Gas Sensor

Overview
            A gas detector is a device which detects the presence of  gases within an area, usually as part of a safety system. This type of equipment is used to detect a gas leak and interface with a control system so a process can be automatically shut down.


Gas Sensor

Features

• High sensitivity to LPG, natural gas , town gas
•  Small sensitivity to alcohol, smoke.
•  Fast response .
• Stable and long life
• Simple drive circuit

Applications

• Detection of harmful gases in mines.
• Home safety

Using The Sensor

•  Connect regulated DC power supply of 5 Volts to pin 3 and GND to pin2. 
•  When gas is detected LED is ON or else it is OFF. 
•  The output from pin1 can be given directly to microcontroller for interfacing applications.

Working

       The  MQ-7  gas  sensor  is  shown  as (Configuration  A  or  B),  sensor  composed  by  micro  AL2O3  ceramic  tube,  Tin  Dioxide  (SnO2)  sensitive  layer,  measuring electrode  and  heater  are  fixed  into  a  crust  made  by  plastic  and  stainless  steel  net.  The heater  provides necessary work conditions for work of sensitive components. The enveloped MQ-7 have 6 pin, 4 of them are used to fetch signals, and other 2 are used for providing heating current.

As  shown  in,  standard  measuring  circuit  of   MQ-7 sensitive components consists of 2 parts. one  is  heating  circuit  having  time  control  function  (the  high  voltage  and  the  low  voltage  work   circularly ). The second is the signal output circuit,  it  can  accurately  respond  changes  of  surface  resistance of the sensor.

operation  principle: 
 The surface resistance of the sensor Rs is obtained through effected voltage signal output of the  load resistance RL which series-wound. The relationship between them is described:

                                        Rs\RL = (Vc-VRL) / VRL

below fig shows alterable situation of RL signal output measured by using above circuit output
signal  when  the  sensor  is  shifted  from  clean  air  to  carbon  monoxide  (CO)  ,  output  signal  measurement is made within    one or two complete heating period (2.5 minute from high voltage  to low voltage ). Sensitive layer of MQ-7 gas sensitive components is made of SnO2   with stability, So, it has  excellent long term stability. Its service life can reach 5 years under using condition.

ATMEL Schematic:

ATMEL Code:
For Code Click Here.


ARM Schematic:

ARM Code:
For Code Click Here.


PIC Schematic:

PIC Code:
For Code Click Here.

Triple Axis Magnetometer

Overview

           The HMC5883L utilizes Honeywell’s Anisotropic Magneto resistive (AMR) technology that provides advantages over other magnetic sensor technologies. These anisotropic, directional sensors feature precision in-axis sensitivity and linearity.  These sensors’ solid-state construction with very low cross-axis sensitivity is designed to measure both the direction and  the magnitude of Earth’s magnetic fields, from Milli-Gauss to 8 Gauss. Honeywell’s Magnetic Sensors are among the most sensitive and reliable low field sensors in the industry.

Triple Axis Magnetometer:

Features

•  I2C digital interface
• 3-axis magnetorestive sensors. 
•  Low voltage operations. 
•  Sensors can be used in strong magnetic field environments.

Applications

• Weapon systems positioning. 
•  Heart beat monitors. 
•  Locating objects such as submarines, sunken ships. 
•  Can be deployed in spacecraft. 
• Weather prediction.

Working

           The Honeywell HMC5883L magnetoresistive sensor circuit is a trio of sensors and application specific support circuits to measure magnetic fields. With power supply applied, the sensor converts any incident magnetic field in the sensitive axis directions to a differential voltage output. The magnetoresistive sensors are made of a nickel-iron (Permalloy) thin-film and patterned as a resistive strip element. In the presence of a magnetic field, a change in the bridge resistive elements causes a corresponding change in voltage across the bridge outputs.

MODES OF OPERATION

This device has several operating modes whose primary purpose is power management and is controlled by the Mode Register. This section describes these modes.

 

Continuous-Measurement Mode

During continuous-measurement mode, the device continuously makes measurements, at user selectable rate, and places measured data in data output registers. Data can be re-read from the data output registers if necessary; however, if the master does not ensure that the data register is accessed before the completion of the next measurement, the data output registers are updated with the new measurement. To conserve current between measurements, the device is placed in a state similar to idle mode, but the Mode Register is not changed to Idle Mode. That is, MD[n] bits are unchanged. Settings in the Configuration Register A affect the data output rate (bits DO[n]), the measurement configuration (bits MS[n]), when in continuous-measurement mode. All registers maintain values while in continuous-measurement mode. The I2C bus is enabled for use by other devices on the network in while continuous-measurement mode.

Single-Measurement Mode

This is the default power-up mode. During single-measurement mode, the device makes a single measurement and places the measured data in data output registers. After the measurement is complete and output data registers are updated, the device is placed in idle mode, and the Mode Register is changed to idle mode by setting MD[n] bits. Settings in the configuration register affect the measurement configuration (bits MS[n])when in single-measurement mode. All registers maintain values while in single-measurement mode. The I2C bus is enabled for use by other devices on the network while in single-measurement mode.

Idle Mode

During this mode the device is accessible through the I2C bus, but major sources of power consumption are disabled, such as, but not limited to, the ADC, the amplifier, and the sensor bias current. All registers maintain values while in idle mode. The I2C bus is enabled for use by other devices on the network while in idle mode.

 

 For code and design please Click Here