Turning the iPhone into a universal learning infrared remote [ongoing]

Thanks to different applications in the AppStore, the iPhone can already be used to control a variety of devices that have some form of IP connectivity, like the Apple TV, the Tivo DVR or Linux-based DVR solutions.

Most consumer devices like TV sets, HiFi components or broadcast receivers only have an IR-sensor for remote control. The iPhone doesn’t have an IR-diode built in like other phones or PDAs which used the pre-Bluetooth IR method for data exchange, which was ironically introduced by Apple with their Newton MessagePads for use cases like “beaming” business cards.

So, to make the iPhone able to talk to those devices, additional hardware has to be connected to the Dock connector. I recently bought the SMD-variant of the Unzapper, which is an Atmel-based generic IR transceiver (meaning that it can send and receive IR codes). The Unzapper is a really nice device for testing, but it has certain disadvantages:

• The firmware currently doesn’t support sending custom code or learning. fd0, the developer, will add those features in the near future for the USB connection, then it will be quite easy to adopt that for serial connections.
• The 4 buttons, 2 LEDs, USB connector, ISP header & power connector eat up a lot of space. Perhaps this should be left out for a version that can only be controlled via other devices, but is a lot smaller.
• The whole circuit is designed to run on 6 – 12 V, which is stepped down to 5V for the mc. The iPhone can only supply 3.3V. Also, iPhone’s serial lines are described as accepting and dishing out 3.3V levels, making a level convertor or a lot of luck necessary. It might be nice to reconstruct the Unzapper to run on 3.3V only.

Here ist a comparison between the stock Unzapper and my slave unzapper. Note that the original crystal is still in place, it was sitting there to make USB connections possible. It might be removed, but that would break the compatibility with the stock firmware that is built to run on 16MHz. Also, the values of the caps, transistors, resistors and stuff has not been recalculated. Also, the net for supply voltage still says +5V. This is the voltage that is in that net when the device is connected to the ISP programmer, but when connected to the iPhone, the whole system runs on +3.3V. The ISP header is important for prototypes but can also be left out when the final system is optimized for size.

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Tags: control, infrared, iphone, ir, learning, remote, unzapper