Using sensor to pause motor at marker

Thread Starter


Joined Nov 5, 2015
I have a motor on a dbdt switch that rotates a scroll of paper continuously. Is there some way I can design it that the paper automatically stops scrolling at predetermined points, and then resumes when the switch is reset. Some combination of sensors? Is it possible to do without arduino?


Joined Dec 18, 2016
Are you comfortable with building this?

I'm making some assumptions here. One, your power for this is something like 5-12v (shown as 12v in schematic). Two, your paper is white and you can draw a black line in the margin where you want the motor to stop. Three, you have the ability to take the output signal (12v=run, 0v=stop) and control your motor with it. (You can't get any power out of that signal so don't load it down with a low resistance or the circuit won't work.)

OP1 is a reflective opto-sensor. The LED part of it projects a beam onto the paper and the phototransistor detects the reflected light. You position it so it is close to and faces the margin where you have drawn your black "stop" lines, and when the black passes in front of the sensor the transistor's collector (C) will go to from zero to 12v and will trigger the cross-coupled nand gate to switch. The reset switch cause it to switch back to the run state.