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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, June 01, 2021 03:06 PM
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Star Trek Doorbell
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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. |
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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. |
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Click on Circuit Below to view PDF of Schematic |
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eMail David A.
Johnson, P.E. about this circuit |
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