Wednesday, May 6, 2009

For you the 1st eyes

ROBOT is something that build to fulfill human needs, to obey ( artificial intelligent robot ) certain rule that have been thought (programmed ) in its brain (microcontroller / microprocessor / BEAM brain) , to do specific repeating process/progress (dull robot).For me , human that create robot are intelligent because they are manipulating those robot to do their job. There are two different dimension of time between the robot and human. Average reaction time for homosapiens mechanically is 215 milliseconds. When entering into the dimension of time domain for robotic responses , the fastest reaction time that I was programmed until now is ~500 nanoseconds which mean 400000 times faster than ordinary human response. Simple arithmetic 8-bit binary can be done in 200 nanoseconds. That why , the solution for a complex problem is only with manipulating semiconductor brain. We(Human) are manipulate them. Realized either you or robot have the highest IQ. Now use your beautiful brain to think!!

For this post , I’m actually want to share the idea and knowledge about electromagnetic wave sensor or in simple way the frequency fall into visible light and it is know as light sensor. Its feels good seeing something you build works as what you want.

First autonomous robot that I ever build known as “Photovore” from BugBot,Junkbot books. Photovore is BEAM family robot and functioning as light seeker . But ,is it enough for you to satisfy something that you build 100%(+2% noise) totally copied from a book? from internet? If not , understanding what is happening inside Photovore system become necessary. Doing something without knowing anything same as wasting your time even it is for your thesis. The brain is only contain a single chip of LM339 Operational Amplifier. The LDR(light dependent resistor) eyes is used as input for the comparator ,the first light sensor that I worked with. LDR is made of high resistance semiconductor. If light falling on the device is of high enough frequency , photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistances.

We as a electric/electronic student should know very well about the operation of operational amplifier in comparator mode. Change in intensity of light at LDR(Photovore eyes) will result changing in resistance through it. From 5V supply, there will be a ratio in dividing 5V in two LDR. If Left LDR have higher intensity of light compared to the Right ,then it will have a lower resistance through it. Using simple theory of voltage divider, the lower resistance will get lower voltage on it. This voltage act as an input for the LM339.Right and left reference is actually is connected to a variable resistor. By adjusting that resistor , right and left reference will change. Reference is a comparing value to the input. Example right reference=2.5V , voltage drop across Left LDR=3V,the output from left system of LM339 will be 0.5V.Right Motor will get 5V-0.5V through 2.2K resistor = 4.5V feed to the right motor. The same thing also happen in the other side. We are manipulating the changing of LDR resistance to make that system works as what we want. At dark point , resistance across LDR can be around 50~100 K.ohm and it can be as higher as 200K.ohm and above .From that only we can think further the used of LDR. It is beautiful.

For the next stage , we will see how LDR works as line sensor and colour sensor. Make sure you really understand the simple “super double basic mayo” function of LDR.

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