One of the most accessible and rewarding projects in DIY electronics is building a simple thermometer. In this article, we will walk through how to design and build a digital thermometer using the EH-90001 temperature sensor. This project is ideal for beginners and intermediate hobbyists who want to learn more about temperature sensing and digital displays.
The EH-90001 is a versatile temperature sensor that operates well in a range of environments, making it an excellent choice for this project. By using basic components like an LED display and some simple wiring, we’ll create a functional, easy-to-understand thermometer.
This project will involve using the EH-90001 temperature sensor to monitor ambient temperature and display the reading on a 7-segment digital display. The thermometer will show temperature readings in Celsius and can be used in various applications, from home monitoring to hobbyist setups.
● EH-90001 Temperature Sensor: This sensor provides an analog output that corresponds to the ambient temperature. It has a linear voltage-temperature relationship, making it suitable for use in simple temperature measurement circuits.
● 7-Segment LED Display: A common way to display numerical data in electronics. We’ll use this display to show the temperature reading.
● Resistors (Various Values): These will be needed for current limiting, voltage division, and ensuring the correct operation of the circuit.
● Capacitors (10µF): Used for noise filtering and stabilizing the signal.
● Power Supply (5V): A basic 5V DC power supply will be used to power the circuit.
● Breadboard and Jumper Wires: For assembling the circuit before final soldering or permanent assembly.
● Transistor (BC547 or similar): To amplify the analog signal from the EH-90001 sensor to a level that is readable by the display.
● Potentiometer (10kΩ): For calibration and adjusting the sensitivity of the sensor.
● Op-Amp (Optional): For buffering and stabilizing the analog signal if needed.
The EH-90001 sensor is an analog temperature sensor, meaning it outputs a voltage that changes linearly with temperature. Typically, the sensor's output voltage increases as the temperature rises. However, this voltage output is usually quite low, so amplification may be required.
To start, we need to identify the sensor's pins: VCC, GND, and Vout (the output voltage). Connect the VCC pin to the positive rail of your breadboard and the GND pin to the ground rail. The Vout pin will carry the voltage that corresponds to the current temperature.
While the sensor may be able to work with a simple voltage divider or low-pass filter, we will also use a small transistor (like the BC547) to amplify the signal. This ensures that the output voltage is high enough to drive the 7-segment display.
The voltage output from the EH-90001 will likely be small, so a transistor can be used to amplify the signal. Connect the Vout pin from the EH-90001 to the base of the transistor through a current-limiting resistor (about 10kΩ).
Next, connect the collector of the transistor to the positive rail of the breadboard (5V). The emitter of the transistor will be connected to the anode (positive side) of the 7-segment display.
This transistor setup ensures that the weak analog signal is amplified enough to control the 7-segment display's current. The transistor will essentially function as a current buffer to drive the display.
A 7-segment display has seven individual segments that can be illuminated to form numbers. To connect the 7-segment display, you need to wire each segment (labeled A through G) to the output pins of the transistor.
However, controlling a 7-segment display directly from the analog output of the EH-90001 is not practical. Instead, we will use the transistor to control a set of digital logic gates that will convert the analog signal into a form that the 7-segment display can interpret.
Using a decoder or a driver IC like the CD4511 BCD to 7-segment decoder will simplify this task. The BCD decoder takes a binary-coded decimal (BCD) input and converts it into a 7-segment display format.
Wire the output from the transistor to the input of the BCD to 7-segment decoder, then connect the decoder’s output to the 7-segment display. You’ll need current-limiting resistors in series with each of the segments to protect the display from excessive current.
To ensure that the temperature reading is accurate, you may want to calibrate the sensor. Insert a 10kΩ potentiometer in the circuit between the output of the EH-90001 and the base of the transistor. By adjusting the potentiometer, you can fine-tune the sensor’s sensitivity to match the actual temperature readings of a reliable thermometer.
The potentiometer essentially allows you to adjust the gain of the circuit, ensuring that the output voltage from the sensor matches the temperature displayed on the 7-segment display. Experiment with turning the potentiometer while measuring the output on a multimeter to match the readings with the expected temperature.
To power the circuit, simply connect a 5V DC power supply to the breadboard. Ensure that the VCC pins of both the sensor and the 7-segment display are connected to the positive rail, and the GND pins are connected to the negative rail. Double-check all connections before turning on the power.
Once the circuit is powered on, the sensor will begin to output a voltage corresponding to the temperature. You should see the 7-segment display light up with a number. If the number displayed is not the actual room temperature, adjust the potentiometer to calibrate the circuit.
For instance, if the room temperature is 22°C, and the display shows 18°C, adjust the potentiometer until the display shows the correct value.
This process might take some time, but once the calibration is done, the thermometer will provide an accurate and reliable temperature reading.
You can expand the functionality of this digital thermometer by adding a simple range switch. If you want to use the thermometer for specific temperature ranges (like measuring from 0°C to 50°C), you can integrate a range selector switch that changes the resistor values in the circuit. This will allow you to shift the output voltage range and effectively measure a wider spectrum of temperatures.
Once you’re happy with the prototype, you can solder the components onto a permanent PCB or use a project enclosure to house the circuit. Ensure that the 7-segment display is clearly visible and that the sensor is positioned where it can accurately measure the temperature.
You could also add extra features like a temperature alert when the temperature exceeds a certain threshold, or even an LED indicator that lights up when the temperature is within a particular range.
By following these steps, you've successfully built a digital thermometer using the EH-90001 temperature sensor, a 7-segment display, and a few supporting components. This project not only introduces you to the workings of temperature sensing but also gives you experience in amplifying analog signals and using a 7-segment display to show the output.
Such projects are a fantastic way to hone your skills and can be extended to a variety of applications, from weather stations to custom control systems. With a little creativity, you can enhance this basic thermometer with additional features like memory, higher precision, or wireless monitoring.
Remember, the key to DIY electronics is experimentation, so don’t be afraid to tweak the design, try out different components, and expand on this project as you learn more!
