Implementing a Smart Remote Control Using Bluetooth Low Energy and Embedded Processors

Virtual assistants will continue to be integrated into more devices in our homes. Amazon recently announced that it will be embedding Alexa into a variety of new devices, including earbuds, glasses, and even rings, giving consumers more ways to access more information. These new voice products are wireless and hands-free. The device effortlessly connects to your phone or other host and patiently listens for the commands to be issued. The wireless technology is through a Bluetooth RF chipset, and the processing is a dedicated embedded processor that needs to support wireless connectivity and run the wake-word engine (WWE) to recognize voice commands.

Another example of this trend is the candy-bar-shaped remote control that comes with every new flat-screen TV, set-top box, and media player. They will soon be completely wireless and hands-free, too. Of course, many tools will still support the old IR infrared when you want voice control, but these are quickly becoming obsolete. Users want a device that responds to their commands seamlessly, not like an intercom. Similar to recent Amazon products, the next generation of TV remotes will be wireless and hands-free.

However, remote control design presents some unique challenges. For example, remote controls are typically not rechargeable. They are usually powered by standard AA batteries. Not only do remote controls need to perform well in noisy environments, but they also need to be able to instantly transmit wireless information to a host device (such as a TV) from 3 to 9 feet away from your body.

Additionally, consumers prefer long-lasting batteries that don’t need to be replaced during the life of the device. Not surprisingly, most customer failures can be resolved with just a battery replacement. Consumer calls cost the company $30 to $50 per call, depending on the length of the call. Essentially, the remote had to perform like a wall-mounted Amazon Echo Dot while being more energy efficient than an in-ear headset.

The challenge of designing a powerful, energy-efficient remote control requires innovative Bluetooth solutions and audio processing solutions, as innovations in either or both can help battery life.

Using Bluetooth 5.0/LE solves two problems compared to traditional IR. First, Bluetooth is a standards-compliant solution, so it is easy for devices to communicate with the large infrastructure of existing Bluetooth devices. In addition, Bluetooth 5.0/LE provides a range comparable to WiFi devices, which is perfect for voice-enabled remote controls. Traditional Bluetooth solutions have been optimized for mobile phones and laptops, which tend to have larger batteries and where Bluetooth power consumption is not as important.

These two issues - larger batteries and power consumption - do not translate well to end devices such as remote controls. Companies such as Atmosic have revolutionized the design of total solutions by creating a foundational solution for consumer end devices such as remote controls. This design significantly reduces power (approximately 5x), and therefore can extend battery life 3x to 5x compared to competing solutions.  

In addition to the extremely low-power Bluetooth design, it is also possible to use an auxiliary wake-up receiver that consumes significantly less power (20 to 50 times less than a standard receiver), which puts the entire Bluetooth SoC into a deep sleep state. This part can be woken up by a special mode of another host. We will not go into detail about this technology here, as it is relevant to a small number of dedicated remote controls.

The third technique is to use energy harvesting (embedded in the Bluetooth SoC) to collect RF wireless energy to extend battery life. Many homes and buildings have a lot of RF energy (usually in the ISM band) that can be harvested while the remote is lying on a table. Depending on the energy level, the device can harvest tens of microwatts of energy to 1 mW. The goal is to replace battery power where possible and extend battery life to several years, compared to the current battery life of 6 to 9 months. For industrial and special purpose remote controls, other energy technologies such as light (solar), thermal, and motion can also be used.

As mentioned earlier, to achieve true hands-free operation, the remote must simultaneously function like a smart speaker, but be as power efficient as an in-ear headphone device. Companies like QuickLogic have created highly optimized ultra-low power companion devices that work with Bluetooth chipsets to meet this challenge.  

There are basically three modes for voice-enabled remote controls with Bluetooth connectivity: standby, wake-up word detection, and data transfer mode. The power consumption of the three applications gradually increases.

In standby mode, the Bluetooth and companion chip are asleep, waiting for some sound in the surrounding environment to wake them up. One of the most power-efficient ways to do this is with Vesper’s microphone’s “wake on sound” feature, which consumes only 10 µA to perform voice acquisition. In a typical living room use case, the system may be in this mode up to 80% of the time.

Once the threshold level is reached, an interrupt is triggered from the microphone and wakes up the companion chip into wake-word detection mode. The companion chip’s MCU can start and run WWE for a determined period of time to detect if the keyword has been uttered. Third-party solutions such as Retune DSP’s VoiceSpot WWE can run on the Cortex-M4 using only one microphone, eliminating the need for computationally intensive solutions with multi-microphone adaptive beamforming, which is typically required for mid-range (3 to 9 feet) voice recognition.

In addition to the obvious processing performance savings, removing a microphone from the system can save 400 to 650 µA (active power). If the wake-up word is detected, it will interrupt and wake up the Bluetooth chip to enter data transmission mode. This is necessary because the user word after the wake-up word needs to be transmitted to the host (TV) in the form of pulse code modulation (PCM) or compressed data.

If the wake word is not detected, the system reverts to the initial standby mode. Some companion chips, such as QuickLogic, have dedicated low-power sound detection (LPSD) hardware to reduce the average system power used in wake word detection mode. For example, some sounds, such as fans, have high dB SPL but are clearly not speech. The LPSD hardware is smart enough to sense and ignore the sound, avoiding the extra power consumption of running WWE unnecessarily.

Bluetooth 5.0/LE is well suited for data transmission mode as it can transmit data in low-power on-demand packets. The ideal partner should have enough storage and processing power to compress voice data before sending it to the Bluetooth device. A typical example is running the Opus encoder configured with four complexity settings.

Scott Haylock is the Director of Product Marketing at QuickLogic. He has over 20 years of experience in system-on-chips and holds a BSEE degree from Michigan State University. 

Srinivas Pattamatta is the Vice President of Business Development at Atmosic Technologies. He also has over 20 years of experience in wireless and other communications technologies. Srinivas holds a Masters of Science in Electrical Engineering from Oregon State University and an MBA from Santa Clara University.