writes:
Here is the overall design.
The sensor consists of (2) geophones. They are places aprox. 30-40 feet
apart on a known trail that illegals use.
The prototypes we are using have (2) LT1677 opamp circuits that amplify
the geophone outputs and feed the signal into a basic stamp 1. The level
of signal isn't converted to digital, the signal when large enough (about
1.67 volts) will drive the input pin high and thus we have a logic
switch.
In order to limit false hits the software in the basic stamp listens for
a hit on a geophone. When there is a hit it basically says if the second
geopghone is hit within the next 2 seconds cancel the entire hit becuase
it is most likely rain or some other seismic disturbance. If the gephone
is hit after that to seconds the it is a real hit and send a signal back
to us through our repeater. The data coming to us tells us what "port"
hit first and what sensor it is. By knowing what port was hit first we
can tell what direction the contact is going.
During initial powerup we callibrate the instrument by "walking the line"
or walking by both geophones. By doing this and counting the number of
footfalls on an average man we can the have a rudimentary counting of the
number of people walking by. By dividing the number of detected footfall
by the number of detected footfalls in the calibration we have the number
of intruders. It all works but the noisy circuit is killing me.
This system works but our circuit is noisy and when I make the software
just send hits on either geophone as they come in, sometimes, at random,
one or both of the "ports" will show hits for minutes on end. If I touch
the circuit board with my finger i can kill the noise until some kind of
seismic activity start the noise again.
Michael S. King
Technical Director
Seems to me that if all you are doing is checking a trail, you
could use an IR beam. Another thing you could use is the
Polaroid ultrasonic range finder they used on their Land
cameras, which I think is still available as an experimenter
kit. It has a range of about 30 feet, and might even keep
animals away.
You could even mount such devices right onto the barrel
of the machine gun and, in the case of the beam detection,
set it to fire immediately with almost certain lethality. You
would also need a hidden mechanical arm and claw that
would then pop out, grasp the corpse and drop it into a
pit, then swing back and deploy a rake to smooth over
the killing zone... perhaps even sprinkling a little fresh
sand over the area to cover any blood stains.
Refer to "The Architects" skit for further ideas...
On Wed, 9 Apr 2003 10:02:47 -0700 "Michael King" <
Mike@.........................
>=20
writes:
Here is the overall design.
The sensor consists of (2) geophones.&=
nbsp; They=20
are places aprox. 30-40 feet apart on a known trail that illegals=20
use.
The prototypes we are using have (2) =
LT1677 opamp=20
circuits that amplify the geophone outputs and feed the signal into a =
basic=20
stamp 1. The level of signal isn't converted to digital, the signal=
when=20
large enough (about 1.67 volts) will drive the input pin high and thus we=
have=20
a logic switch.
In order to limit false hits the =
software in the=20
basic stamp listens for a hit on a geophone. When there is a hit it=
=20
basically says if the second geopghone is hit within the next 2 seconds =
cancel=20
the entire hit becuase it is most likely rain or some other seismic=20
disturbance. If the gephone is hit after that to seconds the it is =
a=20
real hit and send a signal back to us through our repeater. The =
data=20
coming to us tells us what "port" hit first and what sensor it is. =
By=20
knowing what port was hit first we can tell what direction the contact is=
=20
going.
During initial powerup we callibrate the=
=20
instrument by "walking the line" or walking by both geophones. By =
doing=20
this and counting the number of footfalls on an average man we can the =
have a=20
rudimentary counting of the number of people walking by. By =
dividing the=20
number of detected footfall by the number of detected footfalls in the=20
calibration we have the number of intruders. It all works but the =
noisy=20
circuit is killing me.
This system works but our circuit is =
noisy and=20
when I make the software just send hits on either geophone as they =
come=20
in, sometimes, at random, one or both of the "ports" will show hits=
for=20
minutes on end. If I touch the circuit board with my finger i can =
kill=20
the noise until some kind of seismic activity start the noise=20
again.
Michael S. King
Technical DirectorAmerican=20
Border Patrol