Saturday, July 10, 2010

Hacking Infrared with PIC 16F84A


Send an Infrared signal with PIC 16F84 :

In this post, we 'll learn about transmission of the Infra red signals using PIC16F84. You can use Infra red signal in many projects ( Robots, Touch less counters, Theft alarming .. )

All you need to know to start using Infra Red signals are IR transmitters ( IR LEDs ) and IR receivers ( IR receiver modules ).








The IR LEDs are normal LEDs in the outer shape but they emit IR signals and of course these signals cannot be seen by the human eye. You can though make sure it is working fine by using a digital camera. The digital camera can detect the Infra Red signal and makes them visible to you.

This image shows you how the digital camera in the mobile phone can make you see the IR signal transmitted from a normal IR remote control.





The other difference between visible light LED and IR LED is that in visible light LED, the +ve terminal (Anode) is the longer one. But in IR LED, the +ve terminal (Anode) is the shorter one.



The second thing you need to know is the IR receiver module. It is an IR receiver component connected to a demodulator and amplifier circuit. The function of the demodulation circuit is to demodulate the modulated signal received by the receiver module. This means that this module can receive and understand ONLY modulated signals !!!

YES , that's true. And this is used to differentiate between the IR communication and control signals and IR signal emitted from all the objects around us and from all visible light sources. The demodulator circuit has a Band Pass Filter (BPF) that can detect only signals modulated by a 34kHz carrier signal. Here is a datasheet for TSOP312 Infrared receiver module .



 IR Module
This means that if you want to transmit a signal that can be demodulated as (1), you need to send a continuous signal of 34kHz from your IR transmitter LED.





This is the signal I captured from the Remote Control by the IR receiver




And this is the signal I generated from the PIC 16F84A








The software is very simple this time and written in Assembly Language . All it does it sending pulses to the IR LED at the correct frequency for the correct periods of time. It consists of a 34KHz carrier modulated by the signal of consecutive zeros and ones.


I knew the time coding of the TV remote control by capturing the signal using the IR receiver module to the sound card of the PC . Then I viewed it using a sound editing software to show the exact times for the IR signal.



Here is the link for the Proteus 7 model and software for the project.



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1 comment:

Anonymous said...

can i use it to detect objects ??
where can i get the TSOP31?