In the phones with caller ID is a mode in which the phone operates in the answering machine. In-line standard phrase is pronounced recorded in ROM. For recording telephone messages, you must have an additional sound card, which is due to the relatively high cost is not particularly widespread.
The proposed scheme operates independently of the phone and gives a line phone message, pre-recorded on a cassette recorder.
The circuit consists of an input amplifier transistor VT1, inverters DD1.1, DD1.2, timing chain across the resistor R4 and the capacitor C2, the output of the power amplifier transistor VT3, the load of which is the winding of an electromagnetic relay K1, and the control transistor VT3.
When receiving a call signal relay K1 and their contacts supply power to the recorder, with a linear output which signal is supplied to the transistor VT3 for the transmission line. Simultaneously, the transistor VT3, opening, bypasses the line resistor R8, which is equivalent to lifting the handset on your telephone. Potentiometer R6 is set to this mode of operation of a transistor in which an in-line comes as loud and undistorted signal. The adjustment of this resistor device as is consistent with the coupled lines, and plain. The auto-pick is determined by the value of the resistor R4 and the capacitance of the capacitor C2 is selected equal to the length of time recorded on the tape recorder phrase.
The disadvantage of the scheme is that repeat the same phrase requires rewinding of the tape. To eliminate this disadvantage, it is necessary to tape the same phrase to write down a few times with an interval equal to the time of auto-pick. If you want to not only pass, but also to record a phone message, then the same pair of relay contacts can be used for applying voltage to the second tape recorder in the recording mode In the schema you can use transistors with a static current transfer ratio of at least 100. Diode VD1 - on a direct current of at least 50 mA Relay K1 - RES-9, passport RS4 524 202
Authors: N. Martynyuk, g Kobrin, Brest region; Publication: N. Bolshakov, rf.atnn.ru