Measurement and control of temperature and relative humidity finds applications in numerous areas. These days devices are available which have both temperature and humidity sensors with signal conditioning, ADC, calibration and communication interface all built inside them. The use of such smart sensors greatly simplify the design and reduces the overall cost. We discussed in past about Humidity and temperature measurements with Sensirion’s SHT1x/SHT7x sensors. These sensors are capable of measuring both temperature and relative humidity and provide fully calibrated digital outputs. While SHT1x/SHT7x are very accurate sensors, they are still expensive for hobbyists use. This articles discusses the DHT11 sensor which also provides calibrated digital outputs for temperature and humidity but is relatively lot cheaper than the Sensirion sensors. The DHT11 sensor uses a proprietary 1-wire protocol which we will be exploring here and implementing with the PIC16F628A microcontroller that will receive the temperature and humidity values from the sensor and display them on a 16×2 character LCD.
Measure temperature and humidity using DHT11 sensor and PIC - [Link]
MCP9501/2/3/4 family of devices are temperature switches with ±1°C (typical) accurate factory set output thresholds. These devices are ideal for high power supply systems where an overtemperature protection circuit is needed. These devices do not require external components, consume 25 μA (typical), and the factory set thresholds provide simplicity.
MCP9501 – Temperature Switch with Selectable Hysteresis - [Link]
This is a revised version of my LM35 based digital thermometer project that I posted last year. Although it is one of the simplest projects, it is very popular among newbies who are just starting to learn microcontrollers. There was a little flaw in the original project as pointed by some readers. I was using a 1.2 V reference for A/D conversion with PIC16F688 microcontroller. However, the PIC16F688 datasheet says Vref should be equal to or higher than 2.2 V to ensure 1 LSB accuracy of A/D conversion. Here, I am rewriting the same project but this time I am using a MCP1525 IC to generate a precise 2.5 V reference for A/D conversion. This will improve the accuracy of temperature measurements.
Revised version of LM35 based digital temperature meter - [Link]
Calibrated humidity and temperature sensors Sensirion SHT21, SHT25 and STS21 excel by very small dimensions. Thanks to their miniature size and a very low power consumption, you can use them even in small portable devices.
Sensors SHT21, SHT25 and STS21 with I2C digital output belong to the SHT product line, with the CMOSens technology of swiss company Sensirion. SHT21 and SHT25 measure relative humdity and temperature, STS21 measure only temperature. With a new CMOSens chip, reworked capacitive type humidity sensor and the improved band-gap temperature sensor they feature excellent properties. They have very similar and in some aspects even better properties than SHT1x and SHT7x sensors. Also these sensors belong to high quality CMOS sensors, which contain all elements of the measuring chain on one chip: humidity and temperature sensor, precise supply, low noise linear amplifier, AD converter and interface. Inspite of very compact dimensions also SHT21 and 25 sensors remain resolution of 12 bits for relative humidity and 14 bits for temperature. Temperature sensor STS21 has also a 14 bit resolution and a user can choose by a command the resolution of 14, 13, 12 or 11 bits.
I2C interface enables a very simple communication with a host microcontroller, in a Hold/ No Hold Master mode. Defaultly sensors have the same I2C adress set from production. Upon request it is possible to provide sensors with various adresses from producer. STS21 is fully compatible with SHT2x but it has a different I2C address. This enables to use sensor STS21 in applications where humidity measurment is optional and enables to use the same hardware.
New sensors Sensirion will take you only 3x3mm on PCB! - [Link]
Nest learns from your temperature adjustments, programs itself to keep you comfortable, and guides you to energy savings. You can control the thermostat from anywhere using a smartphone, tablet or laptop, and Nest never stops learning, even as your life and the seasons change.
Meet Nest, the world’s first Learning Thermostat - [Link]
Professor Mark Csele writes:
Presented is a simple temperature alarm which uses a PIC16C84 microcontroller and a 2-line LCD display. The alarm displays current temperature in both Celsius and Fahrenheit degrees and features a 3-key keypad which allows the user to set independent high and low temperature alarm points. The alarm also records the minimum and maximum temperatures encountered.
A PIC-Based Temperature Alarm - [Link]
This project describes an easy and inexpensive way of adding a digital thermometer and data logging feature to a PC. It involves a PIC microcontroller that gets the surrounding temperature information from the Microchip MCP9701 sensor, and sends it to a PC through an USB-UART interface. The USB port of the PC is also used to power the device. The open-source Processing programming platform is used to develop a PC application that displays the temperature in a graphics window on the computer screen. The PC application also records the temperature samples plus date and time stamps on an ASCII file.
Low cost temperature data logger using PIC and Processing - [Link]
s p e x writes… [via]
Dear Adafruit Industries,
I just wanted to let you know how excited I was to get my BMP085 prior to the hurricane reaching northeastern Massachusetts.
I rigged it up and logged samples for about 24 hours, you can see my
jury-rigged Arduino, the sensor, and the data.
Thanks so much for the neat device, the great instructions and the sample Arduino library/code. Setup was a breeze! [pun half-intended]
Keep up the good work!
BMP085 Barometric Pressure – Temperature – Altitude Sensor - [Link]