The oscillation frequency of the multivibrator composed of IC1 (555) and R18, R19, C2 is f = 1.44 / (R18 + 2R19) C2, and the frequency corresponding to the illustrated parameter is about 2Hz. The output square wave signal is used as the shift clock pulse of IC2 and IC3.
IC2 and IC3 are 74LSl94 bidirectional shift registers, which are connected in series to form a shift register circuit. After starting, IC2 and IC3 are all cleared, Q0 ~ Q7 are all low level, the circuit is in the holding state, and the volume is minimum. When the metal sheet A is touched by hand, the S0 (pin ⑨) of IC2 and IC3 is high level, and IC2 and IC3 realize the serial right shift, so that LED0 to LED7 are sequentially lit, and at the same time, LED8 increases in brightness with the current stepwise As it increases, the resistance of the corresponding photoresistor Cds decreases and the volume gradually increases. The increase is controlled by the time of touching the A-chip. If you touch the metal sheet B with your hand, IC2 and IC3 realize serial left shift because S1 (⑩ foot) is high, and the corresponding control volume gradually becomes smaller. The reduction is controlled by the time of touching the B slice.
Under the action of the clock pulse signal, the control circuit can gradually increase or decrease the volume by touching the metal sheets A and B, thereby achieving multi-level control of the volume.
As shown in the figure is an eight-level touch volume control circuit. The controller consists of a multivibrator, a shift register, a touch control circuit, an impedance conversion circuit, etc.
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