Infrared Paper Sensor how would I do this?

Discussion in 'The Projects Forum' started by ltkenbo, Jun 25, 2010.

  1. ltkenbo

    Thread Starter Active Member

    Sep 11, 2008
    henSo I am an EE student and I like projects a lot. Anyways, I serve and bartend at a restaurant and when I am bar tending, whenever drinks are rung in, we have a printer that prints off a receipt with whatever needs to be made. Anyways, sometimes it's not very obvious when receipts come up so I was wanting to make a sensor that would be able to tell when a receipt was printed and then light up an LED as an indication, my initial idea is this:

    The sensor would have an infrared LED which would sit on top of the printer, when a receipt came up the infrared LED would reflect off the paper and an infrared detector would detect that certain threshold of reflected light and therefore light up and LED.

    I was wondering if you think this would work and how the circuit design would be as far as the infared detector. I would think it would use like an IR phototransistor, but I have not taken electronics class yet (will be this fall) so I don't have much experience with designing semi conductor type circuits. So please let me know what you think.
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    If this is the type of printer with an automatic paper cutter, you could use the signal from that to activate the LED circuit.

    Also, easier that the IR led, would be a microswitch. A paper sensor microswitch from an old printer would be pretty easy to implement. It would be as easy as:

    battery, paper switch, resistor, led.

    Instead of using a battery, you could use a cell phone charger type wall-wart if you wanted, or if you employer didn't mind, you may be able to tap off of the power supply in the printer.
  3. John P

    AAC Fanatic!

    Oct 14, 2008
    I think you can do this. In fact there are reflective LED-phototransistor units available that have the parts focused a few millimeters in front of the device for best reflective performance. The things to watch out for are first, when there's no paper the background mustn't be reflective, and second, the ambient light mustn't be so bright that it overwhelms the LED and makes the sensor think the light is always visible. That's especially a problem if the light is incandescent, or if you have to operate in daylight. Direct sunlight is worst of all.
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    I would say most of the bars out there have mirrors as backdrops, so a reflective solution may not be the best idea. If it faced the mirror, no good, and if it faced the open bar, you could have a problem as well.

    The cutter would be the best idea. A simple pulse detector would do, you could also use the paper advance motor to get your pulse from.

    That could trigger a flip-flop, then a button to reset the light when you tear it.

    The microswitch would offer a simple 3 component solution.
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    I think it would be neat to hack the printer and copy the printout info to scroll across the bottom of the TV screen in the bar. Then guys could check what the hot women were ordering.

    Table 6 white wine spritzer - Table 9 Lime Rickie - Table 2 pitcher of Zombies

  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    John P has good advice. If background light is a problem use a modulated emitter-receiver.
    Look at post by zaidpirwani. Might hack a universal remote controller for modilated emitter, hold down a button & replace batterys with wall wart.
    Last edited: Jun 29, 2010