Build a Better Mouse Trap
sound level of 90-100 dB.
With the circuit shown in
Schematic 1, you will get at least one
month of continuous use with one set
of rechargeable batteries. While I have
successfully used alkaline batteries,
they will deliver about 6V when
new. This is .5V over the rated voltage
of the Athena. While I have yet to
blow an Athena this way, it is not recommended. If you use rechargeable
batteries, you will get 4.8V to 5V from
a freshly charged set. It’s something
to keep in mind.
Note that the schematic shows a
VEX servo. You can use a standard
servo, as well.
R1 is the two ohm resistor
connected between the servos Vdd
and the relay. This will keep the servo
from resetting the microcontroller
when first fired.
Note that a .1 µF and a 100 µF
capacitor should be connected to Vdd
and Vss as close to the microcontroller as possible.
The SPST switch (S1) is not necessary if you use a header and jumper to
provide power to the circuit, as you
can just remove the jumper when you
want to disable the system.
I used an Athena WorkBoard
PCB, as it provides ample prototype
space to connect the siren and relay.
After I placed my servo, I attached the
battery and circuit board to the top of
the trap as shown in Figure 6.
If you use one of the Kronos
Robotics boards that has a built-in
RS-232 driver, remove it during
normal operation, as it is
not needed. This will help
reduce battery drain.
■ SCHEMATIC 1
Once awake, it activates the servo by
pulling the pin, then pauses a bit and
rearms the servo. It does not technically arm the servo
since the pin is
pulled, but it does
arm the sensor. This
allows the siren
to keep sounding
as the mouse
moves up and
down the ramp.
source is called
and is included in
How Well Does it Work?
In the first week, I caught 12
ITEM PART NO.
Part no. from Kronos Robotics unless noted otherwise.
❑ Athena Microcontroller 16276
❑ Athena WorkBoard PCB 16460
❑ Athena WorkBoard Basic 16473
Note the following components can be picked up at
any electronics supply house.
■ Kronos Robotics
Refer to Listing 1. The
program is straightforward.
It sets up the I/O ports, then
arms the servo by adding a
slight amount of slack to
The main loop puts the
microcontroller to sleep. The
short from port 7 to Vss will
wake up the microcontroller.
■ KR Micros
❑ 4AA battery holder
❑ 2 ohm 3 watt resistor
❑ 390 ohm resister
❑ 10K resistor
❑ 1M resistor
❑ .1 µF capacitor
❑ 100 µF capacitor
The Athena compiler is available free at the Kronos
■ Tower Hobbies
❑ Standard Servo from Tower Hobbies
■ Control Your World Forum
forums/ viewforum.php?f= 21
❑ SSC- 32
Lynxmotion #SSC- 32
August 2007 35