Page 78 - 15 Dangerously Mad Projects for the Evil Genius

Chapter 5 ■ Balloon-Popping Laser Gun 57

Set the switch to “test” (toward the LED) and
then adjust the variable resistor until the LED is
just off, then turn it a little bit further so it is still
off. This is adjusting the sensitivity of the sensor
so it is not affected by the ambient light.
Now shine the ray gun at the balloon. When it
comes within a certain range of the phototransistor,
the LED should light. Practice aiming the laser at a
point where the LED will light, since you will
need to keep the beam on this point for ten
seconds or so to pop the balloon.

When you are confident you can do this,
position your minion next to the balloon (as an
observer) and then flip the switch to “live.” Aim
the beam at the balloon. After ten seconds or so, Figure 5-16 The can jumper
there should be a loud bang and a terrified minion.
You should then repeat the experiment from resistor, it turns on a motor that swings an arm
various distances. Resist the temptation to place around that hits the can.
the balloon popper on the head of the minion, as
The diode across the motor prevents the high
you may end up lasering the minion’s eyes.
reverse voltages you get when using a motor from
destroying the MOSFET.

Can Shooter
What You Will Need
Popping balloons is all well and good, but for
You will need the components for the can shooter
added impact the Evil Genius also likes to shoot
that are listed in the Parts Bin.
cans off the wall with his ray gun. Again, there is
some deception going on here. The can is a You do not usually get much information about
“special” can with some electronics in it. When the a small DC motor when buying one. Often, all you
beam from the laser hits the phototransistor sensor, get is its nominal voltage. The author found his
a motor swings a weight that hits the side of the motor in a local electronics store for a few dollars.
can and makes it jump. If the can is carefully You may also find one as part of a scrap toy or an
balanced, the movement will be enough to make it educational motor kit.
fall off the surface it is standing on. Figure 5-16 Look for a motor about the same size as the one
shows the can jumper, which as you might expect shown in Figure 5-21 later in the chapter. Chances
just looks like a can full of the Evil Genius’ are it should have a similar amount of power. A
favorite lunchtime snack. 4–6V motor should be fine even though we are
Figure 5-17 shows the schematic diagram for going to momentarily power it from 9V. It should
the can jumper. not have time to burn out for the small fraction of
a second it is on. However, do not be tempted to
This uses a light sensor in a similar way to the
buy a lower voltage than this because you may
balloon popper. However, in this case, when the
well burn it out.
laser hits the phototransistor turning on the
MOSFET power transistor, rather than heating a