Anyways now m going to write about sensors. To begin with , sensors are eyes of the robot. Bots take action only after they “see” what to do. There are various kinds of sensors that are generally used and uncountable number of sensors that can be used.
1st lemme list the most commonly used sensors.
a) LDR (light dependent resistance)
b) Photodiode
c) Filtered Photodiode +IR pair
d) TSOP 1738 etc + IR pair
e) LM35
f) DS 18S20 (Digital )
g) Ultrasonic Transducer Pair
h) Camera
LDR is one of the easily setup-able sensor used by newbies in robotics.
It senses light and changes its resistance accordingly. It is actually a resistor whose resistance decreases with increasing incident light intensity.
Principle : LDR is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electron enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.
Basic LDR circuits are shown in the diagram below
Below is a circuit diagram where LDR is used track a light source.
The circuit has got 5V on one end of the photocell group and ground on the other end. If the same amount of light fell on both photocells the middle voltage would be 2.5V. In the second stage, we had a comparator that compared the photocell group middle voltage to 2.5V. If the photocell voltage was higher than 2.5V, meaning more light falls on the left photocell, the comparator would output 1 and then in the following step the H-bridge would force the servo to turn to the photocell group to the left, aiming to equalize the amount of incident light falling on both photocells. the open-collector invertor is the 7406 and the buffer is the 7407
Next lets discuss photodiodes. A photodiode is a type of photo detector capable of converting light into either current or voltage, depending upon the mode of operation.
Principle :A photodiode is a PN Junction. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a mobile electron and a positively charged electron hole. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced.
A Photodiode schematic symbol
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