Sumovore Manual

The Solarbotics Sumovore
Building the Edge / IR Transmitter Electronics - 6
Step 25 & 26 - Installing and anchoring the 20k Trimpot:
The “trimming potentiometer” is known in the electronics biz as a “trimpot”, so
get used to the term. This adjustable resistor tunes the 555 timer so we can ‘dial
in’ exactly how on-tune we want the IR emitters transmission frequency. We want
this ability because there’s a natural variation in the manufacture of parts, which
means that no two resistors or capacitors (even if from the same batch) will
measure exactly the same value. Because of this variation, we need the trimpot to
let us fine-tune the circuit.
There are occasions when we will want to de-tune the circuit to make it less
sensitive, like in low-light levels when the IR sensors are very responsive and see
targets over 4 feet away, or the reflection off the sumo ring surface. Having the
trimpot handy on the edge of the PCB for tuning your circuit will be very useful
indeed!
Find your trimpot, and bend the legs down as shown in the illustration. Install it
into the position marked ‘TP1’.
To anchor your trimpot, find a boat anchor, tie it to your trimpot, and heave’er over the side into the
deep blue sea... no, no, no. What we mean by ‘anchoring’ is to lock the trimpot down so it doesn’t
wiggle around while you are tuning it. You can easily break off the trimpot if you don’t. This is
IMPORTANT, so don’t skip this step even though it looks... skippable. It isn’t. Do it, or we’ll tell your
Mommy on you.
Find one of the longer resistor clippings from your past assembly (yes, even if you have to carefully dig
in the trash), and use it to straddle the trimpot. Solder it in place, so the clipping holds the trimpot
snuggly down in place. See? That wasn’t so bad.
Step 25: Bend the legs down,
then install at ‘TP1’
Steps 26: Trimpot Anchored
Step 27 & 28 - Capacitors and Transistor
To function properly, the LM555 timer chip also needs a
pair of capacitors. The two 0.001µF (labled ‘102’)
capacitors (look for a ‘102’ stamped on the side) are not
polarity sensitive, so stick them in at positions ‘C9’ and
‘C10’, and solder them down.
The PN2222 is used to amplify the small signal out from
the LM555 timer to the two infrared LEDs you’ll be
installing. The transistor is polarity sensitive, so install it so
the curved shape of the transistor matches the one printed
on your circuit board. Remember, clean soldering counts,
so don’t cause any accidental shorts on the close
transistor solder pads.
Step 27: 0.001µF capacitors
to ‘C9’ and ‘C10’
Step 28: PN2222
Transistor at ‘Q1’
Steps 27 & 28: Capacitors and Transistor
This is what it should look like after
Capacitors and Transistors are
installed
Steps 25: Preparing and Installing the 20k Trimpot