[mythtv-users] Where to buy CommandIR ?

[Douglas Peale]

On 08/02/2010 02:01 PM, Brian Wood wrote:
> On Monday, August 02, 2010 02:55:41 pm Gert van der Knokke wrote:
>> Chris Hoff schreef:
>>>> Otherwise, you could try attenuating the signal reaching the STB's IR
>>>> receivers with something like multiple layers of white copy paper. If
>>>> you come up with something that works extremely well, do pass it on!
>>
>> If these emitters are simple IR LED's why not attenuate the current
>> through them by means of a simple resistor. Just keep increasing the
>> value up to the point the receiver stops responding then use a resistor
>> value slightly less than this. You could even use a adjustable resistor
>> in the range from 1 to 10 k or so.
>>
>> Good luck,
>> Gert
> 
> LEDs are not like incandescent lamps, you can only reduce the current so much before you get below the firing point of the 
> diode junction. You can't dim them the way you can a lamp, the usual way to dim LEDs is to vary the duty cycle, but that 
> won't work when pulsing the diode for IR transmission.
> 
> You might try a dab of not-quite-opaque nail polish at either end of the IR link, it might take some experimenting to find 
> a combination that works, transparency to visible light may differ from the transmission of IR energy.

You're thinking of neon bulbs.

You can dim LEDs by changing the resistance in series with them. LEDs operate at a fixed voltage, and the resistor is used to
adjust the current through them. The lower the resister value, the higher the current and the brighter they get (until you
exceed their current rating and they burn out). So yes you can adjust the brightness by changing the value of the series resister.