Hi guys, sorry for creating a new thread, I searched here for anything that could help me and I found, but I need more help. I have to do a project that is a line follower robot that need to follow some rules too, so first I need a robot that follows a black line (this part I can do) and in the track (line) will have a mark, when the robot gets this mark, "he" needs to turn around (or go back in the same position) and goes throught the line in the opposite way, so when he gets the mark again, he needs to stop. For this, I cant use microcontroller, or any processor, I need to use flip flops, 555, sensors, buffers, drivers, and a stepper motor, only sequential logic (and of course some combinational). I really dont want anyone to do it for me, Im asking for help, for ideas to do it right, if so Ill be very thankfully to you. Sorry for the english and the low knowledge in the area, Im new on digital electronics. Thank you for any help!

 

I can tell you how a trace cutting machine works and it may help with the concept that could possibly be used or adapted.

If you were not already aware, before CNC controlled plasma or gas cutting machines, it was done by placing a white background drawing whereon the desired cut shape was drafted out in a heavy dark line.
The trace head had a light beam directed at the drawing, a small photo sensitive device in the head was tilted in the centre and oscillated and read the resultant light coming back from the line, so if the reading head was directly over the line, the light received went from light-dark-light and the output was an exact balanced sine wave.
Now if the head wandered off the line slightly, the sine wave became unbalanced or biased in one direction, predominantly pos or neg, so a correction voltage was sent to the servo's to move back over the centre of the line, and so on.
Another servo moved the head forward, or a combination of the two.
This may seem a bit more detailed a system that you had in mind, but some how the robot has to 'see' or detect the line.
You say you have done this part, I would be interested in how you did it?
Max.

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At its core, this is similar to a solar tracker for a photovoltaic array. You need a robot with the ability to steer by electric signals. Without knowing exactly what that is, a basic approach would block out something like this:

A light source shines down on the road. To the left and right of the light are two photo cells. Cell outputs are buffered, conditioned, etc. and combined to produce a signal that varies for turn left/turn right. This signal goes to the robot's steering system. With proper adjustment (!) this will keep the robot centered on the line as it goes forward.

You also have to analyze the photocell signals to detect the "mark". For example, if the line is white and the mark is a thick black line across the white line, then the mark will show up as a sharp decrease in both cell signals at the same time. This tells the robot to turn 180 deg. and sets a FF. The next time the cells detect a mark, that is combined with the FF output to stop the robot.

ak

 

A light source shines down on the road. To the left and right of the light are two photo cells. Cell outputs are buffered, conditioned, etc. and combined to produce a signal that varies for turn left/turn right. This signal goes to the robot's steering system. With proper adjustment (!) this will keep the robot centered on the line as it goes forward.

Basically the same principle as the trace cutter.
Max.