Question

If you are trying to build a robot that can work in a mine. Explain how the photodiode, phototransistor and photocell can be used in this robot as sensor based on their functionality

Answer 1

The devices which you had asked has almost same type of function. In a mining robot there are two main and basic functions using these photo sensors.

1) Obstacle detection

2) Metal detection

Obstacle detection :

For a automated robot (which is not controllable by human) the obstacle should be detected in order move in the right path. These kind of robots are just for inspection of the path and can be done easily with low cost. In this kind of mine robot an IR sensor and a photo sensor are used. The IR sensor generates infra red signals and when they hit a material or obstacle they reflects back and these reflected signal is received by a photo sensor( photo diode or photo transistor or photo cell).

A normal Photo Diode and Photo Cell can be used as IR detector but a normal photo transistor cannot be used as a IR detector,There are IR photo transistor which detects IR rays separately. Based on the required accuracy, power requirements, speed ..etc any of these three sensors can be used.

NOTE: Only IR led is used as a light source because normal light may not be reflected on some materials if the material is reflective then led can be used but IR led is most accurated than the normal LED in this application.

Metal detection:

For this application the different kind of metals are tested first and values should be recorded in the robot. Two light emitters and two photo detectors are used. one IR led and the other is high beam photo led, two photo detectors as per requirement. Different materials reflects in different ways , for example gold reflects highly , iron reflects lightly. based on the reflected amount of light we can match the recorded values and find the metal type. this need a high accuracy devices. the IR led used because some metals may not reflect light at all in such conditions IR is used. detectors also two types one is IR photo transistor used only for IR led and the other is photo cell.

i had less time and i hope i had given the maximum info. thanks for the question.