adding extra leds to 555

Discussion in 'The Projects Forum' started by shico90, Jul 23, 2010.

  1. shico90

    Thread Starter New Member

    Jul 22, 2010
    7
    0
    hello
    i'm building a IR sensor and now i reached that the transmitter is sending and the receiver is receiver but i want to increase the intensity of the sender beam so i thought about adding about 10 extra IR leds
    here is the ciruit i'm using
    [​IMG]
    note:i'm using 5 V battery, is it better to use 9 V?, and what is better to use a regulator and transformer or an 9 v battery
    thank you
     
  2. schmitt trigger

    Active Member

    Jul 12, 2010
    36
    7
    You could add in parallel with R5, D1 and D2, 4 additional strings of identical diodes and resistors.

    But then, you may run out transistor gain. You may be better by replacing it with a darlington or better still, a p-chan mosfet. And when you do so, a 9 volt source will enhance better the gate than a 5 volt one.

    Also, your 100 uF capacitor may have to be increased to 470uf.
     
  3. shico90

    Thread Starter New Member

    Jul 22, 2010
    7
    0
    can i add another transistors and connect there bases to the pin 3
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    2,535
  5. shico90

    Thread Starter New Member

    Jul 22, 2010
    7
    0
    thank you for your reply but what do you mean by follow exactly?
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    Same voltage, same circuit, they will follow the flashes of the first leg.

    You may have a little problem with that configuration though, R1 is way too low, try 1KΩ instead, and bump R2 to 470Ω. A standard 555 will not quite make it to Vcc, it only reaches 1.3 V of Vcc.

    Your LEDs are probably toast, you have 880ma going through them. 100ma is pushing it hard, as is 50ma.

    Assuming your Vf of each LED is 1.5V, then both of them drop 3V. If you use 9v (as the schematic shows) then 6V/6.8Ω = 0.833A. If the power supply was 5V then (subtracting diode drop) 2V/6.8Ω = 0.294A.

    Since I don't know what your LEDs are rated for I'll assume 0.02A, 9V power supply is 6V/0.02A = 300Ω, and a 5V power supply is 100Ω. The article I linked you too explains these details and more. There are power LEDs out there, but I doubt you are using them.

    You need to find the specs of your LEDs, they will not last a second being over driven as they are. I'll be glad to help you with the design if you want.
     
    Last edited: Jul 23, 2010
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