Remote Control IR Signals
To understand the Direct TV remote control that we want to receive IR commands from, we need to look at what it is transmitting. Below is an example 'command' sent by the remote control.
The two wave forms show you what the output looks like varying from +0v to +5v. The small ripples that you see on the line throughout the waveform is the 38 KHz carrier frequency.
Decoding The Signl
Now for the real stuff. We've seen an example command sent from the remote control, but what does it
mean and how can the microcontroller make sense of it? First let's take a closer look at the command. Again, here's the signal that is transmitted when the number '2' is
pressed on the remote control:
After looking at this for a minute or two, it's pretty evident there's 5 different signals that can be transmitted in a single command: 3.0 mS / 1.15 mS / 1.1 mS / 0.550 mS / 0.505 mS. The first 3mS is what's known as a 'header' because it is always there no matter what button is pressed on the remote. The rest of the signal is data.
Since we only care about the signal data being transmitted, let's assign the different pulses the following digital decoding values:
1.15 mS -> 11
1.10 mS -> 00
0.550 mS -> 1
0.505 mS -> 0
Now we can create an actual digital value for the data signal. Whether this is actually how Direct TV does their decoding, I don't know and I highly doubt it. No
matter, here's what the decoded value would come about to be:
Now if we decode all transmitted signals like this, each one will have a unique value, and therefore we'll be able to distinguish between the different buttons. But before we can get that far, let's build the thing!
To understand the Direct TV remote control that we want to receive IR commands from, we need to look at what it is transmitting. Below is an example 'command' sent by the remote control.
The two wave forms show you what the output looks like varying from +0v to +5v. The small ripples that you see on the line throughout the waveform is the 38 KHz carrier frequency.
After looking at this for a minute or two, it's pretty evident there's 5 different signals that can be transmitted in a single command: 3.0 mS / 1.15 mS / 1.1 mS / 0.550 mS / 0.505 mS. The first 3mS is what's known as a 'header' because it is always there no matter what button is pressed on the remote. The rest of the signal is data.
Since we only care about the signal data being transmitted, let's assign the different pulses the following digital decoding values:
1.10 mS -> 00
0.550 mS -> 1
0.505 mS -> 0
Now if we decode all transmitted signals like this, each one will have a unique value, and therefore we'll be able to distinguish between the different buttons. But before we can get that far, let's build the thing!