infraredmaterialsremote control
Some electronic devices' remote controls have their IR-diode covered with some glossy, dark acrlyic-glass like screen, others dont and you can directly see (and possibly touch) the IR-diode.
What is, however, the purpose of this cover?
And why do some remotes not require it?
What material is this cover made of?
Why is it dark (doesn't the dark toning diminish the amount of IR light being emitted)?
Infrared lasers do work as IR remotes in place of an IR LED. One must keep in mind that the laser needs to be modulated at the requisite carrier frequency (typically 36, 38, 40, 42, 48 or 56 KHz depending on the receiver). This precludes out of the box laser modules which have their on-board current regulation, and do not lend themselves well to modulation at high frequencies. Also, the cheaper TTL-modulated laser modules work up to perhaps 10 or 15 KHz, insufficient for the purpose.
A laser driver with TTL modulation input, that supports the desired modulation frequency and higher, will do the job. For example, this one works well as an ultra long-range TV remote for my Samsung TV:
(source: eBay)
However, here are the two issues with using a laser such as this one:
In order to aim at the IR sensor on an appliance, one would need to use an infrared visualizing ceramic strip stuck next to the sensor on the appliance, such as these ones:
(source: eBay)
(The keychain bit is just for convenience, since the imaging strips are rather thin and small, hence easy to damage or lose)
The ceramic material glows greenish when an infrared beam is incident upon it, providing a means for figuring out where the IR laser is aimed at.
Summary:
It can be done with a laser, but it is far too much trouble to be worthwhile.
No. Absolutely not. The "Last/Return/Previous Channel" button is a unique function code that the TV interprets!
For the most common IR control protocols, Philips' RC5, Sony's SIRC or NEC, the remote is normally an application-specific integrated circuit (ASIC) with hardcoded TV codes for fixed remotes or a microcontroller with a reprogrammable eeprom for learning remotes (programmed via special codes or through a programming interface like JP1 or even IR learning).
The remotes have a single code programmed into each button, and that does not change without intentional reprogramming. These codes are arbitrary for the remote and depend on the TV to interpret. You can see an example for Insignia TVs here: http://www.getzweb.net/jp1/data_returns/DeviceEFCs.php?type=TV&devid=1204&webpid=++396
Each of these codes are single function, unless you get into more advance macros which are a group of codes assigned to the same button that get sent in order.
Unlike some of the dubious test methods listed above, you can actually decode the actual code sent by your remote. All you need is a common IR receiver module and a microcontroller (MSP430, Arduino) or computer like the Raspberry PI.
A different way would be to use a IR Learning Remote like the Harmony remotes. If the previous button was an active copy of the last channels selected, then you could not clone the feature.
Further note, the On/Off button is typically a single code that the TV interprets as toggling the current state, but discrete On and discrete Off codes often exist for any given tv, as well as dedicated "Input Source X" button instead of "Next Input" type codes.
Best Answer
The cover is made of plastic that is opaque to visible light but transparent to infra-red. It probably attenuates the infra-red a small amount but not enough to affect operation.
The cover is basically for aesthetics - it will work fine without it.
Learning remote controls also have an IR photo-diode where there may be some advantage to filtering out visible light to avoid picking up other lights during the programming process.