Here, we are reverse engineering some remote controls to find out the infrared protocol used in the remote controller. Remote controllers used are attached below as figure.
Remote control 1 (Broadcasting Television remote controller):
Remote control 2 (HITACHI CP-X2530WN Projector remote controller):
- Power supply
- Multimeter
- Oscilloscope
- Kingst LA1002 Logic Analyzer (prefer Sigrok Logic Analyzer)
Why wireless?
Before the wireless technology came out, people were using wired communications to receive and transmit data. There was a lot of constraints and inconveniences, for example, the further the distance between the transmitter and receiver, the longer the wire should be, and also the cost will be higher too, and it will be multiplied up when there is more than 1 communications was going on, also it could be very messy with all the wires flying everywhere. So we have the wireless communications to make people's life easier.
How to communicates
Majority of the wireless communications is using infrared to communicate. It is a simplex type communications, which means the communication channel only send information, is a one-way communication. The transmitter is a infrared LED, receiver will be a sensor module. This module is to convert the raw signal to a clean signal for the protocol to decode it as the figure shows below.
The figure below shows 2 signals, 'IR Detected' is the raw signal, 'IR Receiver' is the signal after modulation by the receiver. So the signal from the Infrared LED is the raw signal, which is the signal 'IR Detect'. The LED will blink, in a frequency range of 34kHz to 40kHz, depends on the protocol used, to produce such signal and transmit to the receiver. Then, the receiver will take in the signal and produce such signal as 'IR Receiver'. Notice the delay there, around 200 us, is because the modulation of the signal needs time to process and output a clean signal, and this is the signal for the decoding process.
Example of the wavefrom taken from here
So the full waveform will be something like below
Reference video from Youtube here
What is NEC protocol <<<<<<< HEAD You maybe wondering how does the infrared transmitter send signals. A high or low signal in infrared communication doesn't represent a logical '1' or '0' respectively. It needs to follow certain formats to determine either is a '1' or '0'. There are many protocols used nowadays, some popular protocols such as RC-4, RC-5, Sony and NEC, are widely used in infrared communications.
In this project here, the remote control 2,NEC HITACHI CP-X2530WN, used NEC protocol as a infrared communication. The waveform above is the signal transmitted using NEX protocol.
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I will be directly working on the board, so a power supply of 3V is needed here. From the figure above, some soldering works is done there for conveniences.