NTC and PTC Thermistors temperature controlled Fan interfaced
with Arduino Node MCU, ESP32
Thermistors are temperature sensitive semiconductors that exhibit a large change in resistance over a relatively small range of temperature. There are two main types of thermistors, positive temperature coefficient (PTC) and negative temperature coefficient (NTC). NTC thermistors exhibit the characteristic of resistance falling with increasing temperature. These are most commonly used for temperature measurement.
We shall be using resistance dividing network as shown where R2 is NTC thermistor value which keeps varying depending on temperature. R1 is constant resistor of 10k value so at 25 degree Centigrade both resistors are equal at 10k and Analog read or Vout will be 2.5 volts.
Vout = Vin*[R2/(R1+R2)] from this formula since we know all the parameters other than R2 we can quickly find out R2=(Vout*R1) / (Vin-Vout)
The circuit is slightly modified so that we have LM393 comparator output of which is connected Arduino, Node MCU or ESP32.
The SPDT Relay(30A) is a high-quality Single Pole Double Throw Relay (SPDT). The Relay consists of a coil, 1 common terminal, 1 normally closed terminal, and one normally open terminal. When the coil of the relay is at rest (not energized), the common terminal and the normally closed terminal have continuity. When the coil is energized, the common terminal and the normally open terminal have continuity. This relay’s coil is rated up to 5V and the contact is rated up to 30A (@250VAC, 30VDC ). You can use it to control high current devices.
When the temperature goes above the set value Arduino Pin 7 gets change in status and this should be used to pull the Pin 12 High which would trigger the relay which in turn switches the Fan On. Instead of using 230volt Fans we are using 12volt DC Fans as they are safer.
The same way when the temperature goes above the set value the Node MCU Pin GPIO7 gets change in status and this should be used to pull the Pin GPIO12 High which would trigger the relay which in turn switches the Fan on.
The same way when the temperature goes above the set value the ESP32 Pin GPIO7 gets change in status and this should be used to pull the Pin GPIO12 High which would trigger the relay which in turn switches the Fan on.