I could provide you with code n design for line follower as well as obstacle detector......
Code is only required if you choose to go the microprocessor route, but there are plenty of circuits that can be built with discrete components that will work just fine for a starter project.
i want to start with simple one
which will be more simple
simple robot which i can control with remote , line following robot , or obstacle detector ???
Controlling a robot with a remote will be the easiest, but would possible teach you the least amount. The only possible learning to be done would be learning a little more about transistors if you build your circuit with an H-bridge to control any motors you may use. If you go a little overboard, the use of servo motors will require a little more knowledge.
The line following / obstacle detecting robot would teach you more in my opinion.
*Note, the LDR you used in your last project would be used for a line following robot. You would face it down, and use an LED to light up the floor. When the LDR is over a strip of black electrical tape the resistance will change and the robot will respond. This method would use a very similar circuit to the one you have already built. You would use 2 or more LDRs, one on each side to determine if the robot fell off the left or right side of the tape
