Need help in constructing ir circuit project

Discussion in 'Homework Help' started by md.nahid, Jun 23, 2008.

  1. md.nahid

    Thread Starter New Member

    Apr 26, 2008
    Two main part of this project

    1. IR source circuit (Ir Remote)
    2. Receiver

    The receiver circuit has 3 parts:

    1. IR sensor -> input -> 2. opamp 741 -> Output -> 3.MOSFET (Will use as a switch)

    It should work at least 3 meter distant.

    Opamp 741 is in simple non-inverting configuration (Vout = Vi*(1+R2/R1))
    I used R2(feedback) 10M and R1=1M.

    The output of 741 will be used as the gate voltage of MOSFET. So when I send ir signal there will be a input for opamp741 that will amplify the voltage and the amplified voltage used at the gate of MOSFET. Then the LED situated between drain and source will be illuminated.

    The problem is when I contruct the 1st, 2nd and the part separately it is working but not when I join them.

    Anonther problem is that the ir is not working from more than two feet also not working if the source and the reciever are not directional. I need to make them work like TV Remote and from at least 3 meter.

    I'm new in practical circuit project. Please help me in this circuit project with diagram indetails.
    Last edited: Jun 24, 2008
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    We know nothing about your circuits. can you post the schematics?
  3. md.nahid

    Thread Starter New Member

    Apr 26, 2008
    I have added the circuit diagram. Please help
  4. Audioguru


    Dec 20, 2007
    What type of IR sensor do you have? Is it a photo-diode or a photo-transistor?
    It looks like the opamp is not biased correctly.

    Your IR source has a very low current which is the 3v battery minus the 1.4V IR LED voltage which results in only 1.6mA. The LED in a TV remote uses pulses at about 100mA. Decrease the value of the 1k current-limiting resistor until the IR LED operates close to its max allowed current and the range will be much farther.
  5. md.nahid

    Thread Starter New Member

    Apr 26, 2008
    It is a photo diode ir sensor.

    Help me in fixing opamp biasing correctly
  6. m.majid

    AAC Fanatic!

    May 28, 2008
    1k ohm res in source causes very low current to LED,
    reduce res down to 20 ohm,

    why don't you use photo transistor?
    it is very simple to use,

    I suggest you skip op-amp (and no need for -9v)
    connect COLLECTOR of photo-transistor to +9
    connect EMITTER of photo-transistor to GATE of mosfet
    and pull down the GATE with 10k ohm
  7. md.nahid

    Thread Starter New Member

    Apr 26, 2008
    Ok, now I'm using 20ohm.

    The problem is that I have to use opamp and photo diode
    (I'm said to do so, this is the project given).
  8. m.majid

    AAC Fanatic!

    May 28, 2008
    the op-amp circuit seems to be wrong,

    photo-diode generates -10mV~+10mV in various ir lights
    so in your circuit the input voltage (Vi) is about +3V±10mV

    u used op-amp as "Non-Inverting DC Gain"
    u said R2=10M & R1=1M so the gain is 11,
    (Vo = Vi * (1 + R2/R1) = Vi * 11)

    then Vo would be 2.990v*11 ~ 3.10v*11
    then the Vo is always max (near 9 v) and mosfet is always ON.

    i found different circuits for using photo-diode with op-amp try these:
    (see Figure 2-4 (b) on page 6)
    (see "Photo Voltaic-Cell Amplifier" on page 13)