How to block off the day light

Discussion in 'General Electronics Chat' started by oookey, Jan 1, 2014.

  1. oookey

    Thread Starter Active Member

    May 24, 2010
    Hi all :p, Happy New Year!

    I want to make a IR receiver by using phototransistor, however if I simply hook up as the circuit shown in the image 1, the photo transistor will ON by the day light or bright light, hence the o/p of the op amp would always hi.

    Is there a simple way to block the unwanted light allowing only the IR signal?

    If I add a capacitor (as hi-pass filter) as shown image 2, will it work? Or a RC-tank is best way out?

  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Use an IR filter (perhaps from an old TV etc remote control).
    IR for remotes is usually pulse modulated at ~38kHz so that steady light (daylight) and other spurious sources can be rejected.
  3. bertus


    Apr 5, 2008

    How is the opamp powered?
    If it is single supply, you could run into trouble.

    Is your IR signal modulated?
    If so, a filter in the modulation frequency will help.

    Here is a page from the EDUCYPEDIA with some circuits that might give you some ideas:

    oookey likes this.
  4. Shagas

    Active Member

    May 13, 2013
    You can try many things .
    1) Make your circuit less sensitive
    2) Make your IR source abit more powerfull
    3) Put an optical filter

    And if all those aren't enough well then you will have to use modulation
  5. sirch2

    Well-Known Member

    Jan 21, 2013
    Like Alex_t said, the usual approach is to modulate the IR, normally at 38lHz.
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    A really simple way to make a IR beam-break detector that operates in bright sunlight over distances of several meters is to get a set of garage door safety beam transmitter and receiver, like these. I recently bought a set at Habitat for Humanity Thrift store for $1. It takes a small external circuit to activate a relay when the beam is broken.

    Here is the circuit.
    Last edited: Jan 1, 2014
  7. ian field

    AAC Fanatic!

    Oct 27, 2012
    A decade or so ago, there were plenty of scrap TVs left out for kerbside collection that had photo diodes with integral moulded IR filter. these days they have a single integrated IR receiver with a 38kHz passband.

    A possible source of IR pass filtered opto sensor is the Dettol no-touch hand cleanser dispenser. They're about £12 in most supermarkets, but one or two discount stores have been offering them 2 for £5 - cheaper than buying a gel refill.

    They also contain a 6V motor, a sub miniature microswitch and a 2A to92 transistor, so at the discount store price you pretty much get your moneys worth.