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Last Updated on: Tuesday, October 14, 2014 06:34 AM

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More  Beeper & Buzzer  Circuits    Doorbell Circuits

Star Trek Doorbell 

In the Star Trek “Next Generation” TV series, the doorbell outside the private quarters of a crew member makes a particular “beep-boop” sound.  The 3v battery powered circuit below tries to simulate this sound. The circuit uses one 74HCT74 dual D flip/flop IC, wired as two one-shot circuits.  Both are designed to produce a pulse about one half second long.  The first pulse turns on a 555 timer to form the beep sound. 
The second flip/flop one shot turns the 555 timer circuit and turns on an n-channel FET, which switches in an extra capacitor, to make the “boop” sound.  To my ears, I think the beep sound is right around 2KHz, while the boop sound is about 10% lower at about 1.8KHz.  A variable resistor sets the beep sound frequency. The output of the 555 timer feeds a low power 8 ohm speaker using a buffer n-channel FET. A diode “or” gate and another FET enables the speaker and time circuit.  Each time the pushbutton switch is pressed, the circuit should produce the beep-boop sound.  I have observed that some 74HCT74 ICs do not always operate correctly in this circuit.  Some devices have a poor Schmitt trigger action on their inputs.  Let me know if you have problems.

Click on Drawing Below to view PDF version of Schematic

StarTrek Door Entry Sound

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