555 tri-state acousto-optical logic circuit

  
As illustrated, 555 and R4, R5, C1 and so connected as a controllable multivibrator mode, which force reset terminal 4 feet to explore pen, control terminal 5-pin external level high and low logic level input related.
555 tri-state acousto-optical logic circuit - schematic

When the probe A floating, VT1 off, added to 5 feet voltage Vdd, 555 multi-harmonic oscillator circuit can not afford, was 3 feet high, LED light, silent; when the probe A logic "1" VT1 saturated conduction, 5 feet lower than the potential Vdd, 555 oscillation, the oscillation frequency depends on the value of R4, R5 and C1. Oscillation frequency icon parameter is about 1000Hz, audible signal; when the probe A logic "0", 4 feet since the low, 555 is forced to reset, silent and dark.




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