Every home needs a fire alarm!
It is a small device that can save lives by letting you know about a fire early.
This article shows you how to build a basic fire alarm circuit yourself.
It is perfect for smaller places like homes, offices or workshops that do not need a super complex system.
It is an easy and affordable way to keep yourself and your stuff safe.
What is a Fire Alarm Circuit:
A fire alarm circuit is an electronic system designed to detect the presence of smoke, heat or flames and provide an alert or alarm signal to occupants of a building or area.
Fire alarm systems are crucial for early detection of fires allowing people to evacuate safely and providing a prompt response to mitigate the damage caused by the fire.
Circuit Description
Materials Needed:
| S.no | Components | Value | QTY |
| 1 | Relay | 9V 400Ω | 1 |
| 2 | Transistor | BC117, BC547 | 1, 2 |
| 3 | Diode | 1N4007 | 1 |
| 4 | Electrolytic Capacitor | 4.7µF/25V, 10µF/25V | 1, 1 |
| 5 | Resistor | 100k, 1k | 1, 1 |
| 6 | Variable Resistor | 500K | 1 |
The heart of the Simple Fire Alarm Circuit is the utilization of a BC117 transistor Q1 as the fire sensor.
The critical aspect lies in the relationship between temperature and the leakage voltage of the transistor.
As the temperature rises, so does the leakage voltage.
The circuit is meticulously designed to exploit this phenomenon whereby an increase in the leakage of Q1 serves as the trigger for transistor Q2.
Formula 1: Temperature induced Leakage Voltage (Vleakage) in Transistor Q1
Vleakage ∝ Temperature
In the event of a fire outbreak transistor Q2 is activated consequently switching on transistor Q3.
The primary function of transistor Q3 is to actuate a relay offering the flexibility to activate various warning devices such as lights, bells or horns, serving as visual and auditory indicators of a fire emergency.
Safeguarding the Circuit
To protect the circuit from the potentially damaging back electromotive force EMF generated when the relay switches a diode D1 is judiciously employed.
Diode D1 functions as a free wheeling diode, ensuring the circuits longevity and reliability.
Formula 2: Back EMF Suppression using Diode D1
VbackEMF = −L * di / dt
here:
- VbackEMF is the back electromotive force.
- L represents the inductance of the relay coil.
- di/dt denotes the rate of change of current.
Temperature Adjustment and Operation
The Simple Fire Alarm Circuit permits temperature adjustment through Preset R1.
This adjustment feature allows users to set the alarm to trigger at a specific temperature level.
It is important to note that this fire alarm is not latching meaning that the alarm will cease once the temperature in the sensors vicinity falls below the preset threshold.
Formula 3: Temperature Adjustment Using Preset R1
Temperatureset = R1resistance / R1totalresistance*Temperaturemax
where:
- Temperatureset is the set alarm trigger temperature.
- R1resistance is the resistance of Preset R1.
- R1totalresistance is the total resistance of Preset R1.
- Temperaturemax is the maximum allowable temperature.
The connection of the load based on the alarms activation, can be accomplished via the relays contacts specifically the Common (C), Normally Closed (NC), and Normally Open (NO) terminals.
Adjusting the temperature level is a basic process that involves using a soldering iron and a thermometer.
By powering on the circuit and situating the soldering iron tip in proximity to Q1 while concurrently placing the thermometer nearby one can fine tune the temperature setting by manipulating R1.
Advantages and Disadvantages:
Advantages:
This fire alarm circuit is highly budget friendly making it accessible to a wide range of users.
Its uncomplicated design facilitates easy assembly even for those with limited electronics experience.
Users have the flexibility to set the alarm trigger temperature according to their specific requirements.
The inclusion of a relay ensures the activation of warning devices enhancing the circuits reliability.
Disadvantages:
The non latching feature may result in the alarm deactivating before the fire hazard is fully addressed.
Construction Procedure: Building the Simple Fire Alarm Circuit
Follow these instructions to construct the Simple Fire Alarm Circuit:
- Begin by referencing the circuit schematic to understand the component placement and connections.
- This schematic will serve as your guide throughout the construction process.
- Carefully position the BC117 transistor Q1, Q2, Q3, relay and diode D1 on the circuit board according to the schematic.
- Connect the components using appropriate connecting wires following the schematic.
- Ensure that the connections are secure and accurate.
- Adjust Preset R1 to the desired temperature level by using a soldering iron and a thermometer, as described in the article.
- Connect the circuit to a suitable power supply.
- Power on the circuit and conduct tests to ensure it functions as intended.
- Observe the activation of the alarm when the temperature reaches the set threshold.
Final Words: Building a Simple Fire Alarm Circuit
In conclusion, the creation of a basic fire alarm circuit is well within the grasp of electronics enthusiasts and DIY enthusiasts.
This cost effective solution provides an effective means of fire detection particularly suitable for smaller settings.
We encourage you to try this circuit for your safety needs, and should you have any queries or require assistance our comment section is open for your convenience.