For some time now, Jaycar Electronics have been selling an
attractive little module which goes by the name Aura Interactor amplifier. The
Aura Interactor was (is) intended to drive a body blaster cushion from a
computer games console or perhaps from the subwoofer signal in a home theatre
system. As sometimes happens, the product was a monumental flop and so Jaycar is
selling them off by the bucket-load at $5 each.
Buy it Here at AutoSpeed:
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As you can see, the Interactor Aura amplifier module comes in an attractively finished plastic case. It has two thumbwheel controls and two slide switches to control its operation. There are two LED indicators, one for power and one to indicate the onset of clipping.
Probably most people will just buy them and throw them into the
junk box to be "ratted" at some stage in the future. We thought that it was a
shame that such a nicely finished module should end up wasted in this way. So we
set out to draw up the circuitry and see if it has other applications.
Fig.3 shows the complete circuit and right from the outset, we
have to admit that we don’t fully understand how it functions. Nor do we have
time to fully analyse it. Hey, it could have been interesting to run it through
the Electronic Workbench simulator reviewed elsewhere in this issue. What would
the simulator have made of it? Again, we didn’t do it simply because we did not
have the time.
Let’s just run through a brief description of the circuit. The
input signal from a stereo source is coupled via a 3.5mm jack socket to switch
S2a and then via a 1μF capacitor (C7) to the volume control R44. From
there it goes to op amps U7a & U7d which provide about 75 times gain and
function as a low pass filter, rolling off signals above 2kHz.
The output of U7d drives comparator U6b which squares up the
signal and feeds it to the two flipflops in U3, a 4013 dual-D flipflop. Thus if
the output of U6b is 120Hz, for example, the two square wave outputs from U3
will be at 60Hz and 30Hz. These two signals are used to control two inputs, pins
10 & 11, on a 4051 1-of-8 demultiplexer, U4.
