ELECTRONICS - [alarm system] - [page 3/9]
3. SCHEMATIC DESIGN
:: 3.1 Heart of the System: PIC16F84
The core of the alarm system is the PIC 16F84 processor. This processor is set to
run at a frequency of 8.86 MHz. It also has a reset switch, which can be used to
reset the processor in case of a failure. The processor operates at a voltage of
5V. The description of the software inside the PIC is placed on a further page.
The Ra/Rb ports are used for I/O with sensors and siren/codelock/codelock LED/
code lock Buzzer and zone1/zone2/zone3 activation.
:: 3.2 Stable Power Supply
The alarm system requires a stable power supply of 5VDC. This is done by a
7805 regulator (which is cooled). The capacitors and diodes around it make
sure the 7805 is working correctly. (The input of this scheme is a rectified
12 VAC voltage, coming from a transformer).
:: 3.3 Rectifier and backup circuit
The transformer gives an AC output signal of 12V AC (Alternating Current). This signal
must be converted to a DC (Direct current) signal. This is done using a bridge rectifier,
diode D5 - D6 - D7 - D8. The AC input is applied to pin 5 and 6 of connector J1. The backup
battery is applied to pin 7 and 8 of connector J1. (If AC power fails, diode D4 will conduct.
This way, the backup battery can power the system). [D1, D2, D3 and pin 1-4 of J1 are not
necessary). The output of this part is a rectified 12VDC voltage.
:: 3.4 Siren Activation
The siren is turned on and off by the relay S2. If the processor set a logical "1" to the
input of R17, the transistor will start conducting. The relay will close, so the kojak
siren is powered.
:: 3.5 Code lock Interface
All wires from and to the code lock are connected to connector J7. Pen nr 1-2 are used for
the +12V power supply. This is the voltage that the code lock kit K2607 requires, stabilization
is not necessary. Pen nr 2-3 are used to control the buzzer. The buzzer is controlled by
a 5VDC voltage. The buzzer is activated by applying a logical "1" (+5V) to the input of
resistor R16. (PIC doesn't control buzzer directy, because of the limited current a PIC output
can deliver. The transistor T1 is used as switch.) Pen nr 5-6 are used as input. (The relay
inside the code lock connects pen 5-6 to each other when the correct code is formed). R14
is a pull down resistor, to ensure the RB6 input of the PIC is never floating. C9 is used
to prevent noise. Pen 7-8 are used to control the LED. The needed current for the LED,
is directly coming from the PIC.
:: 3.6 Sensor/Zone Activation Input
Connectors J2,J3,J4 are used for the sensor inputs. When a complete zone is closed correctly,
pin 1& 2 of these connectors are connected (sensors uses a NC contact. If someone cuts a wire,
the alarm goes off. For each zone, there is a capacitor to prevent noise, and an opto coupler
to pass information to the PIC. (And to overcome the difference in voltage. I've chosen to
work with 12VDC for the sensors). Connector J5 is used as inputs for the zones. (When a zone
is active, +12VDC is applied to the input for that zone).
:: 3.7 The complete diagram
You can view the complete diagram. It contains
all parts that were described in topic 3.1 - 3.6. Note that diode 9-11 don't have to be
installed. Replace by a wire bridge if not used.
