Decoding a digital signal

[simon72post]

Hello

I am wondering if someone could help.
A long time ago I had a device that plugged in to the serial port of my XP computer and was able to send IR signal to a minidisc machine.
I have lost the device but still have the software that worked with it.
So I have been looking at trying to make a new device to receive the signals from the computer and then send IR signals to control my minidisc.

The problem I am having is trying to decode the signal sent out from the computer. The signal comes out of the serial port on pins 2 and 3 its about a 6 volt signal. that stays high until its sending data.
I have already tried reading it as rs232 data in a terminal program using various baud rates and bit rates but just get rubbish out with the odd character but that is probably just random noise.
So what I did next was to use a IR led and IRscrutizer to read the signal and it looks like this (please see the attached screen shot).
Just to see if it was like the standard sony remote signal but its completely different.
So I still don't know what the signal is. I was wondering if anyone could recognize this type of signal and give me an idea what it could be.

 

[Tony Stewart]

There are standard modes of IR modulation for "0" and "1" using pulse width.

try decoding using common methods. and stds

 

[simon72post]

Hello Tony

Thank you for your response. But I dont think the signal is a Ir signal coming out of the serial port. The signal is completly different timing and pulse width. I think it is probably some serial signal. Like rs232 but so far have not been able to decode it. Could it be ttl.

 

[Nigel Goodwin]

Hello Tony

Thank you for your response. But I dont think the signal is a Ir signal coming out of the serial port. The signal is completly different timing and pulse width. I think it is probably some serial signal. Like rs232 but so far have not been able to decode it. Could it be ttl.

You're getting rather confused - and mixing apples and oranges. TTL is simply the voltage levels (0-5V), where RS232 more commonly refers to the actual signal itself, and 'most' RS232 is done at TTL levels these days anyway.

In your case, with an antique computer, the serial port should be a 'proper' one, with +/-12V RS232 levels - pretty poor from what you said, with only 6V levels?.

Is there anything on the other serial port pins?, when using ports in 'unusual' ways it's normal to use the handshake lines in strange ways, such as the way 'supposed' serial port PIC programmers work.

Sony SIRC's is pretty simple, and covered in my PIC tutorials, but I doubt you could actually generate the signal directly from a UART? - you could with the handshake lines though.

I would imagine the UART is sending data to a processor in the external module, which then does everything else - but I'd like to think it would just be sending standard RS232 data?.

Bear in mind pins 2 and 3 are input and output, so there should be no data on pin 2, only on pin 3.

Do you have a digital scope?, if so scope what's coming out of pin 3.

 

[simon72post]

Thank you for your response. What you are saying makes sense and is what I originally though. Its just I was unable to get any sensible data in a terminal. When I get a chance to connect it up and measure it with a scope I shall let you know what I find. Thanks.

 

[unclejed613]

Hello Tony

Thank you for your response. But I dont think the signal is a Ir signal coming out of the serial port. The signal is completly different timing and pulse width. I think it is probably some serial signal. Like rs232 but so far have not been able to decode it. Could it be ttl.

i've seen what IR remote signals look like, and what you have in the picture looks like noise, most likely from ambient light

 

[Nigel Goodwin]

Thank you for your response. What you are saying makes sense and is what I originally though. Its just I was unable to get any sensible data in a terminal. When I get a chance to connect it up and measure it with a scope I shall let you know what I find. Thanks.

With a scope you should be able to tell what baud rate it is, and number of start/stop/data bits - assuming it's RS232 - but coming out of the UART pin it can't really be anything else.