● Many of us burn our tongue while taking hot tan and coffee.
● So to solve this problem we can use this simple digital thermometer which will let you know the status or temperatures of your coffee before drinking it.
● For measuring the temperature you have to just dip the sensor into your tea or coffee. For that install the sensor inside the empty pen which will serve as a probe for you.
● You can set the temperature according to your requirement from 0 degree to 100 degree Celsius.
Fig. 1: Prototype Of Simple Digital Thermometer Circuit On Breadboard
This digital thermometer circuit is based on two IC namely CA3130 and LM35. LM35 works as a sensor to detect the amount of heat present with few more components.
IC CA3130 is a operational amplifier which combine the advantage of both CMOS and bipolar transistor on a single chip. Operating voltage range varies from 5V to 16V. CA3130 has a advantage that they can be phase compensated with a single external capacitor and have terminals for adjustment of offset voltage. In this you can adjust the reference voltage at inverting and non-inverting pin so that when voltage at inverting pin is more than non-inverting pin it will make the out pin high and vice versa. Pin configuration of CA3130 IC is shown below.
Fig. 2: Pin Diagram Of CA3130 IC
And LM35 is a precision integrated circuit temperature and its output voltage is linearly proportional to centigrade temperature. LM35 detects the surrounding temperature and according to reference value set it will give you the output. When output voltage is multiplied by 100 it will give you the temperature sensed in degrees. So you can easily set your reference voltage. Pin configuration of LM35 IC is shown below.
Fig. 3: Image Of Pin Diagram Of LM35 IC
In this circuit we have set the fix voltage at inverting pin that is at pin 2 of IC2 with the help of VR1 like if you like the temperature of coffee or tea at 70 degree Celsius than set the voltage at pin 2 with the help of VR1 to little less than 0.70 volts. And non-inverting pin 3 of IC2 is connected with the output pin 2 of IC1 through a resistor. Initially we have to do some hit and trial method to set the temperature with the help of variable resistor VR1. VR1 provide a reference voltage that can be set anywhere from 0V to approx. 1V.
In our circuit we have set a 0.69 Volts approx. at pin 2 mean when temperature reaches above 69 degree Celsius output pin 6 goes high and transistor T1 conducts and it will give you an indicator with the help of RED LED that temperature of your tea or coffee is more than the temperature set by you. And when temperature is below 69 degree transistor T2 conducts and GREEN LED will glow, indicate that you tea or coffee is at normal temperature and you can drink.
Filed Under: Electronic Projects