A handy 2-Input alarm using
This project is not
available as a complete kit.
PIC LICk-1 module is available from
Talking Electronics. You will
buy the other components from
your local electronics store.
By Mike Skypek
Our 5-Input Alarm will be available soon
as a complete kit
This article describes a 2-Input alarm developed
on the PIC LICK-1 Module
using a Microchip PIC16F628-04. The program uses the internal 4MHz
oscillator and if any other frequency is used, the timer values
will need to be changed.
2-INPUT ALARM CIRCUIT
A two zone alarm means the system has two separate detection
circuits and can
identify which circuit was triggered. The circuit uses lines RA1 and RA2
as zone 1 and zone 2.
The operator can only enable
or disable Zone 2. This allows situations such as disabling a large
zone such as the garage, while an ultrasonic detector
covering a smaller zone, such as toolboxes or equipment, remains
A more practical application would be in a small store with a
workroom at the back. The owner needs to know when someone enters the
store and specifically when someone goes behind the counter/cash
Two stage means the alarm recognizes when it has been triggered more
and reacts differently. "Warning/subdued" devices are
triggered the first
alarm is set-off and then "Intruder/loud" devices are triggered every time
thereafter. After being triggered once, the 2-Input Alarm moves to the
yellow-alert stage and uses the softer alarm outputs. Thereafter, when
triggered, it moves to the red-alert stage and uses the louder alarm
outputs. Currently both zones trigger the yellow-alert and then the
The basic 'circuit' is the PIC LICK-1 module. RA0, RA1, and
RA2 are used as input ports. RB0 thru RB7 and RA3 are used as output
The 2-Input Alarm is controlled by a single push-button that takes RA0 HIGH
when pushed. This can be a doorbell "press-button" or a small
switch mounted on the PC board.. A single 'push' does nothing, thwarting people from easily disabling the
The push-button must be pressed two times with about 1/2 second between
The push-button has three commands:
Enable/Reset the System. Push the switch twice with 1/2
second between pushes.
This enables the alarm and the indicator LEDs change from yellow to
If the 2-Input Alarm is already in 'enabled'
mode, any pushes are counted toward triple pushes, which reverses
the enabled state of Zone 2 (see below).
system. To "Disable" the alarm, you must push and hold the
for more than 2.1 seconds. That's why we suggest 3 seconds. If the alarm is already
'disabled,' nothing happens.
When power is applied to the circuit it comes on in 'disabled'
mode and the yellow LED illuminates.
If you enter a zone covered by the alarm, the entry/exit piezo produces a
"beep-beep" and you have about 30 - 40 seconds to disarm the system before the alarm is triggered.
the state of zone 2. This is done by triple-pushing the
button while the alarm is in enabled (green LED) mode. Triple pushing in any
other mode is interpreted as a double click (Enable/Reset) with an
additional extraneous click. The alarm powers-up with zone
1 and 2
The Enable/Reset and Disable command have no effect on the
status of zone 2. The only way to change the state of zone 2 is to
power-off the system (yellow LED) and start from the beginning, or to use this command.
The Alarm Status is displayed on three LEDs.
They are like traffic lights, with Red - Yellow - Green.
Disarmed (okay to walk about freely).
Blinking sequence 1 (Red, Yellow, Green) - Armed, Enabled, and using only
Blinking sequence 2 (Green, Yellow, Red) - Armed, Enabled, and using both
- Armed and alarm has been triggered once.
Armed and alarm has been triggered 2 or more times.
RA0 - Command
input (from a momentary switch)
RA1 - Input
from zone 1 detectors
RA2 - Input
from zone 2 detectors
RB0 - Controls Green LED
RB1 - Controls Yellow LED
RB2 - Controls Red LED
RB3 - Controls
Strobe light - used every time alarm is triggered
RB4 - Controls
Horn/Buzzer - used only when triggered and entering or in red alert
RB5 - Controls
Siren - used only when triggered and entering yellow alert
RB6 - Controls
speech/Warning module - used when triggered and entering yellow alert.
RB7 - Controls
barking dogs module - used every time alarm is triggered
RA3 - Controls
power for amplifier/speakers (used by "Barking Dogs" and verbal warning)
The Strobe light is turned on when the alarm is
triggered and is the last device to be turned off before the system
The Horn is extremely loud (120 decibels) and is used only in the second stage.
It is cycled ON for several seconds and then OFF for about two
seconds. It is cycled so the "barking dogs" module
(also used in the second stage), can be heard.
repeat for about 30 seconds.
The Siren is only used the first time the alarm is triggered. Thereafter, the Horn/Buzzer is used. The pitch of the siren is made
to rise and fall by depressing and releasing a momentary switch on the
Siren's PCB. Solder a lead from the load-side of the momentary
switch to the relay, thereby controlling the wailing of the siren by
setting RB5 high and low. The software varies the times the relay is
on and off, creating a very realistic effect.
The Record/Playback module was bought from RadioShack for about $10. It runs flawlessly at 12 volts. The module has a
momentary switch on the PCB to trigger the playback. Connect a
lead to output 6 of the PIC Lick-1 module. The 2-Input Alarm triggers the playback
by pulsing this lead. The message is a verbal
warning to "leave the premises ..." and is used only the first
time the alarm is triggered, with the siren, strobe and barking dogs.
This is a Velleman's electronic watchdog kit and does an excellent job of
sounding like barking dogs. The module has a momentary switch on
PCB to trigger the barking dogs. Solder a wire from the positive
side of the momentary switch to RB6 on
the PIC LICK-1 board. The alarm triggers the playback by pulsing this
lead LOW. The dogs bark every time the alarm is
I used an old Kenwood KAC-524 car amplifier (60 Watts x 2) and some car speakers for
the verbal warning and barking dogs. The nice thing about car
amplifiers is that they have a built-in power control connection that
is normally connected to the ignition switch and can easily be
controlled by the 2-Input Alarm. The circuit powers the amplifier only when
it is needed and turns it off after use.
The 2-Input Alarm has a delay between the time when an intruder is detected
and the alarm is triggered. This is called the entry-delay and the beeper
on the alarm produces a beep-beep to give the user time to disable the
This is the only
way to give commands to the 2-Input Alarm (enable/reset, disable).
doorbell or any other push-switch can be used. A capacitor
across it helps to produce a clean pulse.
This is an
Ultrasonic Movement Detector (such as Tech Amercia kit 990-0203). It
will detect movement up to 20 feet away.
This is a light-detector - ideal for a cupboard, drawer or
toolbox. Pick a drawer that is not in regular use so the alarm can be active
all the time.
2-Input Alarm MkI
1 - PIC Lick-1 module|
Other components can be
bought from your local electronics store.
Kits for PIC Lick-1 can be obtained from Talking Electronics: