Time relay with shutdown indication. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Consumer electronics
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Only three microcircuits and several other elements will be required to assemble a simple time relay that can be used to disconnect various household devices from the network. Duration of exposure time relay is from 3 to 120 minutes. It can be set by switch SB2 (roughly) and variable resistor R5 (fine).
The device circuit consists of the actual time relay (DD1.1); clock pulse generator (DD1.3, DD2.1), generating pulses with a frequency of 1 Hz; audio frequency generator (DD2.2, DD2.3) and counter (DD3).
To start the time relay, you must press the SB 1.1 button, which is paired with the mains switch, thereby discharging the capacitor C1. After releasing the button, the timer will start to work. The capacitor C1 will be charged through the resistor R2 or the chain R3 - R5 (this depends on the position of the switch SB2). As soon as the voltage at the inputs DD1.1 reaches the switching threshold, the output of the element will appear logic level "1" and start the generator on the elements DD1.3, DD2.1. At the output of DD2.1, pulses with a clock frequency of 1 Hz will follow.
The key on the transistor VT1 is needed to control the VD1 LED, which will flash at the same frequency. Pulses with a frequency of 1 Hz also control the audio frequency generator. An amplifier on a transistor VT2 is necessary to match the output of DD2.3 with a telephone capsule BF. The generator generates pulses with a frequency of about 1 kHz. To delay the shutdown, which warn VD1 and BF, is the counter DD3. Clock pulses are fed to its input C. Capacitor C4 and resistor R7 are necessary to set the counter to zero.
After the fifteenth pulse arrives, a logical "1" will appear at the output of the counter and, through the inverter DD1.2, will close VT3, thereby turning off relay K1, and it, in turn, will turn off the load and power of the time relay. If necessary, extend the shutdown delay time outputs DD1.2 can be connected to pin 12 of the counter DD3. In this case, the delay will be 31 pulses, that is, 31 seconds. In mode "1" exposure is from 3 to 40 minutes, in mode "2" - 40 - 80 minutes and in mode "3" - 80 - 120 minutes.
The time relay uses resistors MLT-0,125, MLT-0,25, capacitors K50-35, MBM or KM. Transistors VT1 and VT2 - any of the series KT315, VT3 - KT602, KT815. Microcircuits can be replaced with K561LA9, DD3 - with another similar counter, but you will have to change the drawing of the printed circuit board. Phone capsule BF - any with a winding resistance of 100 - 1000 Ohm. Switches SB1 - type P2K without fixation, SB2 - P2K for 3 switching groups.
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