Acoustic Sensor

Using the described construction, it is possible to determine whether or not a mechanism located in another room or building works. Information about the work is the vibration of the mechanism itself. The design is quite simple and contains a minimum of details.

In automation systems it is often necessary to determine the state of a device or mechanism simply at the “on - off” or “working - not working” level. A fairly real and vivid example is a mini-boiler pump.

The boiler itself with a control device (controller) can be located in one room, and a pump that creates pressure in the heating system in another. And not even just in different rooms, but in general in neighboring buildings.

How to inform the controller that the pump is turned on and running? Of course, in simpler systems, not a controller can be used, but a simple and cheap signaling device to attract the operator's attention.

There are several ways to find it. For example, using an additional contact of the starter that turns on the pump: the contact is closed, therefore, the pump is working. Although, for some reason, it may not work. In addition, the starter does not always have an idle contact. This is another drawback of such a scheme.

In addition to this method, you can get a signal about the pump by using a current sensor. Such a signal will more objectively reflect the operation of the device as a whole than the aforementioned contact. The disadvantage of this method is the interference in the drive circuit.

How to control the installation without interfering with its circuit? It turns out quite simply if we recall that the pump mentioned during operation creates noise and vibration. Many other devices possess the same properties: electromagnets, powerful transformers, just mechanical parts of an electric drive. The operation of the mechanism operation sensor described below is based on these “harmful” properties. Similar sensors can also monitor the status of a device equipped with an internal combustion engine or diesel engine.

In the operation of the sensor, vibration is used to a greater extent than noise, therefore, when installing it, you should find the place of the mechanism where the vibration is sufficient to trigger the sensor. At the same time, an elevated temperature is not desirable at the installation site of the sensor. Schematic diagram of the sensor is shown in Figure 1.

Figure 1. Scheme of the sensor of the mechanism (to enlarge the scheme, click on the picture).

The circuit is quite simple and contains only 3 transistors. The principle of its operation is very similar to the operation of the hitchhiking circuit in tape recorders: while pulses are being sent from the magnetic tape motion sensor, a stop signal is not generated. The tape is jammed or has run out - the mechanism has stopped.

In our case, the vibration sensor is an electret microphone M1, the signal from which is fed through a capacitor C2 to an amplifier made on a transistor VT1. Through the capacitor C3, the variable component of the amplified signal is supplied to the rectifier, made according to the voltage doubler circuit. The rectified voltage charges the capacitor C4, so the transistor VT2 will be open (low voltage on the collector). This low level keeps the transistor VT3 closed, so relay P1 is turned off and there is no alarm signal to the controller or signaling device. The emitter of the transistor VT3 installed diode VD4. This is the so-called level lock, which provides a more reliable closing of the transistor.

If the mechanism stops, the vibrations cease, and the microphone simply has nothing to catch. Therefore, the pulses on the collector of the transistor VT1 cease, and the capacitor C4 is discharged.Therefore, the transistor VT2 closes, and VT3 opens and turns on the relay P1, the contacts that inform the controller about the emergency.

Device setup

Setting up the device is easy. First of all, using a resistor R2 on the collector of transistor VT1, you should set the voltage to about half the supply voltage. In this case, the transistor VT1 will operate in linear mode, i.e. as a signal booster.

The second tuning step is to set the sensitivity level of the entire sensor as a whole using a variable resistor R4. To do this, translate its engine to the lower position according to the scheme. This is the minimum sensitivity of the sensor, in this case the relay will be turned on. Then, having placed the microphone in the place where it will be installed, by turning the tuning resistor R4, turn off the relay. When the mechanism is turned off, the relay should turn on again.

Parts and construction

If it is planned to manufacture several instances of the sensor, it is best to assemble the circuit on a printed circuit board. It is most simple to make it by laser - ironing technology. If only one copy is required, then it is quite acceptable to assemble it with a hinged installation. The assembled board should be placed in a plastic case with fasteners.

Transistors VT1, VT2 can be replaced by KT3102 with any letter index, KT503 by KT815 or KT972. All diodes can be replaced by any high-frequency low-power, for example, KD521, KD503.

All resistors type MLT-0.25 or imported. Electrolytic capacitors are also easier to buy imported at a working voltage of at least 25V.

As a relay P1, it is permissible to use any small-sized relay, possibly also an imported one, with a tripping voltage of 12V. The device can be powered from a low-power source, for example from a Chinese network adapter.

If you make the power supply yourself, you will need a transformer with a power of no more than 5 W, with a secondary winding voltage of about 15 V. It is easiest to assemble such a source on the basis of the integral stabilizer 7812. Such a circuit is quite easy to find, so its description is not given here.

Boris Aladyshkin