Temperature Monitor circuit
The described circuit utilizes a thermistor, which is a type of temperature-sensitive resistor, to detect changes in ambient temperature. The thermistor is connected to an operational amplifier (op-amp) configured as a comparator. When the temperature increases, the resistance of the thermistor decreases, resulting in a change in voltage at the op-amp input. This change in voltage is compared to a reference voltage set by a voltage divider, which includes the 47k resistor.
When the temperature exceeds a predefined threshold, the op-amp output transitions from low to high, activating a relay. The relay serves as a switch that can control a larger load, such as a lamp or an alarm system. In this case, the activation of the relay also completes the circuit for an LED, causing it to light up, thereby providing a visual indication of the temperature increase.
Alternatively, by swapping the positions of the thermistor and the 47k resistor, the circuit can be configured to detect lower temperatures, effectively transforming it into a frost alarm. In this configuration, as the temperature drops, the resistance of the thermistor increases, which will again alter the voltage at the op-amp input. If the temperature falls below a certain threshold, the op-amp output will change state, energizing the relay and illuminating the LED to signal the presence of frost conditions.
This circuit design is versatile and can be applied in various temperature monitoring applications, including HVAC systems, refrigeration units, and environmental monitoring setups. Proper selection of the thermistor type and the reference voltage is crucial for achieving the desired sensitivity and response time for specific applications.Using a thermistor in the position shown makes a heat activated sensor. A change in temperature will alter the output of the opamp and energize the relay and light the LED. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.. 🔗 External reference
Related Circuits
This low noise audio power supply circuit can reduce noise and ripple voltage by 40 dB over the 100 Hz to 20 kHz audio range. In portable applications such as... This low noise audio power supply circuit is designed to...
This is a circuit design for a PWM speed control circuit for DC motor rotation. The circuit features two functions: Forward-Reverse operation and Regenerative Braking. The control is achieved using a MOSFET. The circuit allows for the control of...
Setting circles on an astronomical telescope are used as an aid to point the telescope at a specific object in the sky based on the object's celestial coordinates. However, setting circles can be challenging to use effectively and are...
The circuit consists of a TMP35 temperature transmitter that converts a voltage signal output from the TMP35 into a standard 4 to 20 mA current signal. This configuration is suitable for use in automated instrumentation and industrial temperature control...
The need for a device that can detect and extinguish a fire on its own is long past due. Many house fires originate when someone is either sleeping or not home. With the invention of such a device, people...
A common issue with small flashlights is the limited lifespan of both the batteries and the bulb. For example, a typical incandescent flashlight consumes approximately 2 Watts, while the LED flashlight shown in Fig. 1 consumes only 24 mW....