Voice relay. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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I propose a simple acoustic machine for turning on various actuators. The essence of the scheme (Fig. 1) is as follows. At a certain level of acoustic noise near the highly sensitive sensor-microphone BM1, the threshold level of which is set by the tuning resistor R1, the signal amplified by the operational amplifier DA1 is fed to the transistor switch VT1-VT2, which supplies power to the relay K1. The relay with its contacts (they are not shown in the diagram) closes the load supply circuit. After the noise stops, the load is turned off.
Fig.1. Schematic diagram of an acoustic machine
This method is used in micro voice recorders, which automatically turn on the recording mode when there is a sound signal. I use this circuit to automatically turn on the UZCH intercom.
This scheme will serve well in the automatic lighting. Then it should be supplemented with a final stage with a turn-off delay of 3...4 minutes. If you install such an automatic machine, for example, in the hallway, then the light will turn on automatically if there is the slightest noise (an opening door or a voice) and go out after a few minutes with complete silence.
In the initial state, both inputs of the DA1 microcircuit are in a state of equilibrium, and a very weak signal, on the order of several millivolts, is supplied to the base of the transistor VT1, which is insufficient to open the transistor. When sound impact on the microphone, an alternating voltage is applied to the input 2 of the op-amp. The multiply amplified signal from terminal 6 of the OU, still amplified by the transistor VT1, enters the electronic key on the transistor VT2, which, in turn, switches the actuator - relay K1.
From the ratings of C5 and R2 depends on the delay of turning off the relay when the sound effect on the microphone disappears. If the delay is not needed, these elements are excluded from the circuit. When a longer turn-off delay is needed, the value of C5 should be increased. With the ratings indicated on the diagram, the turn-off delay when the circuit is powered by 12 V will be 1 min ± 10%. If the capacitance of the capacitor C5 is increased to 2000 uF, the turn-off delay at the same supply voltage will increase to 10 minutes. However, in the latter case, the accuracy of the exposure time is lost and the dependence on the duration of the initial impact of sound vibrations on the microphone increases.
Diode VD1 is used to eliminate the bounce of the contacts of the relay K1. K1 - a low-power relay of the RES10, RES15 type for an operating voltage of 9 ... 11 V. To switch powerful load circuits with a high supply voltage, it is necessary to observe safety measures and use a relay with the appropriate allowable current through the contacts. The BM1 microphone is a DEMSh capsule or similar with a winding resistance of 200 ... 250 ohms and higher. Good results are obtained when using an MCE electret capsule of various modifications as a microphone (previously used as a built-in microphone in cassette recorders).
To eliminate interference and other interference, the microphone must be connected to the device with a short shielded cable no longer than 20 cm. various impacts (for example, slamming the next door) did not affect the microphone.
As VT2, you can use medium power silicon transistors KT603, KT630 or their analogues with any letter indices. As a VT1, KT361 with any letter index is suitable.
Properly assembled from serviceable parts, the device practically does not need to be configured. It is only necessary to select the threshold of operation of the device with a trimming resistor R1.
Author: A.Kashkarov, St. Petersburg; Publication: cxem.net
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