BY MICHAEL SIMPSON
3/32” in diameter. The pin
must be able to slide through
one of the holes in the truss
plate as shown in Figure 4.
The pin is attached to the
end of a piece of nylon string
(fishing line). Knot the end of
the line and pull it through the
tubing. A small drop of hot
glue will help secure it.
Originally, I thought about
some sort of light and sensor,
but I wanted something a bit more passive that would not place any additional drain on the battery. What I came up
with was a balanced plate made out of
the same truss material as the door.
I soldered a 7/32” brass tube across
the width of the truss as shown in Figure
5. The tubing is not exactly in the center,
but about 1/4” toward the back of the
truss. When flipped over, this creates a
kind of shallow teeter-totter effect. The
heavier side will face the trap opening.
The idea is to place bait on the high end
near the edge. When the mouse enters
the trap, it walks up the ramp and as it
passes the pivot point, the ramp tips.
A second brass tube is hot glued
to the base of the trap near the rear.
This tube sets under the high end of
the teeter-totter so when the ramp tips,
it makes contact with this tube. Notice
the wire that is soldered to the tube.
This is connected to the Vss side of the
interface. The brass tube connected to
the ramp is connected to the input
port on the interface. The input port
on our interface is held high. Tipping
the ramp forces the input port low.
The rest of the trap is all a matter
of taste and the materials you have on
hand. Some key points for this kind of
trap: Make the trap enclosure so that
it is only slightly larger than the width
of your ramp as shown in Figure 6.
This will keep the sneaky critters from
bypassing the ramp. Remember the
food itself has weight and should be
used to help counter-balance the trap.
When I place my food on the high
end of the ramp, I start in the middle
and slide it back until the ramp is
almost ready to trip. This allows you to
■ FIGURE 4
■ FIGURE 5
adjust the sensitivity of the trap.
I used 1/8” Plexiglas and plywood
for my trap. Strips of precut pine
would also work. It is all held together
with screws. I have found that the use
of transparent materials makes the trap
more inviting to the mice. They probably think they have an easy escape.
the pin about 1/4”. You could have just
knotted the end and placed it between
a couple of washers to work. To properly place the servo, raise the door and
put the pull pin in place. While holding
the pin in place, move the servo back
until the line is taunt. The pull pin
should be sticking through the door
about 1/16” or so. I used doublesided
tape to hold my servo in place.
In order to trip the trap, we need
to pull the pin out of the door, causing
it to fall. There are a couple ways you
can use a servo to pull the pin. Let’s
take a look at both a VEX servo and
a normal servo.
The fishing line I used was about
4-1/2” long with the pull pin on one
end and the other end connected to a
brass tube that is attached to a VEX
servo via a #6 machine screw as
shown in Figure 7.
My servo implementation was a bit
overkill as the servo only needs to pull
The standard servo is much easier to
use than the VEX. You will need a servo
arm; just about any type will do. Cut all
the points off the arm but one. Place the
arm near the center position of the servo
as shown in Figure 8. Notice that we can
use small angle brackets to mount the
servo or double stick tape.
With the servo placed near the
center position as shown in Figure 9
tie off the line. The pin end of the line
should be sticking through one of the
holes holding the door in place. Don’t
worry if you don’t get it perfect as you
can always go back and retie the line.
■ FIGURE 6
■ FIGURE 7
August 2007 33