Need help in IR remote transmitter using PIC24F controller

Discussion in 'Embedded Systems and Microcontrollers' started by namratha_r, Apr 2, 2015.

  1. namratha_r

    Thread Starter New Member

    Jan 27, 2015
    23
    0
    Hi..,

    I need help in how to control the appliances at-least using IR transmitter with pic controller. Have gone through the IR remote Hex codes but clearly not understanding. Right now i have generated 38Khz PWM frequency with 50% duty cycle.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,140
    1,790
    Can you be more specific about which IR coding method you plan to use and what is it that you don't understand?
     
  3. namratha_r

    Thread Starter New Member

    Jan 27, 2015
    23
    0
    Actually from IR learner I learnt IR remote hex value
    Code (Text):
    1. 0000 0070 0000 0032 0080 003E 0011 000D 0011 002E 0011 000E 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0010 000F 0011 000D 0011 000D 0011 000D 0011 002E 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0011 002E 0011 000D 0011 000D 0011 000D 0011 000D 0011 000D 0010 000D 0011 000D 0011 000D 0011 002E 0011 000D 0011 002E 0011 002E 0011 002E 0011 002E 0011 000D 0011 000F 0011 002E 0011 000D 0011 002E 0011 002F 0011 002E 0011 002E 0011 000D 0011 002E 0011 0AB5
    This is the ir hex code learnt (Panasonic power button hex value) . So, keeping constant 38khz carrier frequency am not getting how to vary the time period and calculation for that because for each hex code different period is there. This part is very confusing
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Let's see if this helps:
    upload_2015-4-2_8-43-58.png

    That image is from a Vishay TSOP38xx datasheet. I believe almost any Vishay datasheet will have the same data. View that output as a series of 1's and 0's. Your 38 KHz "carrier" is turned on and off. When it is on for approximately 600 uS, the output drops to zero; when it is off for approximately 600 uS, the output goes high. You get your code of 1's and 0's by changing the periods for which the 38 KHz carrier is on or off.

    That is explained in much more detail here, along with some coding schemes: http://www.vishay.com/docs/80071/dataform.pdf

    One problem that you will encounter is that the on and off periods are not very constant. Thus, some method that looks at the transitions is often used to avoid dependency on that time. The Vishay document linked to above explains that too.

    John
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    In the Vishay document, the section on the NEC code is the one I am most familiar with. They all depend on the ability of the transmitter to turn the 38 kHz. carrier on and off in a predictable way to encode the 1's and 0's. The transmitter and receiver must agree on what the protocol is for modulating the 38 kHz. carrier. In the NEC code, note the usage of redundant complement bytes as a method of error detection and to make the transmission of all messages the same length regardless of the pattern of 1's and 0's.
     
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