A fire alarm is the most important device for every household.
By warning you about fire accident early this tiny device can save lives.
This article explains how to build a simple fire alarm circuit on your own.
Smaller spaces that do not need a very complex system such residences, businesses or workshops are perfect for it.
It is a simple and affordable way of protecting yourself and your belongings.
What is a Fire Alarm Circuit:
An electronic system called a fire alarm circuit is made to detect the presence of heat, smoke or flames and alert building or area residents of the danger.
When a fire is detected, people can safely leave and fire alarm device can allow quick action to minimize the damage the fire has caused.
Circuit Working:
Parts List:
| Components | Value | QTY |
| Relay | 9V 400Ω | 1 |
| Transistor | BC117, BC547 | 1, 2 |
| Diode | 1N4007 | 1 |
| Electrolytic Capacitor | 4.7µF 25V, 10µF 25V | 1, 1 |
| Resistor | 100k, 1k | 1, 1 |
| Variable Resistor Preset | 500k | 1 |
The heart of the Simple Fire Alarm Circuit is the use 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 there also rises the leakage voltage.
The circuit is carefully built to take advantage of this events in which a rise in Q1 leakage acts as a trigger for transistor Q2.
Formula 1: Temperature induced Leakage Voltage (Vleakage) in Transistor Q1
Vleakage ∝ Temperature
At the time of a fire outbreak transistor Q2 is activated consequently switching on transistor Q3.
The primary function of transistor Q3 is to control a relay offering the flexibility to activate various warning devices such as lights, bells or horns acting as both audio and visual indicators of a fire emergency.
Safeguarding the Circuit with Formulas:
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.
In reaction to the alarm activation the load is connected to the relay connections specifically the Common (C), Normally Closed (NC) and Normally Open (NO) terminals.
An easy way to change the temperature is to use a soldering iron and a thermometer.
After turning on the circuit place a soldering iron tip at Q1 and a thermometer nearby so one can change the temperature by adjusting R1.
Advantages and Disadvantages:
Advantages:
- Due to its extremely low cost a variety of consumers can benefit from this fire alarm circuit.
- Even someone with little knowledge with electronics can easily assemble it because to its simple design.
- Users are able to modify the alarm trigger temperature to meet their own needs.
- By ensuring that warning devices are activated a relay improves the circuits dependability.
Disadvantages:
The alarm can be turned off before the fire hazard is completely resolved due to the non-latching feature.
How to Build:
Follow these instructions to construct the Simple Fire Alarm Circuit:
- To start consult the circuit schematic to understand the connections and component setup.
- Throughout the building process you will refer to this schematic for help.
- Using the schematic as a guide carefully place the BC117 transistors Q1, Q2, Q3, relay and diode D1 on the circuit board.
- Using the proper connecting wires and the schematic as a guide join the components.
- Make sure the connections are correct and safe.
- As stated in the article use a soldering iron and a thermometer to raise Preset R1 to the correct temperature.
- Attach the circuit to a suitable power source.
- Turn the circuit on and test it to make sure it works as it should.
Conclusion:
Those who enjoy electronics and DIY projects can easily create a easy fire alarm circuit.
This affordable solution offers a reliable fire detection method that works especially well in small areas.
We invite you to test this circuit for your safety needs and our comment area is available for your convenience if you have any questions or need help.
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