Microcontroller Based Smoke And Fire Detector Cum Alarm

Microcontroller Based Smoke And Fire Detector Cum Alarm is used to detect Fire and Smoke and give alarm when either of them occurs. This circuit is often used in Industries to detect fire and smoke that may occur at the site of hazardous processes (AT89C51). We have used ATMEL 89C51 microcontroller which has 4 Kbytes of programmable memory.

The AT89C51 provides the following standard features : 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, five vector two-level interrupt architecture, a full duplex serial port, and on-chip oscillator and clock circuitry.   Pin Description VCC Supply voltage (GND Ground). Port 0 Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-impedance inputs. Port 0 may also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming, and outputs the code bytes during program verification. External pull-ups are required during program verification.

Working of the circuit : We have interfaced the LCD to the port 0 and 2. The data is sent on P0 while the control signals for the LCD move on Port 2 pin 0, 1, and 2.

The detail functions of each of the pins are as shown below : Pin no. 18 and 19 are connected to the crystal. The function of crystal is to give pulses to the microcontroller which allows the microcontroller to do various calculations. Pin no. 9 of the microcontroller is connected to +5v through a capacitor of 10uF/50v. This causes the microcontroller to reset at Power ON and to begin execution of program from the first line. (P2.4), (P2.5) are connected to switches S1 and S2 while the other end of switches are connected to Ground. So when a button is pressed the port pins P2.4 and P2.5 get a low depending on which button is pressed and the software inside the microcontroller can take appropriate action. IC 7805 is a voltage regulator IC. It is connected in the input voltage line and limits the voltage to +5v to the circuit. Even if the input voltage goes high up to 14 volts, this IC gives only +5v to the circuit thus preventing any damage. Port 1.0 is connected to the Smoke Circuit and Port 1.1 is connected to fire circuit. The microcontroller receives the logic signal from the smoke / fire circuit when the Smoke or Fire is detected. This logic signal is read by the software and indication is given on Channel 1 or Channel 2. We have used a Hooter on Port 3.0 through a relay which is also activated on detection of smoke / fire. Two keys SW1 and SW2 are connected to the microcontroller port 2.4 and 2.5. These are used to stop the hooter (relay on Port 3.0) for smoke and fire respectively. The LCD will display ‘Channel 1 alarm activated’ when Smoke is detected and ‘Channel 2 alarm activated’ when Fire is detected. In normal case of operation the LCD will display ‘Normal Operation’. The software is written in C language.