Proximity Sensors
Proximity
Sensors are available in models using high-frequency oscillation to detect
ferrous and non-ferrous metal objects and in capacitive models to detect
non-metal objects. Models are
available with environment resistance, heat
resistance, resistance to
chemicals, and resistance to
water.
Proximity sensors are
switches or sensing devices that can detect a nearby, specific object without
actual contact. There are three types of proximity sensor: inductive,
capacitive and magnetic. They can be either shielded or unshielded. Typically,
all require close positioning to the object being sensed (about ½ inch or
less). Proximity sensors require almost no maintenance, and most are resistant
to environmental contaminants and conditions.
The maximum distance that this sensor
can detect is defined "nominal range". Some sensors have adjustments
of the nominal range or means to report a graduated detection distance.
Proximity sensors can have a high
reliability and long functional life because of the absence of mechanical parts
and lack of physical contact between sensor and the sensed object.
Sharp GP2D12
Distance Measurement Sensor
This sensor takes a
continuous distance reading and reports the distance as an analog voltage with
a distance range of 10cm (~4") to 80cm (~30"). The interface is
3-wire with power, ground and the output voltage.
Features
- Very Small in size
- Less influence on the colour
of reflected objects, reflectivity
- Analog voltage corresponding
to distance
- Detecting distance of 10 to
80 cm
- External control circuit
unnecessary
- Low cost
-->>Press here for Data sheet link
Infra-Red Proximity Sensor Part 1
This proximity sensor,is easy to build, easy to
calibrate and still,it provides a detection
range of 35 cm
This sensor can be used for most indoor
applications where no important ambient light is present.
The basic idea is to send infra-red light through IR-LEDs, which
is then reflected by any object in front of the sensor .
Then all you have to do is to pick-up the reflected IR light.
-->> Citation: http://www.ikalogic.com/infra-red-proximity-sensor-part-1/
Infra-Red
Proximity Sensor Part 2
This article deals with a more advanced IR proximity sensing
scheme, as compared to the one proposed in the previous
article. It is also more expensive but provides more accurate
results even in sunny outdoor environment.
The Principle of operation
As I said, the main idea behind obstacle detection using IR is to
send Infra-Red (IR) light in a certain direction, and if an object is
present no too far from the sensor, IR will be reflected back and detected by
the sensor. But as you may already know, one of the biggest problems that can
cause the malfunctioning of an IR proximity sensor, is the ambient light and
surrounding sources of IR like the sun and halogen lamps that can cause false
triggering of the sensor.
 |
| figure 1.A |
The
ingenious solution that was developed to avoid this problem, is to send pulses
of IR light at a certain frequency instead of a constant beam, and build a
receiver that would only detect IR pulses of the same exact frequency, cutting
of all pulses of higher or lower frequency.
The kind of device capable of
filtering signals this way is called a bandpass filter. There are a lot of
types of bandpass filters, a whole branch of electricity is dedicated to this
subject. Instead of building a band pass filter, we used a very common IR
receiver Module as the one shown in figure 1.A.
That incorporates a receiver, an amplifier and a very reliable filter that
rejects all the signals that are a couple of kilohertz far from the original
central frequency, all in one single integrated circuit, just as big as a 5V
regulator. The central frequency is fixed by the constructor usually at 40 khz.
Figure 1.B shows in simplified way the composition of the IR receiver and the way it filters all the source of light except the the 40Khz IR signal.
Ultrasonic Sensors
Ultrasonic sensors
use sound waves rather than light, making them ideal for stable detection of
uneven surfaces, liquids, clear objects, and objects in dirty environments.
These sensors work well for applications that require precise measurements
between stationary and moving objects.
Ultrasonic Distance Sensor provides range from
very short (2 Centimeters) to long-range (5 Meters) for applications in
detection and ranging. The sensor provides precise and stable non-contact
distance measurements from about 2 cm to 5 meters with very high
accuracy.
The ultrasonic sensor can easily be interfaced
to microcontrollers where the triggering and measurement can be done using two
I/O pin. The sensor transmits an ultrasonic wave and produces an output pulse
that corresponds to the time required for the burst echo to return to the
sensor. By measuring the echo pulse width, the distance to target can easily be
calculated.
Specifications
- Power supply :5V DC
- Quiescent current : <2mA
- Effectual angle: <15°
- Ranging distance : 2cm – 500 cm
- Resolution : 0.3 cm
Features
- Range: 2 cm to 5 m.
- Accurate and Stable range data
- Data loss in Error zone eliminated
- Modulation at 40 KHz
- Triggered externally by supplying a pulse to
the TRIG pin
- 5V DC Supply voltage and Current - <20mA
- Can communicate with 5 V TTL or 3.3V CMOS
microcontrollers
- Echo pulse: positive TTL pulse, 87 µs minimum
to 30 ms maximum (PWM)
-->> Citation:http://www.sunrom.com/sensors/distance/ultrasonic-distance-sensor-pwm-out?sunid=481fd139a0966b09e95fe2d68784a5ab
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