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From software algorithms to material selection, Mr. Roboto strives to meet you
where you are — and what more would you expect from a complex service droid?
I always like to “wind up” on a column since it
seems rude to just jump into the questions. So, for my
warm-up … First LEGO League is getting ready to take off
now; the kids are working on the challenge field and we
are all watching the FLL site for what the challenge will
actually be — it won’t be announced until, er, a month
ago (as you read this column). The kids are jazzed and
the field has lots of intriguing robot challenges (Heart with
stent, Brain and Door – huh? Shades of “Young
Frankenstein” come to mind there!) Last month, we did
some NXC programming with the Mindstorms NXP robot,
but this month the questions are more about basic topics.
So, now that my fingers and mind are warmed up, let’s
Q. I want to use sound to trigger an action on my robot, but I’m not sure how to do it. Can you give me
a circuit that will allow my Arduino to
Any electret microphone you find will work here,
such as the Digi-Key 102-1720-ND; this part wants a 2.2K
bias resistor on the microphone instead of the 4.7K one
that I show in my schematic. I chose the 741 op-amp
because I had a bunch of them lying around and this
application isn’t too picky about this. One nice thing
about the 741 is that it is a single supply op-amp which
means it doesn’t need a plus and minus supply; just 5V
and ground works fine.
The operation of the circuit is simple. The small AC
signal from the microphone appears at pin 3 of the
op-amp which has been biased at 2.5V (halfway between
5V and ground) by R2 and R3. R4 and R1 set the gain
(about 1,000) and C3 allows only the AC component to
be amplified. The cap C4, again, passes only the AC
amplified signal through to the RC accumulator circuit
Figure 1. Sound amp circuit.
— Tony (via email)
14 SERVO 10.2010
A. Let me guess, you want a start-up for your Trinity Firefighter that will score you
extra points? As it turns out, this isn’t
too difficult but you’ll have to get a
few parts that you probably don’t
normally carry in your parts bin.
This simple circuit is made with an
electret microphone, a 741 op-amp,
and a handful of discrete parts. I’ve
made this and it works, so let’s get
going. Figure 1 is the schematic for
the circuit that I have in mind. I
used this in a Halloween prank to
make a ghost jump out when someone
yelled “Trick or Treat!” one year. Lots