Infrared Transmitter

Discussion in 'The Projects Forum' started by whycanot, Aug 2, 2011.

  1. whycanot

    Thread Starter Member

    May 22, 2011
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    I have constructed this circuit, and it is really worked. the potentiometer is used to control the distance of signal transmitted, far or short.
    But I dunno how it's work.
    Any1 can explain for me on:
    1) how the potentiometer can be used to control the distance of signal transmitted by IR LED ?
    2) How NE555 IC is working, how it is used to control the on/off of IR LED ?
    Thanks in advanced .
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    You are lucky it worked. The reset pin should be tied to the supply voltage +.

    The 555 is configured as an astable multivibrator, meaning it gives out constant pulses. The frequency and duty cycle is determined by R3, the potentiometer and C1.

    The capacitor is charged through R3 and the potentiometer, and discharged only through the potentiometer. So if you decrease the resistance of the potentiometer the frequency will increase and vice versa.

    It's also strange that the LED at the output of the 555 doesn't have a series resistor. When the output is HIGH you have essentially the LED and the base-emitter diode in series to GND.
     
  3. whycanot

    Thread Starter Member

    May 22, 2011
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    so u means that the potentiometer is not changing the shooting distance of IR LED but the frequency?
    as i adjust the potentiometer, i need to also alter the distance between transmitter and receiver in order to receive the signal
    can u tell me more about this >< why frequency link wif the distance between trans & receiver
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    It would be better not to have several threads open on your problem...

    You are using a TSOP1756 IR receiver which is trimmed to a certain frequency, 56kHz.

    If you look at it's datasheet http://www.datasheetdir.com/TSOP1756+download you will see in figure 1 that the carrier frequency of the received signal has to be near the center frequency of the internal bandpass (56kHz) otherwise the circuit's responsivity decreases.

    That's why when you adjust the frequency of the 555 in the transmitter circuit you will get different maximum working distances between transmitter and receiver.

    The 555 transmitter freq has to match the IR-receiver frequency. If you want to increase the maximum working distance you have to pass more current through the IR-LED or use several in series or focus the light beam.

    Also, the LED's peak power is at 880nm, the TSOP's peak sensitivity at 950nm... (not the perfet match)
     
  5. whycanot

    Thread Starter Member

    May 22, 2011
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    Sorry, I cant really understand about this part >.<
     
  6. whycanot

    Thread Starter Member

    May 22, 2011
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    Sorry, this is the 1st i use forum ~ i never use forum b4 ~ i strt to use only since this mini project is started =X

    How to see for the 56kHz? I just saw 1.0 in the middle of x-axis and 0.6 in the middle of y-axis @@

    Btw, how about if the transmitter IR LED frequency is also 56kHz? then the working distance can be maximum?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    R1 is shown in parallel with LED1.
    Instead, R1 should be in series with LED1.

    If the supply is 9v, the IR transmitter will have ~ 62mA current going through it when Q1 turns on. That is OK, but they can have up to 200mA current. If you are using a PP3 "transistor" battery, then leave R2 as it is. If you are using a better power supply (like a "wall wart" 9v plug supply or other regulated 9v supply) then you can decrease R2 to 39 Ohms.
     
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  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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  9. whycanot

    Thread Starter Member

    May 22, 2011
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    How to see for the 56kHz? I just saw 1.0 in the middle of x-axis and 0.6 in the middle of y-axis @@

    Btw, how about if the transmitter IR LED frequency is also 56kHz? then the working distance can be maximum?
     
  10. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    It's the relative frequency F/Fo where F is the actual frequency received and Fo is the bandpass filter middle frequency, in your case 56kHz.
    e.g. @ 0.8, i.e. 44.8kHz you will have 20% of max sensitivity.

    Yes.
     
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  11. Audioguru

    New Member

    Dec 20, 2007
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    The maximum range of a TSOP IR receiver is when the 56kHz IR pulses are received in "bursts" as explained in the datasheet. You are not sending bursts of pulses so the automatic-gain-control in the TSOP reduces its sensitivity (because it might be interference from a compact fluorescent light bulb).

    If you want to learn about a TSOP then look in its datasheet.
    If you want to learn about a 555 then also look in its datasheet.

    I re-drew your schematic because its transistor was upside-down and it had ground wires all over the place. I added a wire from pin 4 to the positive supply as shown in the datasheet for the 555.

    The transistor is not needed because the 555 has plenty of current to drive the IR LED and the visible LED, both with their own current-limiting series resistor. Then the LEDs connect to ground.
     
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