After running into the Pace Digital cable box IRDA code problem thread again, I decided to go ahead and see if it was possible to hand code an IR code for the Pronto which would allow simulation of carrier free transmissions.

My original premise was that if the Pronto carrier frequency could be set to the IRDA IR pulse rate and then modulated on/off very rapidly, one might be able to discretely control each pulse of the Pronto carrier. If once could do so, then it would be possible to hand code any IR pulse sequence by altering the number of on/off cycles of the carrier. To test this technique I used a solar cell and oscilloscope to visualize the IR pulse sequence transmitted by the Pronto. This allowed me to see the sequence of on/off IR emissions. The results were initially encouraging but I ran into some limitations.

0000 00ff 0005 0000 0001 0002 0002 0002 0003 0002 0004 0002 0005 0002

Successfully made the Pronto transmit a single pulse on of the carrier followed by two carrier times off, two pulses, two times off, three pulses, two off, four on, two off, five on. That was encouraging because that meant it was possible to get the Pronto to actually modulate the carrier wave down to single pulse resolution! Very encouraging, but then found some limitations.

1. If I tried a single carrier time off like

0000 00ff 0005 0000 0001 0001 0002 0002 0003 0002 0004 0002 0005 0002

the Pronto could not do it. There appears to be a fundamental limitation agains specifying only a single cycle of off time. Off time must be two cycles or longer. Well, that would be fine if we could set the Pronto carrier to twice the IRDA frequency so I tried increasing the carrier frequency like this....

0000 0030 0005 0000 0001 0002 0002 0002 0003 0002 0004 0002 0005 0002

This was identical to the first encouraging code but with a higher carrier frequency. This wasn't even as fast as IRDA pulse rate but already it was too fast for the Pronto to modulate on/off cleanly. Double the 115K IRDA rate wasn't going to even a possibility.

So it appears from my experiment that it isn't possible to modulate the Pronto IR carrier with sufficient precision to emulate high frequency carrier free IR transmissions like 115K IRDA. However, low speed 9600 IRDA might still be possible. Unfortunately, the Pace Digital box apparently uses 115K IRDA.

Guy Kuo
www.ovationsw.com -- Home of AVIA Guide to Home Theater

Hey Guy,
Do you have an upgradeable OFA or Radio Shack remote? Apparently, OFA has successfully developed a device code that can control the Pace cable box, using some kind of simulated IRDA signal. Maybe you could add the code to one of your remotes and shine it into your oscilloscope and see what it looks like. I seem to remember that people were not able to learn it into the Pronto, but you might be able to create the hex by hand to make it work if you knew what OFA had done to get it to work.

If you don't have an upgradeable remote, you might still be able to find a 15-1925 at some Radio Shack stores, it has an internal modem so you can add codes over the phone.

Rob.
http://www.hifi-remote.com/

I think there are two ways to do it, but I don't have a pronto, so I can't test.

1) IR sequences that start with 0100 instead of 0000 seem to be unmodulated. The number that normally determines the cycle time of the modulation, then determines just the units that the pulses and gaps occur in. Within each pulse, there are no cycles.

2) The first way is clearly better, but I think there is another way. Try to generate a very high frequency. One that exceeds the speed at which the Pronto can generate cycles and/or the pace can receive them. I think the cycles will then blur together into a half strength unmodulated pulse. (I have done this with other IR transmitting systems. I don't have a Pronto to test).

The hard part is not sending the right unmodulated signal. The hard part is knowing what unmodulated signal to send. You have some kind of IR detector. Do you have the Pace remote control? and is your IR detector good enough to tell you what bytes the Pace remote sends?

John, that is an interesting tidbit. I'll see what that looks like on the scope. If it gives direct on and off pulse controllability then it might do the trick. You're right, we don't know the Pace remote IR code sequences so actually getting things to work once past the low level encoding problem is yet another task. I undertook the experiment purely to see if the idea could work. However, I have neither a OFA or Pace remote and really don't have the time to decode the entire sequence. What I'm interested in is laying enough foundation at the low level protocol to know if it is even possible. Someone else will need to get the IRDA data sequences to finish the job.

John! That worked. Non-modulated pulses are generated with the 0100 lead in sequence. I've only tried a limited number of combinations but it looks like it IS possible to produce unmodulated pulses of arbitrary pattern. That means it is very likely that given the IRDA code sequences, the Pace remote codes can be hand coded!

Sounds like it might be possible to hand code the Pace Remote to the Pronto. Has anyone done that and if so, could we benefit from the results?
Thanks