In the world of DIY electronics, creating devices that bridge the gap between the physical world and digital interfaces is always an exciting challenge. One such project that combines both creativity and practicality is building a Digital Thermometer. With its ability to measure temperature and display it digitally, a thermometer is an essential component in many applications, from home automation systems to weather stations.

In this article, we’ll guide you through building a simple yet functional Digital Thermometer using the AF9591A, a highly integrated temperature sensor designed for digital temperature measurement. We will discuss how to design the circuit, interface with a microcontroller, and display the temperature readings.

What is the AF9591A?

The AF9591A is a precision temperature sensor manufactured by Analog Devices. It offers a digital output in the form of a pulse-width modulation (PWM) signal, which can be easily interfaced with microcontrollers for temperature measurement. The key features of the AF9591A include:

· PWM Output: The temperature is encoded as a PWM signal with a frequency proportional to the temperature.

· High Accuracy: It offers high accuracy (typically ±1°C over a wide temperature range).

· Wide Temperature Range: The AF9591A operates within a temperature range of -40°C to 125°C.

· Low Power Consumption: Ideal for battery-powered devices.

· Digital Interface: Eliminates the need for complex analog-to-digital conversion (ADC), simplifying the design.

· Easy to Use: Requires minimal external components to operate.

The AF9591A is a great choice for DIY electronics because it simplifies temperature measurement by providing a digital signal that is easy to process with a microcontroller or other digital devices.

Components and Tools Needed

To build the Digital Thermometer using the AF9591A, you will need the following components and tools:

Components:

· AF9591A Temperature Sensor

· Microcontroller: Arduino or similar (e.g., ATmega328)

· Resistors: 10kΩ for pull-up on the PWM signal

· Capacitors: 0.1µF for power decoupling

· Display: 7-segment display, LCD, or OLED screen (depending on your preference)

· Power Supply: 5V DC power source (can be USB or battery-powered)

· Breadboard: For prototyping

· Jumper Wires

· Button: For turning the thermometer on/off (optional)

· Enclosure: To house the circuit (optional for finished project)

Tools:

· Soldering Iron and Solder

· Multimeter

· Arduino IDE: For writing and uploading code to the microcontroller

· Oscilloscope (optional, for testing PWM signal)

· Wire Cutters and Strippers

Step 1: Understanding the AF9591A and its PWM Output

The AF9591A generates a PWM signal whose pulse width is directly proportional to the measured temperature. For every degree Celsius increase in temperature, the pulse width of the PWM signal increases by a fixed amount (usually around 1.5ms per °C). The AF9591A outputs this signal on its PWM output pin.

Key Parameters of the PWM Output:

· Frequency: The frequency of the PWM signal is constant.

· Duty Cycle: The duty cycle of the PWM signal changes with the temperature. A higher temperature corresponds to a longer high pulse, while a lower temperature results in a shorter high pulse.

The PWM signal can be read by any digital pin on a microcontroller that can measure the time duration of the high pulse (i.e., pulse width). This is typically done using interrupts or timed loops in the microcontroller code. By converting the pulse width back to a temperature, we can easily display the current temperature on a screen.

Step 2: Wiring the Circuit

To start building your digital thermometer, let's wire up the components.

1. Connect the AF9591A to the Microcontroller

· VCC of the AF9591A connects to 5V on the microcontroller.

· GND of the AF9591A connects to GND on the microcontroller.

· PWM Output of the AF9591A connects to a digital input pin (e.g., pin 2) on the microcontroller (Arduino).

· A 10kΩ pull-up resistor is recommended between the PWM output pin and 5V to ensure a stable signal.

2. Connect the Display

Depending on the type of display you are using (e.g., 7-segment, LCD, OLED), the connections will vary. For example, with an LCD, you’ll need to connect:

· VCC to 5V.

· GND to GND.

· SDA and SCL for I2C communication (if using an I2C LCD).

· RS, RW, E, and the data pins for parallel LCD communication (if using a standard LCD).

3. Power Supply

· If you're using an Arduino, you can power the circuit through the USB or a 5V adapter.

· For a portable solution, use a 5V battery pack (such as a USB power bank or 5V battery pack with a suitable regulator).

Step 3: Writing the Code

The most important part of the digital thermometer project is the code. You need to read the PWM signal from the AF9591A and convert it into a temperature reading. Let’s walk through the code step-by-step for an Arduino-based system.

1. Reading the PWM Signal

To read the PWM signal, we use the pulseIn() function in Arduino. This function measures the width of a pulse in microseconds.