Overview
By itself, your iPhone does not have the ability to send out the infrared signals used to control most home theater equipment. RedEye mini fills that gap. It runs off of the power your phone delivers through the headphone jack, so RedEye mini is completely portable, requires no batteries, and never needs recharging. Download the RedEye iPhone application, plug in your RedEye mini, and you are ready to go.
How Does It Work?
Please excuse us for a minute while we geek out a bit about RedEye mini.
More Than Just Audio Files and an LED
From the time that we announced the RedEye mini there has been a lot of speculation as to how it works, with the most popular assumption being that we stuck an infrared LED or two on the end of a headphone jack and play audio files to make the LED flash. While it is possible to fashion a remote control of sorts in this manner, there are some fundamental limits to this approach:
- Audio files can approximate infrared control signals well enough to control many but not all common home theater devices.
- Transmission range using only the power of the headphone jack in this manner is relatively short.
In other words, while it is possible to create a rudimentary infrared adapter using just a headphone jack, a couple of LEDs, and some software, the results are less than satisfying and far from “universal.” In order to make the RedEye mini a viable commercial product, we had to come up with an alternative approach to overcoming these issues.
A Tiny Modem
The first thing we tackled was the problem of faithfully reproducing infrared signals to control most any home theater device on the market. With very few exceptions, infrared remote controls use carrier frequencies between 20kHz and 60kHz, with the majority operating at around 38kHz. By contrast, audio playback through the headphone jack of a modern MP3 player tops out at around 20kHz. Although that may seem good enough, the Nyquist theorem states that in order to faithfully capture and reproduce a signal we need to operate at more than twice the frequency — or 40kHz to 120kHz. Since these frequencies are beyond the capability of the headphone jack, we needed to find another solution.
In order to reproduce these higher frequencies, we put a microprocessor into the RedEye mini. The mini’s microprocessor has no problems keeping up with normal infrared control frequencies, but the question was how to tell the microprocessor what signals to send. To accomplish this we turned the headphone jack into a small modem. We can send signals up to the mini’s processor through the left and right channels, and the processor can respond over the microphone line. Thankfully iOS gives us fine-grained control over audio playback and recording so we didn’t have to worry about keeping up on that side.
