Eight-level touch volume controller circuit diagram composed of 74L194

The figure shows the eight-level touch volume control circuit. The controller consists of a multivibrator, a shift register, a touch control circuit, an impedance transformation circuit, etc.

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The oscillation frequency of the multivibrator composed of IC 1 (555) and R18, R19, and C2 is f=1.44/(R18+2R19)C2. The frequency corresponding to the parameters shown in the figure is about 2Hz. The square wave signal it outputs is used as the shift clock pulse of IC2 and IC3.

IC2 and IC3 are bidirectional shift registers 74LSl94, which are connected in series to form a shift register circuit. After powering on, IC2 and IC3 are cleared, Q0~Q7 are all low level, the circuit is in a hold state, and the volume is minimum. When touching the metal sheet A with your hand, the S0 (⑨ pin) of IC2 and IC3 is high level, and IC2 and IC3 realize a serial right shift, so that LED0~LED7 light up in sequence. At the same time, the brightness of LED8 increases with the current in a stepwise manner. Increase, the resistance value of the corresponding photoresistor Cds decreases, and the volume gradually increases. The amount of increase is controlled by the time the porn is touched. If you touch the metal piece B with your hand, IC2 and IC 3 will realize the serial left shift because S1 (⑩ pin) is high level, and the corresponding control volume will gradually become smaller. The amount of decrease is controlled by the time the B piece is touched.

Under the action of the clock pulse signal, this control circuit can gradually increase or decrease the volume by touching the metal pieces A and B, thereby achieving multi-level control of the volume.