using TP1 to just above or below TP2. For R1, use a 100K
ohm resistor and a 10K ohm resistor for R2. Set the rotary
switch to F for sounding the alarm when a vibration occurs.
The vibration sensor feeds into the non-inverting input
of the op-amp which was described previously. It is
amplified about 11 times and generates a voltage when
moved or jarred. R10 adds the voltage generated from R5 to
the amplifier. The piezo film generates a small amount of
voltage when bent. R8 is set just above or below the voltage
of the output of the amplifier. When the sensor vibrates, it
will cause an interrupt.
For sound applications, use a PUI POM-5238
microphone and solder it in noting the polarity. Use a 100K
trimmer resistor for R3; R3 sets the sensitivity. Short R10
with a jumper. The amplification can be adjusted by
changing R1 and R2. When sound pressure changes, the
microphone changes the voltage out. Measure the voltage
of TP2 and adjust R3 to about 2. 5 volts. Adjust R5 for the
tripping voltage using TP1 to just above or below TP2. The
sound mode functions the same as the vibration mode.
Set the rotary switch to F for when a sound is detected.
The motion detector was designed for use with any of
the new Panasonic motion detectors. The cost of the
sensors is about $9.50. They are very small and can
measure movement from distances of 10 meters. Honeywell
makes several types of digital motion detectors. Using the
template, drill out the hole called for. Solder in the transistor
socket into the pads labeled “motion.” Add a one megohm
resistor, R7. Mount the board to the chassis using only one
screw. Put the sensor through its hole and plug it into the
socket. Set the rotary switch to two to activate when motion
is detected. Set the rotary switch to three to activate when
no motion is detected.
The Panasonic motion sensors are pyroelectric sensors
that detect variations of infrared. They send the pull-up
resistor of RA5 to ground when detecting heat. R7 biases
their output. They take about 30 seconds to stabilize.
Use a 10K thermistor across pad 1 and pad 2. This can
be mounted remotely. Add a 10K ohm resistor in R4. The
R5 potentiometer is used for the tripping point by varying its
output voltage. There is a listing of voltages of the thermistor
vs. temperatures in Centigrade available at the article link.
The temperature can be changed when it is either too high
or too low by switching the rotary switch. You can measure
the tripping voltage by using TP1.
Set the rotary switch to B for sounding the alarm when
above a set temperature. Set the rotary switch to
C for sounding the alarm when below a set temperature.
With this circuit, you can substitute any resistor for the
thermistor and adjust the pot for the tripping point. Many
sensors use a change of resistance. Position sensors are one
of these. Just connect the sensor across pads 1 and 2 with
an equal resistance on R4.
Some position sensors have three terminals: positive,
negative, and wiper. Eliminate R4 and place the sensor with
the wiper on pad 2 and the other two terminals on 1 and 3.
I often make up temperature probes by using two
strands of #30 wire wrap up to 20 feet in length. The
resistance of the sensor is 10K ohms at 20 degrees C, so
the wire resistance is negligible. Twist the wire together and
wire wrap to the themistor, and solder. Take a red plastic
twist connector and remove its metal core. Push the
thermistor into the cap and use a hot glue gun to seal the
thermistor. This makes it waterproof. The temperature
software has built-in hysteresis to prevent chatter. It uses the
voltage comparator of RA1 and RA0 with an interrupt.
This is one of my favorites due to the distance
attainable. The trespass detector uses an infrared detector
with a high power infrared-pulsed emitter. It is basically an
invisible light beam that if broken, sounds an alarm.
Bend the leads of a Vishay TSOP2436 IR receiver and
place them into the three pads labeled “IR.” The lens should
be in the circle where the photodiode would go. R6 will not
be present. The specifications on these two devices indicate
they may have a range of up to 45 meters (135 feet).
You will need a 110 volt AC to five volt DC power
supply on the IR source as it is continuously on and draws
over 200 mA. Set the rotary switch to D to sound the alarm
when the IR beam is broken. Set the rotary switch to E to
activate when the IR beam light is sensed. The IR transmitter
and receiver have to be the same frequency to work
properly. The IR transmitter is pulsed at a certain frequency
to avoid false signaling from other light sources.
The IR transmitter uses four 10 degree TSAL6100 IR
emitters pulsed at 400 mA. The first one I built had a
dropping resistor which got hot. Then, it dawned on me ...
why not use four IR emitters for a broader beam and let
them perform the voltage drop? The IR emitters are pulsed
at a 36 kHz frequency for . 3 milliseconds and then turned
off for 10 milliseconds. The receiver is constantly on and
functions as a missing pulse indicator. If the beam is not
detected for more than 20 milliseconds, it alarms. Since the
unit is constantly measuring, I recommend a five volt power
supply to prevent the battery from running down. Keep in
mind that the receiver can be a latched alarm or will just
beep when the beam is broken.
The receiver pulls RA5 to ground when an IR source at
34 October 2013