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EDF1• 4
INTRODUCTION
Have you ever had a project that you needed an alarm or alert signal for, but
you were tired of the same old “beep beep”? Have you ever made an
annoyance alarm to surprise that special someone, but the sound just wasn’t
irritating enough? Well, help has arrived! The Ramsey EDF1 will provide you
with a small, easy-to-mount noisemaking solution to fill all your unique
auditory needs. All you need to do is connect a small 8 ohm speaker and off
you go!
EDF1 CIRCUIT DESCRIPTION
This is a fairly simple circuit, and pretty easy to follow even for a beginning kit
builder. The kit is built around a one-transistor oscillator made with Q1. This
oscillator is underdamped and is “struck” into oscillation by briefly raising the
voltage between R10 and R5. After the voltage between R10 and R5 returns
to normal, the oscillation dies out, as shown in the picture.
The effect is an exponentially decaying sine wave. An NE555 timer provides
the “striker” that gets the oscillator going. Every second or so the NE555
outputs a pulse that appears at the junction of R10 and R5. Then Q1 outputs
the waveform above which is fed to an audio amplifier. The result is an
output that sounds like a faucet drip or sometimes maybe a guitar string
pluck.