Simple Heat Sensor Circuit using Piezo Transducer

This Simple Heat Sensor Circuit using Piezo Transducer is like small detective for heat.

It uses special thing called piezo transducer which work like tiny electricity maker.

When it get hot or cold it presses itself little bit and make small electric shock.

The circuit look at this shock to know how much hot or cold it is around.

Even a very small shock is very still enough for circuit to feel temperature change.

Circuit Working:

Parts List:

This is super sensitive heat sensor it is made to watch high heat in electronic things.

We can put it inside devices which become hot while working.

This circuit also works like fire alarm.

It uses piezoelectric effect to feel heat.

Sensor part is normal piezo disc which is same like one inside buzzers.

Middle of piezo disc it have a special piezo material called lead zirconate.

This material have small crystals when it get stress from push, electric or heat crystals move and change shape.

Because of this it make small electric signal when it is hot or under pressure.

This electric signal is used here to find heat.

We use strong op-amp to catch small signal from piezo disc.

Pin 2 (minus) and pin 3 (plus) of op-amp IC CA3140 connect with capacitor C1 to keep both side same.

When both side are same IC output stay low with no signal.

But if piezo disc get hot it make tiny current this break balance in IC and output goes high to give signal.

This high output turn ON the alarm circuit and alarm uses ROM IC UM3561.

UM3561 is small chip that make alarm sounds like fire truck, police, ambulance or gun which is based on pin 6 connection.

Here we have not connected pin 6 so it sound like fire engine.

UM3561 need only 3V power so we have used Zener diode to change 9V into 3V.

Resistor R4 220k is important to be sure ROM chip work at right speed.

Because signal from IC2 is not strong we can use transistor T1 to make sound loud for speaker.

Capacitors C2 and C3 keep voltage steady for IC2 and even when IC1 stop giving signal.

We can use stick piezo disc on metal part of equipment near heat area like heat sink.

No need to set anything we can just give 9V to 12V DC power from same equipment.

Formula:

CA3140 is a BiMOS op-amp.

That means it mixes two things: bipolar transistor and MOSFET.

Because it have very high input resistance and a very low input current and also work fast, people use it in many different circuits.

Simple Op Amp Formula:

Even if CA3140 have special features it still work like normal op-amp.

One important rule which is the golden rule for op-amp is this formula:

Vout = Aol × (V+ – V-)

where:

• Vout is output voltage.
• Aol is open loop gain and this value is very big in good op-amps.
• V+ is input voltage on non-inverting pin.
• V- is input voltage on inverting pin.

When we use CA3140 in some circuit this formula help to understand how it work.

How to Build:

To build a Simple Heat Sensor Circuit using Piezo Transducer follow the below mentioned assembling steps:

Prepare Piezo Disc:

• Put lead zirconate on middle part of piezo disc.

Connect Op Amp IC1:

• Join pin 2 inverting and pin 3 non-inverting of CA3140 using capacitor C1.
• Connect output of piezo disc to input pins of op-amp IC.

Connect ROM IC (IC2):

• Take output from IC1 and connect to UM3561 ROM IC.
• Set alarm sound by connecting pin 3 the right way.

Power Supply:

• Use Zener diode to drop voltage to 3V for UM3561.
• Connect resistor R4 to control ROM IC sound speed.

Make Sound Loud:

• Use BC547 transistor T1 to make speaker sound louder.
• Add capacitors C2 and C3 to keep voltage steady for IC2.

Final Setup:

• Stick the thin side of piezo disc on metal body of machine, near heat sink or hot part.

Power ON:

• Give 9 to 12V DC power where we can take this power from the same machine.

Important:

• Be safe before giving power and check all wire and parts are in right place and tigh

Conclusion:

To conclude this Simple Heat Sensor Circuit using Piezo Transducer is easy and works good to find temperature change.

It uses piezoelectric property of special material to turn heat change into small electric signal.

This signal can connect with a alarm or other system to give warning or action.

References:

Piezoelectric sensor

Datasheet IC CA3140

Datasheet IC UM3561