Currently widespread e-TRAVEL CLOCK and similar watch with a miniature buzzer as the sound source - reminders of the occurrence of the deadline. However, small volume regular signal, as shown, is often insufficient for to Wake, for example, soundly sleeping person.
I have also developed connecting an external sound projector capable significantly improve the efficiency of an electronic alarm clock. Collected such device based on Electromechanical door call (GOST 7220-66), in addition to having a network of regular low-voltage winding for connection the buttons, which was also fitted with electronic transistor key and relay sealed contacts (reed switch) in the load circuit. And the structure used here, the relay is a special, so-called magnetic the fixation.
The fact that this device apart from the coil with a reed switch there and the polarizing field source is a permanent magnet. Magnetodynamic force (MMF) the absolute latest the magnitude but not enough to trigger the relay, but it is acceptable to save contacts in drawn together position. In the result eliminates the need for a constant current flow through the coil if you hold the relay in closed condition.
Relay switches on from a sufficiently intense pulse, which MDS generated by the coil is formed with the field magnet so that the total the result exceeds the threshold of the reed switch. Thereafter sealed contacts remain attracted to each other (closed) indefinitely without feeding energy from the outside.
For releasing this relay requires MDS reverse of the sign in relation to the field magnet when the resultant force becomes less than the threshold release the reed switch. This situation can be created in various ways. For example, the inclusion of additional coils are wound, as in the two-position relay series CPF, in the opposite direction. In recommended same design, everything is solved much easier is using an external permanent magnet brought to relay.
In standby mode (when the signal from the base clock is not supplied) finishes the secondary winding open call and they are present In about 12 the AC voltage. Rectified by the diode VD3, it is used for to power the circuit. That is, electromagnetic "filling" call works as power transformer with half-wave rectifier in the secondary coil.
Schematic, PCB layout and installation "loud-voiced" prefix to electronic alarm type TRAVEL CLOCK
When the alarm on a regular buzzer pulse appears the rectangular voltage with a frequency of about 1 kHz. Through a chain VD1R1C1 it is fed to the base of VT1, thus opening the circuit of the electronic key. As a result of increased collector current of the transistor. This leads actuation of relay K1, contact To 1.1 which, like zvonkova button completing the low-voltage winding. And along with the weak buzzer regular hours begins to ring loudly door elektrozvonka is automatically connected to this makeshift console. Well, VD2 diode prevents "break" transistor disabling of the relay coil.
With the closure of the reed switch, the voltage at the input of the rectifier becomes zero, that is, the scheme actually is disconnected from the power source. However sealed contacts remain firmly attracted to each other, because to hold the relay in this state, no energy supply is not required. The call will continue to ring in full until such time as awake user unlocks relay external magnet, leading the switch is the original open position.
Important note. If the signal is received from the base hours not ends, the scheme once unlocked, you can re-starts. Given this circumstance, the user has not to rush the magnet. His help, you can resort only thoroughly rousing himself from sleep. And such awakening inevitably occurs, as practice shows, only the termination of a long regular buzzer.
The scheme is not critical to the choice of the majority of the details. Diodes VD2 and VD3 can be direct current of at least 30-50 mA and reverse voltage it's about 50 (e.g., CD, CD, CD, CD, CDA, KDV, KD522). Acceptable also CD, D7, D226, D-D, D, D, and other D semiconductor gates with appropriate parameters, but their application entails redoing the PCB.
Approach to VD1 more stringent. It is desirable that the selected diode had a small forward voltage (e.g. germanium, type D9). Otherwise it is difficult to guarantee the reliable operation of the device, especially when partially a low battery basic hours.
The VT1 transistor must have h21e > >40...50,Ik max >= 25 mA, IKE max>=25 V. Such parameters are, for example, KT315, KT361, CT, MP, MP, MP, MP, MPA, MPB, MPA. When using the p-n-p transistors I need to change to the opposite polarity as the inclusion of diodes, so and connecting the input device to the buzzer base hours.
Relay self-made, assembled, based on serial magnetic switch CAM-2. The coil is from 1500 turns PAW-0.1. It is wound on a frame of thick paper and put on the switch. To create a polarizing field use small-sized permanent magnet (for example, from reed button).
The main part of the device mounted on a printed circuit Board, which is made in advance of the 1.5-mm foil Micarta or phenolic resin by cutting respective insulating grooves in the conductive layer. Resistors ULM, diodes CD and D9 is installed vertically. The findings of the transistor KT315 and condenser km solder, being careful not to deviate from the recommended topology. Well, when you use the details of other sizes made in charge the appropriate adjustments.
The cutout on the motherboard is for the relay coil. In the place circled on the sketch dashed line, glued a magnet. Correctly mounted Board is placed in the housing, which can be a suitable plastic box sizes; through the holes in one side shows four flexible wire type mgshv-1.
A couple of conclusions that goes in accordance with fundamental electrical and installation diagrams to the base clock, is connected to the contacts of the buzzer with the correct polarity, which is useful in advance to clarify with tester. And all because the manufacturers of cheap "electronics" often sin error in the legend of details on their products. True the polarity of the voltage at the terminals of the buzzer is determined by the deflection connected voltmeter at the time of arrival of the sound signal from alarm, yet coupled with the prefix. The very same can dock run all-in-one, connecting the wires to the contacts of the buzzer, or split, for which the watch is set microresearch, and the entrance the console is equipped with microvilli (illustrations plug-forklift variant not shown).
Configuring the IED is to select the optimal placement magnet, which are gradually moving towards the reed switch. In the moment of "clumping" sealed contacts note the location of magnet. Then it slowly begins to push on far enough for the opening of the reed switch. Equidistant from these "critical areas" and you'll be optimum, where the magnet is glued to the Board.
The value of the resistor R2 is selected for reliable relay operation. However, not you should get involved with searching too the small resistance, because it can lead to emergence of extremely large collector current when operating transistor VT1.
Author: Dmitry Volkov