Phototransistor IR Sensor

Discussion in 'The Projects Forum' started by Paul Gravestock, Jul 12, 2015.

  1. Paul Gravestock

    Thread Starter New Member

    Jul 12, 2015
    4
    0
    Hi Guys,
    So I'm trying to design a simple photo transistor circuit.. I want it to be so that when the photo transistor receives light from the IR LED the visible LED goes on. I've designed the following circuit, any feedback to whether it'll work would be fantastic!
    [​IMG]

    Thanks,
    Paul
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,031
    3,803
    It should. Make sure the ir led is lined up nearly perfectly with the phototransistor. Also, r2 for ir led should be about 100 to 330 ohms. About 330 to 1000 ohms on R1.

    Alignment is key because you only have about 10 degrees of error on most photo-transistors.
     
  3. Paul Gravestock

    Thread Starter New Member

    Jul 12, 2015
    4
    0
    Brilliant, thank you so much!

    You mention that alignment is important, this circuits planned application is for a beer pong table. The IR LED and phototransistor would be set into the table in small holes, with the plastic cups/beer reflecting some of the IR waves back on the sensor. I've ordered some of the components to test this, but realistically I don't know if the reflected fraction will be enough. That said, I was under the impression that the value of R1 determined to some degree the sensitivity of the phototransistor?
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Also, that is a really primitive circuit, so don't expect much in the way of separation from emitter to receiver, or immunity from ambient light (sunlight or incandescent lamps).
     
  5. Paul Gravestock

    Thread Starter New Member

    Jul 12, 2015
    4
    0
    Well the application itself is fairly crude, it'll be used only really in the dark, so there shouldn't be much in the way of interference. I am of course open to idea's to improve it. But I'll admit my electronics knowledge is relatively crude, I did a bit at university, but even then anything more than basic op amp/transistor stuff I found pretty confusing.
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,289
    1,255
    You will probably need a little transistor amplifier.
    Something like this might make things easier.
    http://www.mouser.com/ds/2/427/cny70-279705.pdf
     
  7. Paul Gravestock

    Thread Starter New Member

    Jul 12, 2015
    4
    0
    Right, so I've built the circuit, if my phototransistor is connected in what I thought was the correct way, it takes a lot of direct IR on the phototransistor for the visible LED to be bright. But if I connect it what I thought was the wrong way, the visible LED is lit, but becomes ALOT brighter when the IR led is shining on the phototransistor.

    I'm thinking I may need to get the CNY70 like ronv suggests.
     
Loading...