You are boiling hot water. How it alarms when 40 degrees Celsius. You should build the simple temperature detector circuit diagram with a buzzer alarm. It can check a changing of temperature. It is so real easy project.
Also, you can apply them to various temperature detectors. For example
Heat – cold water and many others. Follow imagine yourselves.
How does it work
Figure 1 shows the circuit diagram. In circuit has main components.
- LM335Z is a good temperature sensor IC.
- TL071 is a comparator op-amp
- Alarm with Buzzer.
First of all, R1 limits the current to about 1 mA to IC1(LM335Z).
Figure 1—the temperature detector circuit diagram
Then, VR1 adjusts an output voltage to pin 2 (inverting) of IC2.
While, the R2, VR2, R3 are the reference voltage to the comparator at pin 3 (non-inverting). Both resistors R2 and R3 are a voltage divider. And the VR2 adjusts the voltage or the sensitivity of the temperature detector.
The voltage across VR2 is in a range of about 2.8 to 3.3V. Which it is comparable to the temperature range of about 268 to 337 degrees Kelvin, or -5 To 64 degrees Celsius.
You can set the temperature according to want. Since the temperature sensors IC1 can apply from -40 to +100 degrees Celsius.
For VR3 adjust the offset voltage of the input to IC2 (TL071C). To get the output voltage at pin 6 is 0 volts. When input voltage at pin 2 and pin 3 is the same value.
We come back to see it works.
When IC1 detects a temperature less than the VR1 setting. It makes the input voltage at pin 3 more than the voltage at pin 2.
Thus, the output voltage out of pin 6 to be high, to close about 9 volts. This causes Q1 to switch off and buzzer will sound off.
If the temperature starts into higher than the preset value. The voltage is at pin 2 will be more than at pin3.
Thus, the voltage at pin 6 is lower or around 1.3 volts. This causes Q1 to works and buzzer emit loudly.
How to build this projects
We assemble all components on a universal PCB as Figure 2. Since it is fast and saving our money. Also, you can apply this to design a good PCB layout.
But this a little project, you can do it.
Figure 2—the components layout on the universal PCB.
The component lists
Resistors size ¼W +5%
VR1—10K POT trimmers
VR2—1K POT trimmers.
VR3—100K POT trimmers.
Battery 9V with terminal
The universal PCB
Up to $20 shipping discount on first order now: https://jlcpcb.com/quote