Simple Coffee Temperature Indicator Circuit

Ever burnt your tongue on coffee that is way too hot?

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

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

This way, you can enjoy your coffee at the perfect temperature every time.

Circuit Working:

Parts List:

Why is it important to gauge the temperature of your coffee?

Well, the flavor of coffee hinges on two crucial factors: its strength and temperature.

While determining the strength is relatively simple ensuring the right temperature is a bit trickier.

Most coffee enthusiasts prefer their coffee hot around 80 degrees Celsius.

Since not everyone possesses an innate thermometer in their taste buds the featured circuit comes in handy, safeguarding you from the risk of scalding your tongue.

Coffee temperature indicator circuit comprises a voltage regulator, a temperature to voltage converter, a comparator and two LEDs.

The circuit operates as follows:

If the coffee temperature falls below the desired level the output from the integrated circuit IC is logical 0, and T1 does not conduct current.

During this phase, Transistor T2 conducts causing the red LED to illuminate.

Conversely, when the temperature reaches the optimal level the green LED lights up.

IC2 gauges the temperature and translates it into a voltage value.

To achieve this, IC2 must be immersed in the coffee or housed within an empty pen which can serve as a probe.

The output of IC2 increases proportionally with the temperature increasing by 10mV per degree.

Consequently, if you believe that the coffees ideal taste is at 80°C, you need to set the reference temperature at the minus input of IC3 to 800 mV using P1.

When the voltage at the plus input of IC3 hits 800 mV the comparator output shifts to logic 1 allowing T1 to conduct current.

At this point, T2 switches off and the red LED goes dark.

Alternatively, if the green LED illuminates it indicates that the coffee has reached the desired temperature and tastes just right.

Formula and Calculations:

An analog voltage output proportionate to the temperature in celsius is produced by the precision temperature sensor IC LM35.

The LM35 may be used to create a temperature indication in the following ways:

Fundamentals of IC LM35:

A voltage that is directly proportional to the Celsius temperature is produced by the LM35.

The following formula links temperature to the output voltage V_out of the IC LM35:

T_C ​= V_out​​ / 10

where:

• TC is the temperature in celsius.
• V_out is the output voltage of the 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:

Building a Coffee temperature indicator circuit involves assembling the necessary components and following a set of steps.

• Connect the LM35 temperature sensor IC2 to the 741 operational amplifier IC3.
• Pinout details can be found in the datasheets for these components.
• Connect the voltage regulator 78L05 to provide a stable power supply for the circuit.
• Connect the positive lead of the LM35 to the power supply and the negative lead to the ground.
• Connect the potentiometer P1 to set the reference temperature for IC3 74 comparator.
• Connect the 741 IC3 to the LM35 IC2 temperature sensor.
• Use appropriate resistors and capacitors for filtering and amplification as needed.
• Connect the LEDs red and green to indicate the status of the coffee temperature.
• Use transistors T1 and T2 to control the LED illumination based on the comparators output.
• Assemble the circuit on a breadboard following the schematic diagram.
• Ensure proper connections and check for any potential short circuits.
• Place the LM35 probe into the coffee or use a probe e.g. an empty pen to immerse the LM35 in the coffee while keeping the circuit components dry.
• Power up the circuit and observe the LED indicators.
• The red LED should light up when the coffee temperature is below the set threshold, and the green LED should light up when the coffee reaches the desired temperature.

Note:

Remember, this is a simplified guide and specific details may vary based on the exact components and specifications you use.

Always refer to the datasheets of the components and double check your connections to ensure the proper functioning of the circuit.

If you are not experienced with electronics, consider seeking assistance from someone with expertise in circuit building.

Conclusion:

By using a Coffee temperature indicator circuit coffee drinkers can visually assess whether their coffee has reached the preferred temperature without relying on taste alone.

This can be particularly useful for ensuring consistency in brewing and achieving the best flavor from the coffee.

References:

LM35