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Cold Sensor Circuit

This circuit monitors the temperature level in Air-conditioned rooms, Labs, Cold storage etc. and intimate you whether the low temperature is maintained in the room or not. It gives audio visual indications when the Air-conditioning system or freezing system fails and temperature rises. This prevents the spoilage of stored materials. If the temperature is above the preset level, it gives LED indications first and after Four minutes it gives loud beeps inviting immediate attention.

The circuit uses NTC Thermister as temperature sensor. Its resistance decreases when the temperature in its vicinity increases above one degree or more.IC1 is wired as a voltage comparator with its inverting and non inverting inputs tied to two potential dividers. The non inverting input (pin3) receives a variable voltage from the potential divider comprising the NTC Thermister and VR1. Similarly, the inverting input (pin 2) also receives an adjustable voltage from the potential divider R1 and VR2. Preset VR1 adjusts the voltage level at pin 3 slightly lower than that of pin 2 in the idle state in which the room temperature is below 26 degree. VR2 adjusts the voltage level at pin2 of IC1 slightly higher than that of pin 3.

Cold Sensor Circuit diagram

Errata : Pin 8 of IC CD4060 is ground. It should be connected to negative rail.

Normally IC1 will give Zero volt output since its pin3 gets lower voltage than pin2.This is due to high resistance of Thermister in cold. When the Refrigeration system fails, room temperature rises above 30 degree and the resistance of Thermister decreases. This allows more current to flow into pin 3 and output of IC1 becomes high. This triggers T1 and Yellow LED turns on indicating that the room temperature is rising. If this condition persists, T1 remains conducting and the reset pin 12 of IC2 reach the ground potential and the IC2 starts oscillating. With the given values of C1 and R5, Q8 output becomes high after 2 minutes. This makes the Red LED flashing. If the condition continues, Q9 output becomes high after 4 minutes and buzzer starts beeping. In short, if the refrigeration system is not restarted within 4 minutes buzzer beeps to invite the attention.

NTC Thermister and IC CD4060

19 Comments

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  • sophia

    Can i get a complete report on this project

  • nihad abdullah

    The circuit uses NTC Thermister as temperature sensor. Its resistance decreases when the temperature in its vicinity increases above one degree or more.IC1 is wired as a voltage comparator with its inverting and non inverting inputs tied to two potential dividers. The non inverting input (pin3) receives a variable voltage from the potential divider comprising the NTC Thermister and VR1. Similarly, the inverting input (pin 2) also receives an adjustable voltage from the potential divider R1 and VR2. Preset VR1 adjusts the voltage level at pin 3 slightly lower than that of pin 2 in the idle state in which the room temperature is below 26 degree. VR2 adjusts the voltage level at pin2 of IC1 slightly higher than that of pin 3.

  • nihad abdullah

    This circuit monitors the temperature level in Air-conditioned rooms, Labs, Cold storage etc. and intimate you whether the low temperature is maintained in the room or not. It gives audio visual indications when the Air-conditioning system or freezing system fails and temperature rises. This prevents the spoilage of stored materials. If the temperature is above the preset level, it gives LED indications first and after Four minutes it gives loud beeps inviting immediate attention.

    • nihad abdullah

      This circuit monitors the temperature level in Air-conditioned rooms, Labs, Cold storage etc. and intimate you whether the low temperature is maintained in the room or not. It gives audio visual indications when the Air-conditioning system or freezing system fails and temperature rises. This prevents the spoilage of stored materials. If the temperature is above the preset level, it gives LED indications first and after Four minutes it gives loud beeps inviting immediate attention.

  • Moin

    AOA; Can you provide report of this project to me?

  • job

    sir about the buzzer i was also confuse, if i where going to use a speaker what should be the specification. pls response thank you sir.

  • job

    sir,
    the value of R4 & thermister has letter R, for example the thermister 150R so i was really confuse of this..sir can u explain what is the letter R..pls response

  • Anil

    Sir, I would like to use this ckt for our cold store , our safe temp is 4 c to 6c. we need alarm when the temp higher than 8ct. do you have any ckt to use for the same.

  • ANIL

    Sir, I would like to use this ckt for our cold store , our safe temp is 4 c to 6c. we need alarm when the temp higher than 8ct. What is the temparature difference of this ckt

  • jay

    sir it was working in room temp but once i place the thermistor in an ice to testing it turns off for a while but not consistent. after 10secs it will turn on again. i try to use mylar caps instead of electrolytic, but i dont know the exact value for mylar caps
    pls response

  • jay

    sir i already test in breadboard. once supply the circuit of 9v the yellow is turn on instantly .i test in in a room temp only. and then after a couple of mins the red light is flashing and t he buzzer begun to produce sound. this is the operating state when i test in a room temp???? pls response.

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