Sound signaling device for the completion of the work of a household electrical appliance. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power supply

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If a washing machine or other household electrical appliance with a fairly long cycle of operation does not have an audible alarm for its completion, or generates only one short beep pulse at the end of the cycle, which is easy to miss, a simple device can be made and it will give a loud long beep at the right time.

The signaling device is suitable for operation with electrical appliances that consume a power of not more than 2 kW from a single-phase network. A short-term increase in power up to 3 kW is allowed, for example, when turning on the heating element of a washing machine or an electric grill in a microwave oven.

Fig. 1

No intervention in the design of the controlled device is required.

The signaling device circuit is shown in fig. 1. The XP1 plug is connected to the mains, and the device's mains plug is inserted into the XS1 socket. A constant voltage for powering the electronics of the signaling device is obtained using a rectifier on diodes VD5 and VD6 with a ballast capacitor C2. It is stabilized by a zener diode VD7. LED HL1 indicates that the device is connected to the network.

While the appliance is operating, executing a given program, the current it consumes is obviously greater than 0.2 A. The voltage drop created by this current across the resistor R1 opens and closes the germanium transistor VT50 1 times per second, and with it the transistor VT2, the collector current of which charges the capacitor C4. Powerful diodes VD1-VD4 limit the voltage amplitude across the resistor R1 at the maximum load current to approximately 1 V. When the capacitor C4 is charged, the field effect transistor VT3 is open, so the voltage between the control electrode and the cathode of the trinistor VS1 is not enough to open it.

As soon as the appliance, having completed the program, switches to standby mode, the current it consumes will drop sharply, transistors VT1 and VT2 will stop opening. Capacitor C4 will be discharged through resistor R8. After about 3 ... 4 minutes, the voltage between the gate and the source of the transistor VT3 will drop below the threshold at which this transistor closes. Exposure is necessary so that the sound alarm does not turn on when the operating mode of the appliance changes, for example, when the direction of rotation of the washing machine drum changes. As soon as the transistor VT3 closes, the voltage at the control electrode of the trinistor VS1 increases. The trinistor opens through it, the supply voltage is supplied to the generator on transistors VT4 and VT5 [1]. Since this oscillator is excited at the natural resonance frequency of the electromagnetic sound emitter BF1, the signal is very loud.

If the program cycle of the electrical appliance is restarted, the current consumed by it will increase and all processes in the signaling device will go in the reverse order, the sound signal will stop. This will happen due to the fact that the current flowing through the open trinistor VS1 does not exceed 30 mA, and in this mode the MCR100 and some other low-power ones are able to close when the voltage between the control electrode and the cathode drops to almost zero [2]. Such a decrease is provided by the transistor VT3, which opened as a result of charging the capacitor C4. In this device, the trinistor replaces the Schmitt trigger, abruptly turning on and off the power of the sound generator.

Fig. 2

The details of the signaling device are installed on a circuit board with dimensions of 110x65 mm (Fig. 2), their terminals are connected by wires according to the diagram. Those wires through which the current of the controlled electrical device flows are stranded with a large cross section. Their connections are made with tight twists, soldered for greater reliability. The XP1 plug and XS1 socket must be rated for at least 16 A and made of ceramic or heat-resistant plastic. It is undesirable to use cheap electrical fittings made of a beautiful thermoplastic material that easily loses shape at elevated temperatures. To improve the thermal contact of the diodes with the heat sink, a heat-conducting paste is used.

Resistor R1 must be wire, for example, C5-16MB or C5-37. It is not worth using a conventional non-wire resistor (MLT, C2-23) here, since when overloaded, it can fail with a break in the current flow circuit. There are no special requirements for other resistors. Capacitor C2 - film K73-17 or K73-24. Oxide capacitors - K50-35, K53-19, K53-30 or similar imported ones. The remaining capacitors are ceramic K10-17, K10-50.

Diodes KD213A can be replaced by KD213B or more powerful, but much more expensive from the KD2998 series. KD2999. You can replace 1N4006 with diodes 1N4001 - 1N4007 or from the KD105, KD208, KD243 series, and the D814B zener diode - KS191A, KS510A, 1N5346.

Instead of the MP37B transistor, any low-power germanium transistor of the npn structure is suitable, for example, from the MP35-MP38, GT122, 101NU70, GC526 series, and instead of the MPS2907A, 2SC3198 transistors, low-power silicon ones of the corresponding structure can be replaced with any of the ZVN504, BSS2120 or KP88 series, KP501. With all replacements, attention should be paid to the differences in the location of the elements of the same name.

The coil of the electromagnetic sound emitter SBT-1212 has a resistance of about 140 ohms. The emitter can be replaced with another electromagnetic one with a coil of approximately the same resistance, designed for a voltage of 9..12 V. LED - any suitable glow color.

Without connecting the assembled device to a 220 V network, a constant voltage of 10 V is supplied to its capacitor SZ from any source (observing the polarity). The plates of the capacitor C4 are connected by a jumper. The fixed resistor R11 is temporarily replaced with a variable one (with a resistance of 47 ... 68 kOhm) and the position of its engine is found at which the volume of the sound signal is maximum, and when the power is turned off and on again, the generator starts up reliably By measuring the found resistance of the variable resistor, it is replaced by a constant. Further, by removing the jumper from the capacitor C4, by selecting the resistor R8, the necessary delay in the sound signal is set.

Having disconnected the 10 V voltage source from the signaling device, insert the XP1 plug into the mains socket, and into the XS1 socket - the plug of the electric stove, iron or other simple electrical appliance. It is checked that the voltage across the capacitor C4, when this device is turned on, becomes almost equal to the voltage on the zener diode VD7, and after it is turned off, it gradually decreases to zero.

Sometimes the device, the operation of which is to be monitored, consumes too much current in standby mode, and there is no sound signal when switching to this mode. In such a case, it will be necessary to replace the resistor R1 of the signaling device with another one of lower resistance, choosing it in such a way that the signal is reliably turned on and off.

If the VD1-VD4 diodes get too hot, it is necessary to increase the size of the heat sink on which they are installed, or blow the heat sink with air using a fan. For example, a VVF-71M fan operating on a 220 V network, which was used in domestic computers and CNC machines, is suitable. Heating will also decrease when replacing KD213A diodes with Schottky diodes, for example KD2998A. Due to the lower direct voltage drop on such diodes (compared to conventional silicon ones at equal current), the power dissipated by them also becomes less.

Literature

1. Priymak D. Relaxation RL-oscillator: Sat: "To help the radio amateur", vol. 106 - M.: DOSAAF, 1990
2. Butov A. Simple constructions on trinistor KU112A. - Radio, 2004, No. 6. p. 56. 57.

Author: A. Butov, p. Kurba, Yaroslavl region; Publication: radioradar.net

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