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DiscoverCircuits.com -- Hobby Corner
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Switch Circuits, Musical
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Band Drummer’s Microphone Switch August 28, 2011 |
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I
received an email from guy who plays drums for a small band. He wanted a simple
way to turn on and off his microphone with just a tap of his drum stick onto a small
box. The circuit below performs this task with the aid of a piezoelectric device
as a shock sensor and a small dual coil latching relay with two sets of contacts.
The contacts can be wired any number of ways to a microphone circuit. I show one
circuit which should work on both dynamic and condenser mics. It should mute the
mic without producing a pop sound. |
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The circuit is powered by a 9v battery.
It draws nearly zero current in standby mode. The mechanical shock of a drum stick
hitting the box causes the piezoelectric wafer to produce a number of voltage
pulses. If the pulses reach the 4v peak mark, they are high enough to trigger
the one shot circuit, which uses a CD4013 dual D flip/flop. The one shot
circuit lasts about a half second. Its output is connected to the second
flip/flop inside the 4013 package. The resistor R2 defines the tap
sensitivity. The second circuit is configured as a classic on/off toggle.
Each time the one-shot fires, the second flip/flop changes state and stays in that
state until the next strike of the drum stick to the box. The Q and the
inverted Q outputs of the flip/flop are connected to two pulse generator circuits,
which are tied to gates of two FETs. |
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Each time the flip/flop changes state,
the two pulse circuits either latch or unlatch the relay. It takes a pulse of
only 25ms to latch or unlatch the relay.
I
would suggest that a CD4013 from Texas Instruments be used. Many 4013s from
other manufacturers do not contain a Schmitt trigger function on their inputs.
A Serpac box from Mouser, part number 635-211-I-G is just right for this
application. It is about 4 inches long and 2.6 inches wide. It has a
nice compartment for a 9v battery. The piezo wafer is glued to the bottom of
the box, which also has the 8v battery compartment. The box is mounted top
side down. |
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Serpac Box |
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Click
on Drawing Below to view PDF version of Schematic |
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