Timer with 24 hour cycle. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Timer with 24 hour cycle. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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Sometimes you need to turn devices on and off at the same time during the day. For example, turn off the bell in the apartment at night, turn on the electric kettle in the morning, etc. I use this timer to automatically turn off the phone in the evening from 22 to 6 in the morning (for 8 hours), which allows me to get rid of random calls.

The timer provides, with a resolution of one minute, setting the desired time interval and repeating the process after 24 hours. The timer consists of a minute pulse generator on the D1 chip, frequency dividers with a variable division ratio D2 and D3 (16 inputs for setting the division ratio) and short pulse shapers on the elements of the D4 chip (Fig. 1.33).

Rice. 1.33 (click to enlarge)

Circuit switching is performed by a polarized relay K1. It does not require a constant supply of the winding to fix the position of the contacts, and a short pulse to the corresponding winding is sufficient to switch them.

The circuit is made on readily available CMOS microcircuits and is characterized by low current consumption, which allows, if desired, to power it from a 9 V battery. In this case, it is better to use relay K1 with a low-voltage operating voltage, for example, RPS45 RS4.520.755. 08), and then the zener diode VD4.520.755, the HL18 LED and the resistor R2 do not need to be installed, and the capacitor C1 must be increased to 10 uF.

The scheme works as follows. The timer is turned on by the SA1 toggle switch at the time from which it is required to provide a time interval. At the initial moment, when power is applied to the circuit, while the capacitor C1 is charging, a pulse is generated at the output D4 / 11, the initial zeroing of the counter D1, and the same pulse through the elements D4.2, D4.4 will switch relay K1 (relay contacts 22 and 23 closes), and at the inputs of the initial setting of the counter D2, a logical "1" will appear in accordance with the required division factor (N).

The diagram shows the position of the jumpers on the outputs D2 for an interval of 8 hours: N=8*60=480.

The division factor for another time interval can be easily determined using the relation:

N=M(1000P1+100P2+10P3+P4)+P5, где

P1...P4 - variable coefficients, called multipliers of thousands, hundreds, tens and units;

P5 - residue;

M - coefficient called the module (the diagram shows the position of the jumpers for the value M = 2).

The values of the numbers of the decimal system P1 ... P4 are set at the corresponding inputs of the counters in binary code. Thus, for a division factor of 1440: N=2(700+20)=1440 (P1=0, P2=7, P3=2, P4=0, P5=0); for division factor 480: N=2(200+40)=480 (P1=0, P2=2, P3=4, P4=0, P5=0).

As soon as a logical "2" appears on the output D23 / 1, the element D4.1 generates an impulse to switch the relay K1 (contacts 22 and 23 will open, and 12 and 13 will close). In this state, the circuit will be until the moment when a pulse appears at the output D3 / 23 (log. "1").

Counter D3 has a division factor of 1440, which corresponds to 24 hours. After this interval, from the moment the timer is turned on, a signal will periodically appear at the output of the counter for automatic switching of circuits. Depending on which group of relay contacts K1 is used, the devices can turn on or off during the day for the required time interval.

When controlling a powerful load, such as electric heaters, it is necessary to use an additional intermediate relay with the appropriate permissible current through the contacts (for a load with a power of 2000 W, current 10 A). The intermediate relay can be switched on by relay contacts K1, which are rated for a maximum current of not more than 0,5 A.

If during the timer operation it is required to turn on or off the connected device for some time without changing the timer operation cycle, then you can use the corresponding buttons: SB1 - on and SB2 - off.

When the timer is disconnected from the network, the second group of contacts of the SA1.1 toggle switch connects the winding of the VG relay K1 to the capacitor. The discharge of C7 through the relay winding will allow it to work, and it will return its contacts to its original position, regardless of at what stage of the cycle we turned off the timer. The same group of contacts through the VD1 diode will accelerate the discharge of the capacitor C1, which will ensure that the circuit is ready for operation at any time when it is turned on again.

The circuit uses resistors of the C2-23 type, capacitors C1 ... C5 of the K10-17 type, C6 and C7 of the K50-24 type for 63 V.

ZQ1 quartz will fit any type with an operating frequency of 32768 Hz (they are widely used in watches). The circuit uses polarized relays of the type RPS43 RS4.520.735-01, but many other types are also suitable, for example RPS32 RS4.520.224. The mains transformer T1 must provide a voltage in the secondary winding sufficient to operate the applied relay.

With proper installation, the configuration diagram does not require. It is convenient to check the operation of the timer when the counters (D2, D3) are supplied with second pulses from pin 4 of the D1 chip. In this case, it should be taken into account that the initial memorization of the division factor is carried out after three cycles of input pulses.

The timer circuit does not change modes during a short-term loss of mains voltage. But in order for the timer not to be disturbed during a long absence of mains voltage, it is necessary to use a backup power element (9V), from which it is enough to power only microcircuits.

Publication: cxem.net

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