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View Full Version : What makes CIR, CIR?

07-27-2004, 04:47 PM
Is there a significant difference in the hardware with CIR and Fast IR? Can you make FIR, CIR by modifing the system internally?

I'm aware of the addon accessories but it would be cool to convert if you wanted to.

Jason Dunn
07-27-2004, 05:32 PM
The primary difference between FIR and CIR is the strength of the signal - CIR is meant to be used from across the room like a normal remote control, whereas FIR has a range of a few feet. I know of no way to convert FIR to CIR.

Robb Bates
07-27-2004, 06:17 PM
If the only difference between FIR and CIR is the output power of the IR LED, then you should be able to make an internal hardware modification. Most PDA with FIR implement it with an IrDA module which has some built-in timing circuitry. The output LED usually requires an external current limiting resistor. Now if you could use the signal coming off the resistor to drive a transistor which in turn drives a big IR LED, then that should work.

However, that's a bit of work. Plus, I'm guessing that it's one of those things where if you have to ask, then it's too complicated to do it yourself.


07-28-2004, 12:43 AM
CIR are made with more than one leds working parallel. this makes it impossible to modify non CIR devices to work as CIR

Robb Bates
07-28-2004, 04:18 PM
I disagree. If you're going to modify an FIR by adding a transistor and a more powerful LED, there's nothing to stop you from adding more LEDs, Parallel or Serial configuration.

And while some CIRs have parallel LEDs, many IR remotes I've seen only have one. All you need to do is increase the luminence of the output LED. But this whole discussion is probably moot since I don't know too many people that are willing to risk frying their PPC by adding bigger LEDs.

I also think the CIR in most iPaqs have some kind of extra timing circuitry. An IrDA module is designed for serial comms and does stuff like take a serial pulse train and chop the output LED signal into pulses 1/16th the period of the baud rate. Where as CIR modules are designed to store and reproduce the IR commands on top of a 38-40kHz carrier signal. It's only the fact that most IrDA modules can be overridden to send raw IR signals out and the PPC can modulate the 38-40kHz carrier signal using software. There are a few other issues to overcome when dealing with IrDA modules, like the automatic overcurrent cutoff when the output LED is turned on for too long. And other things...


Darius Wey
07-29-2004, 04:01 AM
It's definitely a hardware configuration. I remember back in the school days, they had to tune down the IR range (via a hardware modification) of HP graphic calculators because it was becoming too much of a problem during exams. So unless you're adventurous and want to get the screwdrivers out, I don't think you'd want to be experimenting on your device. :p

07-29-2004, 11:19 PM
Well, it looks like someone has already done a mod to increase their IR range with an older iPaq...pretty impressive.

Based on my little (pratically none) electronic engineering skills, it looks like he used a FET to amplify the IR signal. Shorted the gate and the source pins with a 100k surface mount resistor. He only had to figure out how to tap the IR signal look for power.

It seems all straight forward though finding the tap for the signal may be tricky. I'm willing to try, eventually, if someone can tell me what type of FET the guy was using and if it's available at a local Radio Shack. Any one?? :) :?: