Serial IR receiver problem

The speed is normally set to 115200 in Winlirc, but I have tried different settings with no luck.

Amen to that!

I modified the circuit and run the zelscope. The results shows very little or no difference in the signal when the skype thing is attached and not. Screenshots here:

I guess that leaves me with trying another IR receiver or USB controler. I think I'll go with the USB UIRT.

That's the UART's data rate, but this interface isn't using the data part of the UART so that's irrelevant. I was wondering what the IR data rate is. If it's picking up the IR clock, which is commonly ~38kHz, it's going to need to sample at 76kHz, which is a sample every 13µs. If it's just being fed a presence or absence of IR clock (i.e. the IR data rate), then it's going to need to sample something like every 200µs. However, whichever one it uses, this just isn't going to work on a non-realtime system which is running other applications -- such use of a serial port just isn't what they are designed for and a more appropriate hardware interface would be required. Feeding it into a sound card might work better but would require significant changes to the associated software to retrieve the data pattern from the sound card.

Yep, seeing is believing. I think that rules out EMI leaving only things like the Skype software is monopolizing CPU time, disabling interrupts or interfering with WinLirc's use of the timer chip. I still suggest asking about Skype on the USB-UIRT forum before parting with the cash.

I wonder why "it has worked very well for many years now."

The TSOP1738 IR receiver module used in the WinLirc device demodulates the IR and outputs the baseband data. The PC merely needs to measure the durations of the pulses and spaces in the baseband data (by responding to interrupts when DCD changes). The data bits usually have periods on the order of 1-2mS.

I'm not sure I follow all that your saying, I'm not an expert on these things. I do however agree with the essense of your reasoning. The curcuit on the winlirc webpage is indeed simple (and cheap). I built it back in 2001 just for fun and to see if controling the PC with a remote was possible.

Will do. I will probably go with the USB-UIRT at sometime anyway and perhaps terminate the skype adapter if it turns out to cause more problems.

I'm sorry but I'm not sure I follow. Are you saying it shouldn't have worked well?

Sorry, I was responding to Mr. Gabriel who doesn't understand the WinLirc device, the TSOP1738 IR module, or how Windows handles comm ports but hasn't let that stop him from offering advice. WinLirc (and Lirc) have been around for several years and I don't recall seeing many complaints.

While the device you built is unconventional, it will work fine as long as nothing interferes with interrupt processing and/or access to the 8253/8254 timer chip. The Windows API has precision timer functions (which other apps might mess with) but it is also possible to access the timer chip directly using lower level routines and hardware registers. I haven't looked at any Lirc or WinLirc code to see how they time the pulses/spaces from the TSOP1738 but the hardware registers are independent of the OS.

You may even find that USB-UIRT uses the TSOP1738. There are almost identical IR receiver modules from numerous manufacturers (e.g. Sharp, Panasonic, Lite-On). I prefer the Vishay TSOP1100 since it handles nearly all Consumer IR carrier frequencies from 32-57kHz.

I would normally refer everyone to Ryle Design, who has an excellent tutorial on precision timing under Windows and who sells a DLL that provides low level access to the timer chip, but their web page has been down after they moved their operation from Michigan to Nevada.

For anyone interested, you can find a multitude of links dealing with the

8253/8254 timer chip. For example: