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Infrared beacon question

  1. Apr 25, 2013 #1
    Hi there,

    I have built an InfraRed beacon using a 555 timer using a 10K pot to tune the circuit.

    How can I test that it is pulsing at the required 38kHz frequency that I need. I have tried using an oscilloscope, by connecting up the earth and probing one of the legs of the IR LED, but I am not having any success.

    Any help in this matter would be greatly appreciated.

    Kind Regards

  2. jcsd
  3. Apr 25, 2013 #2


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    Connect the oscilloscope to both sides of the LED?
  4. Apr 25, 2013 #3
    Tried that, I only get the voltage, no frequency
  5. Apr 25, 2013 #4


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    ??? You mean the scope trace is DC?
    That means the 555 is not oscillating, I think.
  6. Apr 25, 2013 #5


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    If you adjust the scale to see more than one pulse, you can measure the time between pulses. If you don't have any pulses, the setup (or the oscilloscope settings) is wrong.
  7. Apr 25, 2013 #6
    Thank you Sorphiecentaur, I checked it and that is indeed the case. I was using the standard circuit as shown on the datasheet for a 555, and where there is the voltage divider, I have a 22 Kohm resistor and a 10 Kohm pot and a What I didn't know was that in this circuit, to the pot there should be power and pin 6, this I had, but the floating end I had put to ground. Now it is also pointing to the wiper (pin 6), the little blighter is oscillating. now I have to get it from173 kHz to 38 kHz.
  8. Apr 25, 2013 #7


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    Rob K, If you measure the signal at the IRLED you only can know if that it is present at that point. May I suggest that you go one step further, and determine if the IR pulses are really being transmitted? This would mean an IR receiver at some distance from the transmitter. Now, this may seem obvious, but it is true: If you measure the received pulses you validate that your system is really functioning.
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