phototransistors? photodiodes?

Discussion in 'General Electronics Chat' started by Macabra, Jun 29, 2008.

  1. Macabra

    Thread Starter Active Member

    May 31, 2008
    Attached is the circuit that I want to put together. It is a photoelectric fire alarm circuit. My question is in regards to the transistor Q1. Would that be a common transistor like a IN2222? or a phototransistor? and does it matter which one to use in this case..because I've noticed that some components include a transistor with an LED in them. Additionally, on the DETECT pin, the photodiode, the data sheet said that an LED with low capacitance and low dark leakage current should be used. What is "dark leakage current"?

    Can any please suggest components I could use?

    Much thanks to all.
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Q1 can be any small general purpose NPN transistor. Dark leakage current is the small current the photodiode produces when not exposed to light.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    To save confusion at Radio Shack, that is a 2N2222. All 1N devices are diodes.
  4. Macabra

    Thread Starter Active Member

    May 31, 2008
    Thank you both! =)