parts:
U1 555 Timer IC
R1 47 ohm resistor
R2 470 ohm resistor
R3 5k variable resistor
C1 0.0047uf ceramic capacitor
LED1,LED2 Infrared LED's


This circuit oscillates two infrared LED's at 40 khz. To make sure it is transmitting IR light, you can get a little tool from radio shack for about $5. It is a small sheet of plastic about 1" by 3" with a special strip of material, that when exposed to IR light glows (it's actually kinda cool..) A way to check for 40khz IR light is to build a circuit that lights an led when 40khz light is detected. You can get the schematic by clicking here.

I am in need of some help on this one.
I tried putting this circuit together and does not work. The ir leds are emitting light but will not work with 40khz tester. The tester is built on the same board as the Ir Oscillator. The led on the tester glows dimly and the 5k variable resistor(form the 555 timmer) will adjust the led on the ir tester.

Yeah, this is tricky because you can't tell if the IR emitter isn't right, or the IR tester isn't right. I've built both circuits and they work together. Also make sure the LED on the tester isn't in backwards.

-andrew

hi

are there any other way to test the circuit other that the tester? i mean like using the oscilloscope? and what results should it shows?

Sure you can use an oscilloscope :-D
(not everyone has these though.. hehe I have $10,000 flat screen o-scopes at my school tho :-P)

Connect the o-scope probes to pin 3 and ground. You should have a nice little squarewave trace on the o-scope. If your scope has a button that measures period or frequency, click it and see what the circuit is oscillating at.

have fun,
-andrew

Please, pins 8 and 4 are not connected directly to Vcc. How is the chip powered?

Hi !
i test so many time, althought the IR reeive module is active, but the distance is very near...
how to increase the distance? please tell me!
thank you very much

Quote

(Guest @ Mar. 27 2004,21:55):
I am in need of some help on this one.  
I tried putting this circuit together and does not work.   The ir leds are emitting light but will not work with 40khz tester.   The tester is built on the same board as the Ir Oscillator.   The led on the tester glows dimly and the 5k variable resistor(form the 555 timmer) will adjust the led on the ir tester.

If I undestand you correctly, the circuit is operating perfectly... the 5k variable resistor on the 555 circuit controls the frequency of oscillation. So, when you say that "it controls the led on the ir tester", I assume you're actually changing the frequency on the 40KHz oscillator, to around 39KHz or maybe 41KHz, so the IR tester sees a weaker "coupling" on the IR signal (because it's tuned to 40KHz) and indicates this by weakening the led brightness.

I tried this circuit and thought I made it horribly wrong. Luckily for me it worked.... At first all I had was a paper weight.

Try this simple 40KHZ circuit,less power consumption and self starting. Very reliable I ahve used it in many robotics applications

Use a 40KHz Xtal and a 74C14 schmitt trigger:


            _|  2M2   |_|   |
        |               |
        |               |
        |     |\        |
        |     | \       |
        +-----|  O------+--------> Output 40KHz
        |     | /
        |     |/  gate 1 of 74C14
        |
        |
      --+--
       XXX   40KHz Xtal
      --+--
        |
        |
      -----
       ---
        -

By my figuring, this will oscillate at closer to 50kHz with R3=5k. Using a 10k pot (R3=6.71k) gives 40kHz.

For greater accuracy, I would use slightly lower C and higher R values. C=.001 uF and R2=R3=12k works for me and yields 40,000 Hz by the formula f=1.45/(C(R2+2(R3))).

For an online 555 calculator see [freespace.virgin.net]

I would like to use this for a project I'm working except I will be using 12 volts instead of 5volts and I have have 8 infrared leds... can someone help me get all the resistors right?

andrew Wrote:
-------------------------------------------------------
> [www.reconnsworld.com]
> 40khzir.jpg
>
> parts:
> U1 555 Timer IC
> R1 47 ohm resistor
> R2 470 ohm resistor
> R3 5k variable resistor
> C1 0.0047uf ceramic capacitor
> LED1,LED2 Infrared LED's
>
>
> This circuit oscillates two infrared LED's at 40
> khz. To make sure it is transmitting IR light, you
> can get a little tool from radio shack for about
> $5. It is a small sheet of plastic about 1" by 3"
> with a special strip of material, that when
> exposed to IR light glows (it's actually kinda
> cool..) A way to check for 40khz IR light is to
> build a circuit that lights an led when 40khz
> light is detected. You can get the schematic by
> clicking here.



Edited 1 time(s). Last edit at 02/22/2008 11:28PM by Justin9.

hey...

i just wondering why?? the signal wave at output pin 3 is not a square pulse..instead, i got a straight line with some voltage value...
is it sometin to do with the 555 timer??is it damaged??or might be due to any other reasons???...

plz help...help..sigh..hehe

andrew Wrote:

> This circuit oscillates two infrared LED's at 40
> khz.

Feeling like asking a dumb question today (about a 10 years old project no less): what's the use of unmodulated 40kHz IR output? is this for testing of some IR comm or something? I'm looking around for some IR references for a project that needs control with a standard (38kHz?) IR remote. Never dealt with IR before - would this oscillator be of any use for testing (if frequency is adjusted down a bit)?

Cheers!