Electronics AS project Essay Example for Free

Electronics AS project Essay The aim of this project is to create a fire alarm which will detect fire or the effects of fire and as a result, with a buzzer, aware any occupants and persons in the surrounding area. To do this, I have researched how to construct this particular circuit. Fire is a major hazard and without the proper warning indications, can lead to devastating consequences. This is a device that can solve this life-threatening problem. A device that relies on the smoke that is produced in the event of a fire. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This causes the resistance of LDR to increase and the voltage at the base of the transistor is pulled high due to which the supply to the COB (chip-on-board) is completed. The sensitivity of the circuit can depend on the distance between bulb. A device that uses a thermistor and an LDR to detect the high temperatures and brightness of a fire. When the temperature reaches high, the resistance of the thermistor decreases dramatically and the voltage travelling across the thermistor is pulled high and is passed into an AND gate. The same thing happens with the LDR but as the brightness increases the resistance drops and the voltage travelling through the LDR is pulled high and is passed into the AND gate; switching on a \buzzer alarm. This is the system that I will investigate and use for my system. Using resistors 100K? and 10K? , a 10:1 ratio was formed to work out the trigger point. With the 5. 5K? as R1 the trigger point was made to be 550? which is need for the circuit to trigger at around 80 C. Resistor R1 forms a voltage divider with the thermistor; the voltage to the non-inverting input being larger than the reference voltage when the thermistor is hot. When the thermistor is in high temperatures, the non-inverting input is greater than the inverting input and so the output of the op-amp saturates at the positive supply voltage, +Vs. The output then goes into the same AND gate. This circuit, therefore, gives a logic 0 output in the dark and logic 1 output in the light.