Monday, September 14, 2009

Sensors. Eyes to the Real World!

Touch, the biggest revolution in mobile these days wouldn't have been possible sensors. Infact anything electronic, interpreting real world would have been impossible without sensors. High speed optical fibre communication, Remote controls, touch screens and hundreds and thousands of equipments hungry for real world data would have always remain hungry! But now when have them, interfacing them is the most important thing now.

There are a number of sensors, sensing diffrent type of events around. Sound, Light, Pressure, Flow, displacement and a lot more. And to detect these events we have components which show certain behaviour in presence of above stated events. It is now upto us what property of what substance under given curcumstance, can be best utilised.

Lets take an example of LDR (The very common sensor). It stands for Light Dependent Resistance. When light falls on this sensor, this reduces its resistance. Now measuring change in resistance is an easy task. The good old Ohms law V=IR! if a constant voltage is applied, the current thrrough this sensor will increase with increase in light falling on it.

This is a simple potenstial divider circuit. R is a normal resistance with nearly of the same resistance as of LDR in dark.
Mathematically, V across R will increase with increase in light by equation.
Or can be simply understood as increase in current will cause the drop across R ro increase as Vr=IR.

Now just tap a wire at this junction, one can interface it with ADC to make this data available digitally. But there is a contraint to it. You can use this circuit to measure the light intesity around you. But please do not use this circuit to measure some distance, by measuring the light of a distant transmitter(source). This output is depend on all the combined light falling on sensor. And a large part is the ambient light, which may vary, any time by any amount.

Well there are many other sensors to talk about. Lets talk about them in coming blogs.

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