be further simplified if, instead of the VD2 diode bridge, one diode is used, connected to the thyristor in series with the load. Then the brightness of the lamp will decrease and the glow will become slightly pulsating (which is not significant), since it will only operate on one half-cycle of the mains voltage.

All elements of the circuit are placed on a single-sided printed circuit board with dimensions of 67x55 mm (see Fig. 2.7) or can be connected by volumetric installation inside the telephone body. In this case, switch S1 is installed on the housing (see Fig. 2.8), and instead of capacitor C1, a capacitor available in the telephone set in the bell circuit can be used if its capacitance is at least 0,6 μF.

Light instead of a call
Fig. 2.7

Light instead of a call
Rice. 2.8. Option for connecting the light indicator circuit when placing it inside a telephone: HA1 - telephone call; SA1 is a switch associated with the handset position lever.

Capacitors used in the device: C1 - MBM or similar for 160 V; C2 - K50-6 for 50 V. The VD1 diode matrix can be replaced with KTs405B, V, G, D. The use of other types of relays is unacceptable, since they can overload the telephone line when a call signal is active.

If installed correctly, the device does not require configuration. The second circuit (Fig. 2.9) is assembled using a neon lamp (HL1), a transistor self-oscillator (VT1) and a triac switch (VS1).

Light instead of a call
Fig. 2.9

A feature of a neon lamp is its ability to pass current (when it lights up) when the voltage across it exceeds 90 V, which allows it to be used as a threshold element. The call voltage amplitude on the telephone line exceeds this value. Other types can also be used as HL1, for example TN-0,5.

A self-oscillator is assembled on a unijunction transistor, generating short pulses to open a triac switch. If the polarity of the pulse coming to control VS1 is incorrect, the triac will not open (when setting up, you will have to swap the pins on one of the T1 windings).

Light instead of a call
Ris.2.10

Resistor R1 allows you to adjust the sensitivity of the light indicator so that it does not work when dialing a number on your telephone.

The PCB topology for the circuit is shown in Fig. 2.10. The design uses the following parts: capacitor C1 type K52-1B, C2 type K10-17, resistor R1 type SP4-1, the rest - type C2-23-0,5. A triac would be suitable for any other, less powerful one.

The parameters of the pulse transformer T1 are similar to the parameters of the transformer described in the article for the circuit in Fig. 1.17.

The third circuit (Fig. 2.11) is similar in principle to the one described above, but it uses a VD2 zener diode as a threshold element, and in addition to the light, there is a switchable sound indicator.

Light instead of a call
Ris.2.11

The circuit is not critical to parts and does not require configuration if assembled correctly.

When connecting circuits to a 220 V network, it is advisable to observe the phasing shown in the diagram. This will eliminate the possibility of interference entering the TL (at the moment EL1 is turned on) through the isolating pulse transformer T1.

Publication: cxem.net

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