Top 10 passive sensors + their transistor circuits

My goal in this tutorial is to give you a broad understanding of how sensors work. Also, we will not go into the deep details of the physics of electronic components or equivalent models. But we will go into the functionality of the sensors enough to understand how the sensors can be used. In this video, I have reviewed the 10 most common passive sensors and introduced various circuits.I have done a detailed tutorial on these components on my TH-cam channel and you can refer to the videos for each one....
in this VIDEO :
What are passive sensors & how to use them?
What is the difference between NTC and PTC?
Applications of NTC thermistor
Applications of PTC thermistor
What is a NTC thermistor?
What is a PTC thermistor?
How The NTC Circuit Works
How The PTC Circuit Works
Light dependent resistors ( LDR)
How The LDR Circuit Works
Dark Detector LED Circuit
LED light detector circuit
Sensitive Moisture Sensor
Magnetic Dependent Resistor (MDR)
MDR Detector Circuitreed switch sensor
reed switch Circuit
IR Detector Circuit
Infrared sensor
Sound active switch sensor
Sound active switch Circuit
Ultrasonic sensor
Ultrasonic Detector Circuit
Gas sensor
Gas Detector Circuit
the preparation and editing of this tutorial took at least one working week so that you, dear colleague, can learn it in a short period of time. All my experience lies in this video.Please make me happy by commenting and liking the videos. Thanks
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[@jerry27syd]

Pretty clear tutorial!, subscribed!

[@daneshkit]

Thank you

[@user-nz5um2pq6p]

that was perfect❤

[@daneshkit]

Thank U & welcome

[@aronhighgrove4100]

4:10 why two NPN in series?

[@user-nz5um2pq6p]

Not a series
The first transistor is the trigger of the second transistor

[@daneshkit]

hi dear friend
no,two NPN not series.
Q1 is the trigger of transistor Q2
At first, Q2 is turned on by the base resistor, so the relay is active.
When the temperature is low NTC resistance is increased and it will activate the transistor Q1.
So, the base current Q2 is cut off and the relay is deactivated.