label feeding circuit

Discussion in 'The Projects Forum' started by toolman911965, Oct 6, 2010.

  1. toolman911965

    Thread Starter New Member

    Apr 8, 2010
    Hello all, I have come here before and got some good advice but now am looking at a different way. I am building a label feeding device which has labels of different sizes. Originally I designed and built with pneumatic but am rethinking things. Here is what I need: a simple DC motor that will feed a label. The labes are basically opaque but the backing is translucent. Is there a circuit which would allow a foot pedal to actuate the motor, which would feed the label out and when it got to the next label stop, then feed again when the pedal is pressed. I am thinking a simple photo cell might work, but the label would have to feed all the way through then when the next label comes between the photocell it would stop until the foot pedal is pressed again. I will try to do up an image but think it is fairly explanatory this way. push the pedal, label feeds out and stops when the leading edge of the next label hits the sensor. I studied electronics long ago and barely used it so I am very rusty.

    Thanks all for any help it is much appreciated.:)
  2. wayneh


    Sep 9, 2010
    Any idea if the labels are opaque or translucent to IR instead of the visible light we see? You could build your own IR transmitter/receiver pair but there are lots of pre-made "slots" with both components already in place. I've never see one that wasn't IR, but of course that doesn't mean there aren't any. I think you'll need to do a little tuning to get it to differentiate, since they are normally used for clear-path versus no-path, not blurry-path versus no-path.
  3. John P

    AAC Fanatic!

    Oct 14, 2008
    The first thing I think of is a 74HC74 flipflop. The foot pedal hits "set", and makes the output go high and the motor runs. There's a photocell that's connected to the clock line of the flipflop so that a high level is sent to the pin when light on the cell is blocked. A low-to-high transition here loads the flipflop with the contents of the data-in line, which in this case is always 0.

    The idea is that initially, the operator may tap the pedal and the first label is still passing over the sensor. You want to let the motor run until the leading edge of the NEXT label is seen, so you let the motor run while the label passes (clock input high) and also in the space between labels (clock input low). Only when the leading edge of a second label arrives do you clock the chip, on the low-to-high transition.

    But this is in an ideal world. You probably need to add filtering and level-detecting components, to deal with the fact that the photocell won't show a nice clean transition, and may even have some "chatter" near the edges. So I'd plan on adding a schmitt-trigger circuit with an RC filter in front of it. Not a very expensive or complicated thing.
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    Some of the professional machines work on sensing the thickness. If I recall blue light would be the best to use as far as getting a good contrast if you go that way.