This project is about building a microcontroller-based digital room thermometer plus hygrometer that displays temperature and relative humidity on 4 large (1 inch) seven segment LED displays which adjust their brightness level according to the surrounding illumination. It consists of a closed loop system that continuously assesses ambient light condition using an inexpensive light-dependent resistor (LDR) and uses that information to adjust the brightness of the display. An inexpensive DHT11 sensor is used to measure temperature and relative humidity. The microcontroller used in this project is PIC16F688, and it runs at 4 MHz clock generated from its internal source. A separate display driver chip (MAX7219) is used to control and refresh the display data on the seven segment LEDs.
TrH Meter: A DIY indoor thermometer plus hygrometer with adaptive brightness - [Link]
When specifying a reference, keep in mind that initial accuracy, temperature coefficient and long-term stability all play a role in overall accuracy of the finished product. By taking some care in applying the reference, and by avoiding some key pitfalls, the reference’s inherent accuracy can be preserved.
Using and understanding voltage references - [Link]
The MAX31855 performs cold-junction compensation and digitizes the signal from a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The data is output in a signed 14-bit, SPI-compatible, read-only format. This converter resolves temperatures to 0.25°C, allows readings as high as +1800°C and as low as -270°C, and exhibits thermocouple accuracy of ±2°C for temperatures ranging from -200°C to +700°C for K-type thermocouples. For full range accuracies and other thermocouple types, see the Thermal Characteristics specifications in the full data sheet.
MAX31855 – Cold-Junction Compensated Thermocouple-to-Digital Converter - [Link]
Ultra-Accurate Temperature Sensor Offers ±0.5°C (max) Accuracy Over a Wide -40°C to +105°C Range
The MAX31725 temperature sensor accurately measures temperature and provides an overtemperature alarm/interrupt/shutdown output. This device converts the temperature measurements to digital form using a high-resolution, sigma-delta, analog-to-digital converter (ADC). Accuracy is ±0.5°C from -40°C to +105°C. Communication is through an I²C-compatible 2-wire serial interface.
The I²C serial interface accepts standard write byte, read byte, send byte, and receive byte commands to read the temperature data and configure the behavior of the open-drain overtemperature shutdown output.
MAX31725 – ±0.5°C Local Temperature Sensor - [Link]
The MAX44006/MAX44008 integrate six sensors in two products: red, green, blue (RGB) sensors; an ambient light (clear) sensor; a temperature sensor; and an ambient infrared sensor with an I²C interface. These highly integrated optical sensors include a temperature sensor to improve reliability and performance.
The devices compute the light information with six parallel data converters allowing simultaneous light measurement in a very short time. The devices consume only 15µA (MAX44006) and 16µA (MAX44008) separately in RGBC + TEMP + IR mode, and also have the ability to operate from 1.8V/3.3V/5.5V supply voltage rails.
RGB Color, Infrared, and Temperature Sensors - [Link]
Controlling temperature has been a prime objective in various applications including refrigerators, air conditioners, air coolers, heaters, industrial temperature conditioning and so on. Temperature controllers vary in their complexities and algorithms. Some of these use simple control techniques like simple on-off control while others use complex Proportional Integral Derivative (PID) or fuzzy logic algorithms. In this project Shawon Shahryiar discusses about a simple control algorithm and utilize it intelligently unlike analogue controllers. Here are the features of this controller:
- Audio-visual setup for setting temperature limits.
- Fault detection and evasive action.
- Temperature monitoring and display.
- Audio-visual warning.
- System status.
- Settable time frame.
- Data retention with internal EEPROM memory.
Intelligent temperature monitoring and control system using AVR microcontroller - [Link]
DHTxx Sensors @ The Adafruit Learning System:
This tutorial covers the low cost DHT temperature & humidity sensors. These sensors are very basic and slow, but are great for hobbyists who want to do some basic data logging. The DHT sensors are made of two parts, a capacitive humidity sensor and a thermistor. There is also a very basic chip inside that does some analog to digital conversion and spits out a digital signal with the temperature and humidity. The digital signal is fairly easy to read using any microcontroller.
DHTxx Sensors Tutorial - [Link]
raph @ raphnet.net writes:
USBTenki is an electronic project to interface sensors to an USB port for collecting weather related data such as temperature. The firmware supports many different sensors and interfaces. It is up to you to decide what your USBTenki will support.
USBTenki: USB Temperature sensors and more - [Link]
USBTemp provides a thermometer. It is based on the DS18S20 digital thermometers. In addition, the thermometer connects to an USB port – you can read the temperature using a commandline tool. In combination with RRDTool you can easily create temperature graphs
USBTemp – USB temperature measurement - [Link]