Scheme that generates large delays. Scheme, description

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Scheme that generates large delays. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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Longer RC time constants have to be applied to obtain a waiting multivibrator pulse duration that exceeds minute intervals.

The circuit shown in the figure, assembled from three ICs and multiplying the pulse duration of the waiting multivibrator, generates delays of up to 160 minutes using a 715 kΩ resistor and a 1 uF capacitor.

(click to enlarge)

The circuit can generate large delays without increasing the values of R and C.

After turning on the circuit, the counter U1 is set to zero and remains in this state until a low potential is applied to its input. At a low potential at the input, the counter U1 starts counting the negative edges of pulses with a frequency of 1 Hz, which are generated by the self-oscillating multivibrator U2. As shown in the figure, in order to obtain a given delay, it is necessary to connect the corresponding output of the counter to the input of the gate U3-a.

After the counter U1 counts the number of clock pulses required to form the specified delay, a high potential is set at the output selected with the jumper, which resets the multivibrator U2. In turn, this leads to a drop in the potential at the output of the circuit. The circuit remains in the specified state until the low potential is removed from its input.

To obtain longer delays, it is necessary to include an appropriate divider between the output of the multivibrator U2 and the input of the clock counter U1.

Author: Samuel C. Creason; Publication: N. Bolshakov, rf.atnn.ru

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