Shop OBEX P1 Docs P2 Docs Learn Events
IR LED flashing frequency circuit needed — Parallax Forums

IR LED flashing frequency circuit needed

dw101sdw101s Posts: 27
edited 2009-08-31 01:58 in General Discussion
I am trying to have my robot detect an object by having the object emit IR light. I took a solar garden stake light and changed the white LED with an IR LED that comes with the BOEbot. I charged the battery, and added a switch to turn off the IR light at night instead of having it on light the device was originally designed for. However, when I turned the IR LED on (yes it is lit, I can see the IR light it emits through the LCD screen on my digital camera, so the IR LED is on and working fine), the IR receivers on the robot did not detect the IR light from the IR LED . cry.gif

I think the problem is that the IR LED is a solid light source and not flashing at or near the 38,500 frequency that the IR receivers are designed to detect at. So my question is how can I get my IR LED to flash at a frequency that the IR receivers can see?

FYI, the battery in the solar garden stake is 1.2V AAA.

Thanks in advance.

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-08-02 03:25
    1) The voltage needed for a white LED is very different from that needed for an IR LED. You need to adjust for that or you'll burn out the LED.

    2) The "IR Remote for the BoeBot" tutorial has a circuit using a 555 timer to product the 38.5KHz carrier needed for the IR detector. Look at page 191. Go to the main Parallax webpage and click on the "Resources" tab. In the list that appears, choose "Downloads", then "Stamps in Class Downloads". You'll see a link for the tutorial.
  • kwinnkwinn Posts: 8,697
    edited 2009-08-02 03:27
    You could do it with a 555 timer but you need more than 1.2V. Simpler to build a circuit using 3 x 1.2V cells and connecting led rather than adapting a garden light.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2009-08-02 12:21
    http://forums.parallax.com/showthread.php?p=721739
  • dw101sdw101s Posts: 27
    edited 2009-08-03 02:52
    Thanks for the advice on the 555 timer. The Stamps in Class and IR info was good. I found a website

    http://www.hobbyprojects.com/calculators/555_timer_frequency_duty_cycle.html

    that has a great calculator for a 555 timer circuit. I found that R1 = 1.38KOhms, R2 = 1.2 KOhms and C=0.01micro farads

    This gave a frequency of 38KHz. I tested it out against the IR Receivers from the BOEbot kit and it was able to "see the light".
  • dw101sdw101s Posts: 27
    edited 2009-08-31 01:58
    I would actually like to correct my last statement. I recently tried to recreate the circuit that I quoted from that link with the values that I stated and I couldnt make it work. However, as Mike pointed out Page 191 of IR with the Boe-Bot has a great 555 timer circuit which allows anyone to have an external object separate from the robot to emit a detectable IR signal, just need an external power source (in my case I used 3 AAA batteries). FYI, the 10Kohm potentiometer needs to be around 1.5Kohms in order to get the 38Khz (please, correct me if I am wrong).
Sign In or Register to comment.