Kerry Wong writes:
In this post, I will show you yet another thermometer/hygrometer build. But instead of using an LCD or 7 segment display for the output, I decided to go retro, using two “needles” to display the temperature and humidity readings instead. And to make the project more fun, I did not use analog meters for the output but chose to use two servos instead. The temperature humidity sensor I used is SHT21 from Sensirion, the same sensor I used in my temperature logging project before. In that project, the temperature and humidity readings were sent over the network and displayed on my web server (you can see the current readings in my lab here).
A digital thermometer hygrometer with analog displays - [Link]
Calibrated differential pressure sensors will find usage in industry and also in every smart home.
Ventilation, air conditioning (HVAC), or any other applications, where a pressure or a flow of air (gas) is essential, can be precisely regulated only if we know a real pressure/ flow conditions. Monitoring of fans functionality, status of filters, …, even for this purpose are very suitable differential pressure sensors from Swiss company Sensirion with an excellent accuracy and long-term stability.
As SDP sensors are differential, they have 2 nozzles. The base of these sensors is a miniature heating element and two temperature sensors. Difference of pressures will cause a small air flow through a component and it will cause a temperature difference in these built-in sensors. Temperature difference is directly depending on the amount (weight) of air flowing through a sensor and it naturally depends just on a pressure difference. A great advantage against membrane pressure sensors is a long-term high accuracy even at measuring of small pressure and maintaining of accuracy of a “zero point”.
As an air specific weight depends on temperature, measurement based only on a temperature difference of two internal sensors wouldn´t be accurate. That´s why SDP sensors have a built-in temperature compensation and linearization, thus an output of a sensor is directly a value usable for further processing. Resolution of sensors is very high and is user selectable in a range of 9-16 bits. Resulting binary value read-out through I2C interface can be divided by a constant shown in a tab. 2.1 on page 3 of the SDP6xxv1.7 datasheet and we´ll get a resulting value in desired units (Pa, bar, inch).
Universal and price-attractive series is the SDP600 (6xx) series, in which we´ll find types optimized for measurement of pressure (SDP 600/610), mass flow (SDP601/611) and types with a minimal power consumption suitable even for battery-operated devices (SDP606/616). All these types are able to measure “bidirectionally” i.e. positive and even negative values. For applications, where we know, that a pressure difference will be always positive (flow by only one direction), it´s possible to use more price-affordable types SDP 500/510 (in fact even these types measure bidirectionally, but their accuracy is not guaranteed in this range). For the most of applications no additional compensation is necessary, only it can be necessary to multiply a resulting value by a constant for an altitude compensation shown in a table 5.4 on page 6 in the datasheet.
How can be this small sensor used to measure flow of a big amount of air?
Relatively simply. All that is necessary is to make a small orifice in a pipe and this way to create a “resistance” as described in the SDPxxx_Bypass_Configuration application note. In an electronics analogy the differential pressure measurement is similar to measurement of voltage on a resistor, which depends on a current flowing through a resistor. SDP sensors can be used even for measurement of a pressure difference in a given pipe against a surrounding environment, in such a way, that one nozzle of sensor will be left “unconnected”. Naturally, such a configuration can only be used if a small leakage of a measured “gas” (air) is acceptable.
Sensirion SDP sensors measure pressure but even a flow - [Link]
Humidity can be measured by various sensors, but sensors SHT from company Sensirion add many benefits moreover.
To be exact, a word „sensors“ is not a suitable expression in this case. As SHT series sensors contain on one chip humidity and temperature sensor, precise supply, low noise linear amplifier, AD converter and a serial interface, they represent a ready-made “device”. Moreover, they´re calibrated, thus to get an exact value it´s only necessary to read out data through a serial interface. In case of SHT2x series, it´s a standard, easy-to-implement I2C interface.
Sensirion sensors SHT2x series was more in detail introduced to you in our article „New sensors Sensirion will take you only 3x3mm on PCB!”, that´s why we´d like to bring you mainly few tips for simplification of development now.
Area of relative humidity and physics of water vapors is quite ample and into its introduction will initiate you the document Introduction_to_Relative_Humidity. Don´t be scared of many quotations, which you´ll find there – fortunately in common praxis we usually manage it with values of relative humidity and a dew point, which can be found together with code examples in Humidity_at_a_Glance.
As humidity sensors are very often used in residential places for regulation of heating and ventilation, also useful can be information about influence of humidity on a thermal comfort. For a practical usage of sensors it´s also important their placement on a PCB and a good access of air, what is in detail described in the document Sensirion_Humidity_Design_Guide. SHT2x are intended for 3VDC power supply, that´s why when using in 5V applications, you can face a problem of different voltage levels. This can be easily solved for example by a circuit described in the document SHT2x_5V_Supply_Embedding.
The program itself doesn´t need to be developed “from zero”. Examples can be found in the document SHT21_Sample_Code and SHT2x_Electronic_Identification_Code. Detailed information about testing and specification of SHT sensors can also be found in documents Sensirion_Humidity_Sensor_Specification_Statement and Sensirion_Humidity_Testing_Guide.
SHT25 – humidity and temperature precisely in every season – [Link]
Temperature, pressure, humidity, flow – all this you have under control with the Sensirion components, the top quality Swiss producer.
CMOSens technology and other innovative technologies of company Sensirion enabled production of top quality calibrated sensors with a long lifetime. As you may have read in our articles:
- New sensors Sensirion will take you only 3x3mm on PCB!
- Professional humidity and temperature measuring with calibrated sensors Sensirion
- Professional solution for accurate measurement of humidity and temperature
or other. Sensirion sensors in fact aren´t sensors but ready-made solutions with a sensor, preamplifier, AD converter and a communication interface. The result of this concept is high disturbances immunity, high accuracy, saving of components and a simplified development.
Do you develop an application, where you´d use Sensirion components?
As we are an authorized Sensirion distributor, we´re able to provide you with free samples of many Sensirion components, especially RH&T and pressure sensors.
Describe us your industrial project in which you´d like to use a given component and let us know at email@example.com.
Soselectronic supports your development with free samples of Sensirion sensors! - [Link]
The world’s smallest humidity and temperature sensor was introduced at Electronica 2012 by Sensirion, setting new standards for size and power consumption.
The SHTC1 sensor is designed for mobile deices, measuring 2 x 2 x 0.8 mm. Based on the company’s CMOSens Technology, the sensor and signal processing electronics are combined on a single silicon chip.
The devices measure relative humidity over a range of 0 to 100 %RH with a typical accuracy of ±3 %RH. The temperature measuring range is -30 to +100 °C with a typical accuracy of ±0.3 °C. Fully calibrated, the sensor has a digital I²C interface, and is suitable for reflow soldering. This makes it compatible with standard industrial mass production processes for electronic modules. Contact company for pricing and availability.
World’s smallest humidity and temperature sensor - [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]
To be able to quickly test a suitability of a sensor for a given application will appreciate perhaps every designer. For this purpose company Sensirion brings an evaluation USB kit EK-P3.
EK-P3 is usable with digital output pressure sensors of SDP5xx, SDP6xx and SDP7xx series. Kit EK-P3 enables literally within few minutes to test a sensor in a given application and to display measured values by a viewer software, which is available on the Sensirion website. Software allows selecting all available resolutions, absolute or relative timing and also to freely choose a sampling time. Output signal can be displayed as linearized or raw data. It is possible to log and save data (CSV), or to export to Excel format.
Advantages / Features:
- complete USB evaluation kit with a pressure sensor
- applicable to SDP5xx, 6xx and 7xx sensors
- viewer SW displays differential pressure over time
- possibility to store measured data in a CSV format
- export to Excel available
Simplify development of applications with Sensirion pressure sensors - [Link]
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]
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]
Sensirion’s SHT series of humidity sensors provide fully calibrated digital readings for relative humidity and temperature. This tutorial explains how to interface two of these sensors (SHT11 and SHT75) to PIC microcontroller.