Time relay. Scheme, description

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Time relay. Radio - for beginners

Radio - for beginners

Time delay relays, also called timers, are designed to automatically turn on and off the power of various devices after a predetermined time. Such electronic machines are most widely used in photo printing, to turn on household appliances powered by an electric lighting network for a certain time, which eliminates excessive power consumption.

The proposed time relay on digital microcircuits familiar to you is powered by AC and allows you to set such time delays in three subranges: from 0,05 to 12,5 s every 0,1 s; from 0,5 to 127,5 s every 0,5 s; 0,5 to 127,5 min after 0,5 min. The time delay accuracy depends on the stability of the alternating current frequency of the electric lighting network.

Schematic diagram of the time relay is shown in Fig. 1.

Apart from the power supply, it is formed by the following main components: pulse shaper, exemplary time interval shaper, pulse counter, decoder, control and controlled devices. Of the eight microcircuits operating in it, six are pulse counters K155IE2, K155IE4 and K155IE5. You are already familiar with the first of these microcircuits, and you will have to get acquainted with the other two.

The pulse shaper is a Schmitt trigger, assembled on the elements DD1.1 and DD1.2. Through the capacitor C1 and the resistor R1, a pulsed voltage with a frequency of 100 Hz is applied to its input, taken from the resistor R9 connected to the output of the full-wave rectifier VD4 of the power supply. As a result, at the output of the Schmitt trigger (pin 6 of the DD1.2 element), rectangular pulses with a frequency of 100 Hz are formed, which are fed to the input of a four-stage shaper of exemplary time intervals. Counter DD2 divides the input pulse frequency by 10, DD3 by 10, DD4 by 6 and DD5 by 10.

As a result, at the output of the first counter of this circuit, a signal with a frequency of 10 Hz is formed, at the output of the second - 1 Hz, and at the output of the entire shaper - with a frequency of 1/60 Hz. Select one of these exemplary frequency values corresponding to the exemplary time intervals of 0,1 s, 1 s and 1 min, switch SA1 "Multiplier".

The counter of pulses coming (through switch SA1) from the exemplary time interval shaper is formed by counters DD6 and DD7 connected in series. From their outputs, the pulses through the contacts of the toggle switches SA2-SA9 "Excerpt" are fed to the inputs of the logic element 8I-NOT DD8. In the described device, it performs the function of a decoder - a low voltage level at its output, which serves as a signal for the end of the time delay, appears only when there is a high voltage level at all its inputs.

The required exposure time is set by the SA1 switch and toggle switches (or latching pushbutton switches) SA2-SA9. So, for example, in order for the shutter speed to be 1,6 s, the switch SA1 must be set to the "X0,1s" position and the contacts of the SA7 toggle switch should be closed (0,1X16 = 1,6s). As soon as the input pin 6 of the decoder receives a high-level pulse from output 2 of the counter DD7 (at this time, all other inputs of the DD8 element are free, which is equivalent to applying a high-level voltage to them), a low-level voltage will appear at its output, which will switch the control device and stop the time relay.

The function of the control device is performed by an RS flip-flop assembled on elements DD1.3 and DD1.4. When you press the SB1 "Start" button, the trigger is set to a single state - a high-level voltage appears at its direct output (the output of element DD1.3), which opens the transistor VT1, which is part of the actuator. As a result, the electromagnetic relay K1 is activated and with its contacts (not shown in the diagram) turns on the electrical appliance.

At the same time, the low-level voltage from the inverse output of the trigger acts on the R input of all counters and sets them to their initial state. From this moment the time delay starts. If, for example, the contacts of the SA7 toggle switch are closed, and the SA1 switch is set to the "XI s" position, then after 16 s a low level voltage will appear at the output of the DD8 element, which will switch the RS flip-flop to the zero state, causing the transistor VT1 to close, the electromagnetic relay K1 will release the anchor and disconnect the appliance from the mains.

In general, the toggle switches SA2-SA9 "Exposure" allow you to significantly expand the range of time delays - from 0,05 s to 127,5 min. For example, when the switch SAl is set to the "X1 s" position and the contacts of the toggle switches SA3, SA4 and SA5 are simultaneously closed, the exposure time will be 7 s, and when the switch SA1 is set to the "XI min" position and the contacts of all the toggle switches SA2.-SA9 are closed, the exposure will reach 127,5 min. But, as the practice of using such a device shows, usually one of the eight toggle switches is enough to select the required time delay.

The pulse shaper with a shaper of exemplary time intervals, a counter with a decoder, a control trigger and a transistor VT1 with an electromagnetic relay K1 can be mounted on one common board (Fig. 2), and the power supply can be mounted on another board, which will make it possible to most rationally place them in a suitable finished or homemade box. The mains transformer of the device can be the same as in the power supply of the digital frequency counter described below.

Time relay
Rice. 2 Timing relay circuit board

Place all toggle switches and switch SA1 "Multiplier" on the front panel of the time relay box and make inscriptions next to them corresponding to the functional purpose.

Electromagnetic relay K1-RES47 (passport RF4.500.409 or RF4.500.419) or another similar, reliably operated from a DC source with a voltage of 10 ... 12 V.

Mounting parts on the board can be either printed or wire - it all depends on the available materials and experience. It is advisable to place the conductors of the power supply circuits of the microcircuits on the board from the side of the microcircuits (in Fig. 2 they are indicated by continuous lines crossing the printed conductors), which will reduce the number of jumpers during printed wiring, and when wired, it will eliminate accidental short circuits of the conductors at intersections.

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