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.

VR=12V*(R/(R+R_LDR))

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.

PCB! What the heck???

This post is especially for the beginners and hobbists. Its a great pain making huge circuits on bread boards and much more keeping them alive on them. Its good though in the start but when, its a matter of circuit with communication or clocks, u need noise free circuits. I remember trying UART for the first time and communicatig with the PC via RS232. It took us 3 days to figure out what went wrong. Our code was correct, written over many times, but still it didn't worked! And i guess the hardware was correct too.We finally decided to make a PCB. And it worked! But then what was wrong???

I would call it the inherit devil in each circuit. The "Noise". The more you keep your circuits open, they catch more noise. Remember each conductor is intelf an antenna. So when when it was on a PCB, following happened.

1. No open or loose wires, which means proper connections.
2. Atleast half of the noise due to wires was suppresses.
3. It was easier to track down faults.
4. Probability of working of project increased many folds.

Its not hard to make your own PCB at home. There are a lot of Free tools available to design PCBs. The idea I'm using here holds good only for single-layer PBCs.

Making a PCB is like developing a photograph. Here's what to do

1. Draw your layout using some PCB designing software (PCB EXPRESS (free of cost), EAGLE(Free for small boards), ULTRA ROUTE or anything that’s worth the money and you can lay your hands on.

2. Get its LASER print out on a cheap glossy sheet (my own method of cost effectiveness).

3. Put it upside down on to the copper plate.

4. Iron it for 3-4 minute.

5. Remove the sheet in one go.

Now you'll have a copper plate with black lines on it. Thats your circuit! Dip this in FeCl3 or H2O2

for 15 minutes. These will replace the copper, which comes in contact with the acid. The left over is your PCB. Yes one more problem though. the holes are still required. Well a small drill should do for you. Enjoy!!