SOS - a signaling device of disconnection from a network

Unexpected shutdowns of mains voltage became one more (in addition to two known) the Russian trouble. The main thing in such situation - in time to learn about shutdown and to take measures - to pass to a reserve food (if there is a possibility) or it is simple to clean perishable goods from the idle refrigerator. It is easy for making in the evening when about lack of tension the gone-out lamps signal. In the afternoon or late night no obvious signs of shutdown are present and he can be not noticed in due time. The device described in article gives a sound signal lasting more than a minute in some seconds after tension loss in a network.

---

the Offered signaling device (its circuit is shown on fig. 1) is constructed by p by the same principle, as A.Dolgogo described in article "A sentry dog for the computer" ("Radio", 2000, No. 2, page 27).

of the Fig. 1. The schematic diagram of a signaling device

Mains voltage arrives on two rectifiers. On an exit of first (VD1C1) - tension of the positive polarity, second (VD2C2) - negative. Face values of R2 and R3 resistors are chosen in such a manner that the field VT1 transistor is closed, the chain of a call of an electromechanical alarm clock is broken off. At loss of mains voltage condensers C1 and С2 start to be discharged. But as their capacity is various, the discharge occurs to unequal speed. Tension of negative polarity (fig. 2, a curve 1) falls down quicker, than positive (a curve 2) therefore tension on a VT1 transistor lock (the curve 3) quickly grows. As soon as it (at the moment of t1) will exceed threshold value (Uп), the VT1 transistor will open and will close a call chain.

of the Fig. 2. Temporary charts

Thanks to VD4 stabilitron tension on a lock of the transistor is limited to safe values for the last 0 and Uст (without a stabilitron it could reach 100 In and more, as shown the shaped line). At the moment of t2 when the C1 condenser is almost completely discharged, the VT1 transistor is closed, switching off a call. At the face values of resistors specified on the circuit and condensers duration of a sound signal - more than a minute.

the Main function of the R1 resistor - to limit a current at a casual touch to the wires going from a signaling device to an alarm clock, or their connection with the earthed subject. This resistor will save from serious consequences and in case of breakdown of one of condensers.

the Problem of the VD3 diode - not to allow tension "perepolyusovka" on the C2 condenser. For lack of the diode it can result from charge redistribution between condensers after network shutdown.

the Signalling device is accurate in the case of the charger of the cell phone. The printed-circuit board available in it is replaced shown on fig. 3 with the details of a signaling device established on it. Condensers - import, resistors - MLT-0,5 or others with limiting working tension not less than 350 V.Stabilitron - any low-power with tension of stabilization 5... 15 In (no more admissible tension a VT1 transistor lock source). Diodes 1N4007 it is possible to replace domestic КД105Г or others vypryamitelny with admissible return tension not less than 600 Century

of the Fig. 3. The printed-circuit board

Unfortunately to find equivalent domestic replacement to the field BS170 transistor it was not possible. It is possible to try to establish instead of the field transistor bipolar as it is made in the device described in a note mentioned above. However in this case it is necessary or to apply the transistor with very big (some hundreds) static factor of transfer of a current of h _21Ø , or to reduce face values of resistors R2, R3 that will lead to proportional reduction of duration of a signal. To use the compound transistor it is not recommended, as too big power failure on it abroach can lead to failure of a call of an alarm clock.

is necessary to find p 1 points shown on fig. In an alarm clock And and B (S1 - the switch of a call, SF1 - the contacts of a clockwork which are becoming isolated at the moment of operation of an alarm clock). It is quite good to be convinced that connection by their piece of a wire leads to giving of a sound signal. It is necessary to determine by the voltmeter polarity of tension between these points and, observing it, to connect a signaling device.

the Assembled device include p in any free socket. The alarm clock can continue to carry out the main function - to call at the scheduled time. A signal of loss of tension alarm clock operation will serve in a network in inopportune hour as

Certainly, as a source of a sound signal it is possible to use not only an alarm clock, but also, for example, a pyezoizluchatel with the built-in generator and the independent power supply, electronic knot from the sounded nursery of a toy, etc.

the Author: А.СЕРГЕЕВ, Moscow

/>!>