SONY SIRC Protocol Decoding

In this article, we will understand SONY SIRC Protocol, and we will decode this protocol. Afterward, we’ll find out the command and address. Only after getting a clear idea, you can make your own decoder yourself. In this article, we are getting an idea only, and in the next article, we’ll use it to do something. So, let’s start our SONY SIRC Protocol Decoding.

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About SONY SIRC Protocol:

There are three types of SIRC protocol, 12, 15, and 20bit types. All these types have a command and device word. The 20-bit version has only 8bit extended words. Within the bitstream, each word is sent LSB first like this pattern below:

The frame timing is based on multiples of a 600µS pulse with width T. Frames begin with a 4T start mark pulse. Each bit in the frame is represented by a 1T space followed by either a 1T mark (if the bit is 0) or a 2T mark (if the bit is 1). The frame timing is given below:

This pattern is repeated at an interval of 45ms. When a button is pressed in the SONY remote, it repeats each frame at least 3 times.

Modulation:

We have seen the protocol pattern and timing frame. But this signal can not be transmitted so far without modulation. That is why all the IR remotes use modulation in around 36KH ~ 40KHz. SONY SIRC is modulated around 38~40KHz.

Modulation is a mix of one carrier signal and a data signal like this:

SONY SIRC uses a 38~40KHz carrier signal and then the data according to the pattern of this protocol is combined with this carrier signal. An IR LED works as the transmitter.

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The modulated signal for SIRC protocol:

In this way, the command and address are sent through the IR transmitter (IR LED). As modulation is used, a single battery can last a long time and a long distance can be achieved.

Example commands:

The table below shows the commands and addresses of different SONY SIRC Remotes:

Device	Address	Function	Command
TV	1	Digit 0	9
VCR1	2	Digit 1	0
VCR2	3	Digit 2	1
LASER Disk	6	Digit 3	2
Surround Sound	12	Digit 4	3
Cassette/Tuner	16	Digit 5	4
CD Player	17	Digit 6	5
Equalizer	18	Digit 7	6
		Digit 8	7
		Digit 9	8
		Channel +	16
		Channel –	17
		Volume +	18
		Volume –	19
		Mute	20
		Power	21
		Reset	22
		Audio Mode	23
		Contrast +	24
		Contrast –	25
		Color +	26
		Color –	27
		Brightness +	30
		Brightness –	31
		Balance Left	38
		Balance Right	39
		Standby	47

Note: Nowadays there are lots of smart TVs. Remotes of these smart TVs are multifunctional and commands are different. But the basic commands are the same.

Decoding:

The transmitted IR signal is received by a remote sensor. This sensor has a built-in IR detector and hysteresis comparator. As a result, the transmitted modulated signal is received as the SIRC pattern.

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Both the IR diode and IR receiver IC can sense the IR signal. But the difference is, the IR Diode can not decode the pattern from the received signal. And each IR receiver IC has a built-in IR diode inside along with a hysteresis comparator.

The TSOP4838 IR receiver IC is the active low type and we need to use a pull-up resistor with the output pin.

As the output is active low so the output is inverted. To decode the pattern, a start signal is sensed at first.

Then rest of the signals is decoded.

Flow chart

In the next article, we will make a circuit to decode the SONY SIRC Protocol and will make a device that can be operated remotely with a SONY remote. Today, this article ends here.

I hope this article will be informative to you and you can make your own decoder now. Thanks for reading.

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