Sometimes it is necessary to periodically enable and disable network load. Manually doing it is unlikely to suit anyone. Yes, and to manage the workload sometimes is necessary in the absence of the person. To perform such a task can offer the machine.
Before leaving on vacation, some owners leave home machine, which every evening for a few hours turns on the light in the apartment, creating the illusion of the presence of hosts [1]. Often it serves as a kind of watchdog from uninvited guests.
Another example is the failure of the compression refrigerator thermostat, resulting in either a refrigerator compartment is not cold, or the motor runs continuously and soon burns out. The way out (temporary - up to buy a thermostat, or permanent, if the refrigerator is an older model) can become automatic, periodically including a refrigerator.
A distinctive feature of the machine in comparison with published in [2] to a large range of the duration of exposure, the selection of the values of some parts can be done from a few minutes to several days. This was achieved through the use in timing chain (Fig. 1) the C2 capacitor with a double electric layer - ioniser [3]. The device has two independent regulator that determines the duration of the "Work" (R5) and "Pause" (R6).
The basis of the machine is a generator based on the operational amplifier (op-amp) DA1 controls the operation of the generator of short pulses, performed at a unijunction transistor VT1, - he, and turn, ensures the opening of the triac VS1. It feeds the generator from the mains through the rectifier diode VD5, VD6 with ballast capacitor C5. To power the multivibrator is set parametric stabilizer consisting of a ballast resistor R7 and diodes VD1, VD2.
The multivibrator is assembled by well-known scheme with ramasedi the capacitor C2 and the independent chains charge (VD3, R1, R5) and discharge (VD4, R2, R6). The capacitor is discharged and charged completely, but between two values of voltage (approximately 5.2 and 4.2 V), determined by the resistors R3 and R4 and the voltage of the shelter. This is done in order not to exceed the working voltage of the capacitor and to have the opportunity to implement small exposure at low charge and discharge currents.
The multivibrator produces rectangular pulses, the duration and intervals between them depends, as mentioned above, from the fixed resistors variable resistors. When the output of op-amp will have a voltage close to the supply (the "Work"), will begin to operate a generator for the unijunction transistor. The voltage pulses from it will flow to the control electrode of the triac - it opens at the beginning of each half cycle, and the load goes almost all the supply voltage. The pulse repetition rate much higher than the mains frequency, so the triac is stable with a load in the form of an electric motor of the refrigerator.
As for the normal operation of the triac for AC voltage at its control electrode need to apply the pulses of negative polarity, the circuit of unijunction transistor differs from traditional control electrode of the triac is connected to the emitter circuit of the transistor.
When the output Oh voltage will be close to zero ("Pause" mode), the generator will stop working and the triac will not open. The load will be de-energized.
For these in the diagram component values and a particular instance of the capacitor C2 the duration of the "Work" is defined by the formula: tp = 0,1(R1+R5)C2, and the "Pause" mode - according to the formula: tn = 0,1(R2+R6)C2. The duration of each mode can be changed from two minutes to three hours.
At the idle machine capacitor C2, of course, discharged, and immediately after turning on the timer it needs to be charged up to a voltage of about 5.2 V. This means that the duration of the first cycle of "Work" will be about R4/R3 times the installed resistor R5. For refrigerator this delay is even useful, because it will have time to gain the necessary cold. You should consider another factor associated with the first timer in the network, while the capacitor is charging C3, the device may be unstable. The best way to connect the load to the timer in 10...20 s after it starts.
In the machine, it is permissible to apply: the capacitor C2 Is K-96, K-9V; C1, C3 - K52, K50-35; C4 - km, KLS, K73; C5 - K73; variable resistors - STRs JS4 with the characteristic of A (linear); the constant - MLT, S2-33. Unijunction transistor - CTA - CTG; diodes VD3, VD4 - KDA, a VD5.VD6 - any rectifier with a permissible reverse voltage of 300 V. the Triac - COW, COG; load power up to 300 watts use it without a radiator, but if it is more (but not more than 1.1 kW) - install on the radiator of appropriate dimensions.
Most parts are on the PCB of one-sided foil fiberglass. Cost strengthen inside the housing, on the front wall of which establish the variable resistors and the socket to turn on the load.
Possible option of replacing the capacitor C5, the resistor MLT-2 resistance of 12 ohms and triac mounting on a common printed circuit Board. Diode VD6 should be removed.
The establishment timer is reduced to the selection of resistor R7 (with a running generator on the unijunction transistor) such resistance that the voltage on the capacitor C3 was a third more than at the cathode of the Zener diode VD1. If the resistance is greater than 1 kω, it is necessary to increase the capacitance of the capacitor C5.
Then spend the graduations of the scales of the variable resistors. To make it better so: measure the resistance of the resistor R1 and to determine the duration of a cycle of "Work" (to) zero when the resistance of the resistor R5, and then calibrate the scale of the resistor R5 by the formula: t=to(R1+R5)/R1 by measuring the total resistance of series-connected resistors R1 and R5. Similarly, graduate scale of the resistor R6.
To increase the duration of each cycle is necessary to reduce the charge and discharge currents, i.e., increase the values of R1, R2, R5, R6, and increase the value of the resistor R3 (this will increase the voltage, which will charge the capacitor C2, but it should not exceed the working). In addition, you should use opamps with lower input currents. For example, to increase the maximum duration of exposure to one or several days, we recommend a Zener KS147A replace XA, Oh apply CUD, the values of resistors R5, R6 to increase several times, and R3 is 10...20 times.
Parallel to the capacitor C5, it is desirable to connect a resistor of 510...750 ohms 0.25 W, and in series with C5 - current limiting resistor 36...47 Ohm 0.5 watts.
Literature
Author: I. Alexandrov, Kursk; Publication: N. Bolshakov, rf.atnn.ru