Economical battery operated timer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Economical battery operated timer. 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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This timer is convenient to use where there is no stable power supply. It allows you to save battery power, because immediately after the end of the set time delay, the timer automatically switches to standby mode. The countdown of the time interval is accompanied by "ticking", which informs about the normal functioning of the device.

The timer provides a countdown of time delays from 1 to 99 minutes. Its schematic diagram is shown in fig. 1.

(click to enlarge)

The device consists of a timing unit, sound alarm elements and a shutdown device. The timing unit includes a quartz oscillator with a frequency divider on the DD1 chip, a two-decade decimal counter on the DD2 chips. DD3 and the initial installation circuit on the elements R3, C3.

Let's take a closer look at how the timer works. When the contacts of the switch SA1 are closed, the supply voltage is supplied to the trigger on the elements DD5.1, DD5.2. which, by connecting the capacitor C5 to its input, is set to the log state. 1. As a result, the transistor VT2 opens. power is supplied to the microcircuits DD1 - DD4 and the countdown begins, set by the switches SA3 (tens of minutes) and SA2 (units of minutes). At the same time, on the output 12 DD4 chips will be the log level. 0, and on pin. 11 - log level. 1. Pulses with a frequency of 4.4 Hz pass through the element DD1 to the base of the transistor VT2. 6 microchips DD1. These pulses are in the form of a meander, so the BF1 emitter, connected to the collector of the transistor VT1, emits clicks at a frequency of 4 Hz. perceived by ear as a characteristic "ticking".

At the end of the time delay on both moving contacts of the switches SA3 and SA2. and then on the output. 3 elements DD4.2 and pin. 12 element DD4.3 chip DD4 appears log level. 1. Element DD4.3 passes a signal with a frequency of 1024 Hz. Through the element DD4.4 and the transistor VT1, it enters the emitter, which starts to give intermittent tones. The signal continues for one minute, after which the negative voltage drop at the output of the element DD4.2 through the differentiating circuit C4R9 switches the trigger on the elements DD5.1. DD5.2. Transistor VT2 closes, removing power from the timing unit and the sound alarm elements. The timer goes into standby mode. Current. consumed by it in this mode is approximately 4 μA. To restart the timer, turn off the power using the SA1 switch and turn it on again after a few seconds.

When assembling the timer, resistors KIM (R2) and MPT-0.125 (the rest) were used. The K176IE8 and K176LA7 microcircuits are interchangeable with similar K561, 564 series. The ZQ1 resonator can be any at 32768 Hz, even with a frequency deviation of several hertz from the specified nominal value. Another piezo emitter is also suitable, but in this case, a decrease in the volume of the Sound is possible. Switches SA2, SA3 - PP10, SA1 - any small. In the absence of PP10 drum switches, it is permissible to replace them with biscuit or P2K push-button switches with mutual switching off. To power the device, you can use the battery "Korund" and its foreign counterparts. The operability of the device is maintained when the voltage drops to 6 V.

The timer parts are mounted on a fiberglass printed circuit board with dimensions of 65x52 mm (Fig. 2). Switches SA2 and SA3 and emitter BF1 are installed on the same board. The latter is fixed on the side of the printed conductors parallel to the board and is isolated from it with a thick cardboard gasket.

Economical battery operated timer

The protrusions of the ZP-3 body are soldered in convenient places to the common wire track. The unused inputs of the DD5 chip are connected to its pin 14.

The case of the timer is made of foil fiberglass. The dimensions of the walls are chosen based on the dimensions of the board and switches. Inside the case, it is necessary to provide a compartment with a removable cover for placing the battery. The front side of the switches (drums and windows with numbers), as well as the SA1 switch, are displayed on the front panel of the device. Holes were made in one of the side walls opposite the BF1 emitter.

A timer assembled from serviceable elements should work immediately. If, after turning on the power, there will be no clicks of the piezoelectric emitter, you should check the supply voltage to the microcircuits DD1-DD4. and then the operation of the crystal oscillator. In the absence of generation, it may be necessary to select one of the capacitors CI, C2, or both at once. The desired volume of clicks of the piezo emitter is set by selecting the resistor R7.

To change the sounding time of the tone signal at the end of the shutter speed, you can use a waiting multivibrator made on two free elements of the DD5 chip (not shown in the diagram).

Resistor R6 and transistor VT1 can be eliminated by connecting the emitter to the output of element DD4.4 directly or through resistor R7.

Author: D. Nikishin, Kaluga

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