This circuit is like a tiny detective for heat.
It uses a special material piezo transducer that acts like a mini electricity maker.
When this material gets hot or cold, it squeezes itself a tiny bit and zaps out a little bit of electricity.
The circuit can then measure this electricity to figure out how hot or cold things are around it.
Even though these zaps are super tiny, they are enough for the circuit to sense changes in temperature.
Circuit Working:
Parts List:
| Category | Description | Quantity | Power Rating |
|---|---|---|---|
| Resistors | 10k, 220k | 1 each | 1/4 watt |
| 100Ω | 3 | 1/4 watt | |
| Capacitors | Ceramic 10pF | 1 | – |
| Electrolytic 470µF 25V | 2 | – | |
| Electrolytic 100µF 25V | 2 | – | |
| Semiconductors | IC CA3140 | 1 | – |
| IC UM3561 | 1 | – | |
| Transistor BC547 | 1 | – | |
| Zener Diode 3.1V 400mW | 1 | – | |
| Diode 1N34 | 1 | – | |
| LED Red 5mm 20mA | 1 | – | |
| Piezo Disc | 1 | – | |
| Others | Speaker | 1 | – |
| ON/OFF Switch | 1 | – | |
| Battery 9V | 1 | – |
Here is an ultra sensitive heat sensor designed to monitor high temperatures in electronic devices.
It can be placed inside electronic gadgets that typically generate heat during operation.
The circuit also doubles as a sensitive fire alarm.
This heat sensor utilizes the piezoelectric property to detect heat.
The sensor element is an ordinary piezo disc commonly found in buzzers.
The center of the piezo disc is coated with a layer of piezoelectric material called lead zirconate.
The crystals in this material can disorient and reorient when subjected to mechanical, electrical and heat stress.
The direct piezoelectric property of the piezoelectric crystals allows them to generate electric signals when they disorient and reorient due to stress.
This property is employed here for temperature sensing.
A high gain op amp is used to detect the electrical signals from the piezo disc.
The inverting pin 2 and non inverting pin 3 inputs of the op amp IC CA3140 are connected through capacitor C1 to keep both inputs balanced.
When this balance is achieved the output of IC1 remains low.
However, when the piezo disc experiences heat stress it generates a very small current that disrupts the input balance of IC1 causing its output to switch from low to high.
This high output is used to activate the alarm circuit which is based on the ROM IC UM3561.
UM3561 is a ROM IC used to produce alarm tones such as those of a fire engine, ambulance, machine gun or police siren depending on its pin connection pin 6.
In this setup, it functions as a fire brigade siren with pin 6 left unconnected.
UM3561 is a low power IC that requires 3V, so a zener diode is employed to reduce the 9V supply to 3V.
Resistor R4 220k is crucial for maintaining the oscillating frequency of the ROM IC.
Since the output from IC2 is relatively weak transistor T1 is used to amplify the sound for the speaker.
Capacitors C2 and C3 act as buffers to maintain the voltage level for IC2 for a period even if the output of IC1 returns low.
To install, attach the fine side of the piezo disc to the equipments cabinet close to the heat sink or other heat generating devices.
No adjustments are necessary.
Power 9 to12V DC can be sourced from the equipment itself.
Formula:
The BiMOS op amp is the CA3140.
In other words, it combines the advantages of bipolar transistor and MOSFET technology.
Because of its high input impedance, low input current and fast performance, this adaptable integrated circuit is frequently employed in a wide range of applications.
Basic Op Amp Formula:
Although the CA3140 has unique features, its fundamental working principles are the same as those of other op amps.
The optimal op amp golden rule is among the most basic formulas:
Vout = Aol * (V+ – V-)
where,
- Vout : is the output voltage.
- Aol : the open loop gain, is usually quite large for optimal op amps.
- V+: The input voltage that is not inverting
- V- : is the input voltage that is inverted.
Using the CA3140 in a particular circuit layout will determine the precise formula and computations.
How to Build:
To build a Simple Heat Sensor Circuit using Piezo Transducer follow the below mentioned assembling steps:
Prepare the Piezo Disc:
Coat the middle part of the piezo disc with lead zirconate.
Connect the op amp IC1:
- Short the inverting pin 2 and non inverting pin 3 inputs of the op amp IC CA3140 through capacitor C1.
- Connect the output of the piezo disc to the inputs of the op amp IC.
Connect the ROM IC IC2:
- Connect the output of IC1 to the ROM IC UM3561.
- Configure the ROM IC for the desired alarm tone by connecting pin 3 accordingly.
- Use a zener diode to reduce the power supply voltage to 3V for the ROM IC.
- Connect a resistor R4 to maintain the oscillating frequency of the ROM IC.
Amplify the Sound:
- Use transistor T1 BC547 to amplify the sound for the speaker.
- Connect capacitors C2 and C3 as buffers to maintain the voltage level for IC2.
Final Assembly:
- Glue the fine side of the piezo disc to the equipments cabinet near the heat sink or other heat generating devices.
Power Supply:
- Use a power supply of 9 to12V DC which can be obtained from the equipment itself.
Note:
Ensure to take a proper safety and check the connections are secure and correct before powering on the circuit.
Conclusion:
To conclude, a heat sensor circuit using a piezo transducer is a simple and effective way to detect changes in temperature.
By utilizing the piezoelectric property of certain materials this circuit can convert temperature changes into electrical signals, which can then be processed and used to trigger alarms or other responses.
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