Digital time relay. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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The proposed time relay (Fig. 1) is built on a digital principle and allows you to get long exposures with high stability.
Fig.1 (click to enlarge)
After pressing the S1 button, the trigger switches on the elements D1.1 and D1.2, the level "1" at the output of the element D1.1 will allow the passage of clock pulses through the element D2.1. The first of them will switch the trigger-former of the output signal on the elements D1.3 and D1.4 to a single state and through the element D3.1 will go to the counter, after which the countdown will begin.
The trigger counter on the D4-D10 microcircuits and the D2.2 element operate in the subtraction mode. The required dwell time is obtained by setting the switches S2-S7 to the desired positions (the sum of the numbers corresponding to the positions of the switches is the dwell time in clock cycles).
The level "0", which occurs at the output of the element D11 after the end of the exposure time, sets the flip-flops on the D1 chip to the zero state. In this case, the clock pulses stop passing through the element D2.1, and the level "3.2" will be formed at the output of the element D0, which will switch all counter triggers to the zero state.
A positive voltage pulse from the output of element D1.3 is fed to the base of transistor V2, in the collector circuit of which relay K1 is connected. Relay contacts K1.1 include a photographic enlarger lamp or other actuator.
Transistor V2 and its supply voltage are selected depending on the parameters of the installed relay K1. In this case, relays RES-9 (passport RS4.524 202P2 or RS4 524 215P2), RES-10 (passport RS4.524. 303P2 or RS4.524.312P2), etc. can be used. Relay contacts must be rated for voltage and the current of the controlled circuit. The resistance of the resistor R3 *, providing the saturation mode of the transistor, must be at least 6,2 kOhm.
A diagram of a simple master oscillator, which is a multivibrator, is shown in Fig. 2.
Ris.2
With the capacitance of capacitor C1 indicated on the diagram, the pulse frequency is 1 s. More precisely, the frequency is obtained by selecting one of the resistors R1* or R2*.
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