Simple Coffee Temperature Indicator Circuit

Ever burnt tongue on coffee that is way too hot?

This post shows how to build a special circuit that tells exactly how hot your coffee is!

It uses a sensor to measure the temperature and lights LEDs to show if it is just right for drinking.

This way one can enjoy coffee at the perfect temperature every time.

Circuit Working:

Parts List:

Why is measuring the coffees temperature important?

The two most important factors that affect coffees flavor are its strength and temperature.

Getting the proper temperature is a little more difficult than figuring out the strength.

The majority of coffee drinkers want their coffee hot at 80 degrees Celsius.

This built-in circuit protects customers from the danger of burning the tongue because not everyone has an inbuilt thermometer in their taste buds.

Two LEDs, a comparator, a temperature to voltage converter and a voltage regulator make up the coffee temperature indicator circuit.

The circuit functions as follows:

The integrated circuits output is logical 0 and transistor T1 does not conduct current if the coffee temperature drops below the specified threshold.

Transistor T2 conducts during this period which flashes the red LED.

On the other hand the green LED flashes when the temperature reaches the desired level.

After calculating the temperature IC2 converts it into a voltage value.

In order to do this IC2 has to be submerged in the coffee or kept within an empty enclosure that can be used as a probe.

As the temperature rises by 10 mV per degree the IC2 output rises accordingly.

Therefore P1 potentiometer is used to adjust the reference temperature at the IC3s negative input to 800 mV if one thinks that coffee tastes best at 80°C.

The comparator output changes to logic 1 enabling transistor T1 to conduct current when the voltage at IC3s plus input reaches 800 mV.

T2 turns off at this moment and the red LED becomes dark.

On the other hand if the green LED turns ON it means that the coffee is at the proper temperature and flavor.

Formula and Calculations:

The exact temperature sensor IC LM35 generates an analog voltage output equal to the temperature in Celsius.

The following methods is used to provide a temperature indicator with the IC LM35:

Basics of the IC LM35:

The LM35 generates a voltage that is exactly proportionate to the Celsius temperature.

Temperature and the IC LM35s output voltage Vout are connected by the following formula:

T_C ​= V_out​​ / 10

where:

• TC is the temperature in celsius.
• V_out is the output voltage of the IC LM35 in millivolts mV.

Example Calculation:

If the LM35 outputs V_out = 500V then the temperature T_C​ would be:

T_C = 500 mV / 10 = 50∘C

How to Build:

To build a Simple Coffee Temperature Indicator Circuit follow the below steps for connections and assembling:

• The 741 operational amplifier IC3 should be connected to the LM35 temperature sensor IC2.
• The datasheets for these components provide pinout details.
• To give the circuit a steady power source connect the voltage regulator IC 78L05.
• Connect the LM35s negative end to ground and its positive end to the power source.
• To adjust the reference temperature for the IC3 741 comparator connect the potentiometer P1.
• The LM35 IC2 temperature sensor should be connected to the 741 IC3.
• When filtering and enhancing use the proper resistors and capacitors.
• To see the current coffee temperature connect the red and green LEDs.
• To control the LED lighting depends on the comparators output than use transistors T1 and T2.
• Following the schematic diagram put the circuit together on a breadboard.
• Verify that all connections are OK and look for any signs of short circuits.
• While keeping the circuit components dry submerge the IC LM35 probe in the coffee or use a probe such as an empty pen.
• Turn the circuit on then look at the LED signs.
• When the coffee temperature falls below a certain point the red LED is expected to light up and when the coffee temperature reaches the desired level the green LED will flash.

Note:

The details may change depending on the exact components and specifications one chooses so keep in mind that this is just a basic tutorial.

To make sure the circuit is operating correctly always check the component datasheets and confirm the connections.

If electronics are unfamiliar think about getting help from someone who knows how to create circuits.

Conclusion:

With a simple coffee temperature indicator circuit a coffee user can inform without depending just on taste whether their coffee has reached the right temperature.

To ensure a consistency in brewing and to get the most taste from the coffee this might be quite helpful.

References:

LM35