why use timer 555

Discussion in 'The Projects Forum' started by L_A_L_I, Dec 11, 2009.

  1. L_A_L_I

    L_A_L_I Thread Starter New Member

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    [​IMG]
    I'm interested with the project above which i found on the internet and I'm going to build it for my college assignment. One thing that i don't understand is why it used the 555 timer for the transmitter? What's the purpose of having the 555 timer in this circuit?
    Will it still work without the 555 timer?
  2. Brother_of_the_wind

    Brother_of_the_wind New Member

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    Its set up to run as an astable multivibrator - I think you need it if you want the lights to blink. What is this circuit trying to accomplish?
  3. beenthere

    beenthere AAC Fanatic!

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    The project might be a challenge without component values.
  4. SgtWookie

    SgtWookie Expert

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    It would have helped if you had included the link to the circuit description, like this:
    http://www.redcircuits.com/Page40.htm

    Circuit operation:
    IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

    Now ask yourself, if you omit the IR transmitter portion of the circuit, where will the receiver get information?
  5. L_A_L_I

    L_A_L_I Thread Starter New Member

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    Sorry bout the lack in my 1st post

    At first I think the designer makes the proximity indicator LED to blink because the blinking transmitter, but with 120Hz frequency I think our eyes can't see the blink

    @SgtWookie> Thanks for the addition

    I mean will the circuit works if I connect the LED & resistor directly to the Voltage source and ground without connecting it to the 555 timer

    Will it affect the output of the circuit?
    If the circuit still works properly, then what's the 555 timer's function since its not a digital circuit...
    Last edited: Dec 11, 2009
  6. SgtWookie

    SgtWookie Expert

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    See C3? That effectively blocks the DC output of IC2A.

    Otherwise, IC2A would just output a voltage corresponding to the ambient light level.

    Since the IR emitter is flashing on and off, those transitions are coupled through C3, which blocks DC levels, yet passes the effects of AC; particularly sharp transitions.

    So, it doesn't matter what the ambient light level is; as it's blocked.

    If the IR emitter were on constantly, it would be blocked too.
  7. L_A_L_I

    L_A_L_I Thread Starter New Member

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    I see
    so that means the timer is very important
    thanks for the answer Sarge:)
  8. Audioguru

    Audioguru New Member

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    The circuit might indicate how close you are to a wall. It also indicates how clean or dirty is the wall because it shows the amount of IR that is reflected off the wall.

    Hanging a tennis ball on a string and stopping when it touches your windshield is better.
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