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Proximity Sensor-Based RF Remote Control Forms Innovation Launch Pad

Nintendo changed everything when it introduced motion detection in its remote controls for the Wii. Along with altering the face of controllers, it also brought attention to potential applications for accelerometers, which have gone on change other industries. In the meantime, remote controls have continued to change, taking advantage of newer, more efficient wireless connectivity and human-machine interfaces (HMIs).

While infrared (IR) is still popular for remote controls, RF radios like zigbee have emerged as good alternatives due to their extremely low power, non-line-of–sight operation, and of course their mesh networking capability. This latter point allows them to be integrated into a home network and even become part of the Internet of Things (IoT), typically through a gateway.

Also, zigbee is well established and prolific, to the point that is has been integrated into MCUs such as the MC13213 from NXP, simplifying its use, lowering cost and power consumption, and decreasing footprint. These are all good things for remote controls and other wireless applications.

At the same time as accelerometers and zigbee, the HMI for electronic systems has also been evolving quickly. Touch control is now being applied everywhere, from laptops and home monitoring systems, to industrial control and automobiles.

There are many reasons for adopting touch control, including ease of use, cleaner surfaces and more aesthetic designs, as well as fewer moving parts, so products are theoretically more reliable. Also, with capacitive-type touch control, the proximity of the user’s finger is sufficient, so they don’t actually need to touch the sensor. All this is very much aligned with users that increasingly come at electronic systems from an intensely smartphone-oriented HMI experience.

So, maybe it’s a good idea to combine accelerometers, zigbee, and proximity-based touch control on a single device, with a smart MCU, or two, and see what happens?

Remote control gets wireless and sensing trifecta

That’s exactly what Freescale (now NXP) intended when it integrated zigbee wireless, an accelerometer, and proximity sensors into a proximity sensor-based remote control demonstrator board controlled by a low-power MCU (Figure 1).

Figure 1: The proximity-based remote control demonstrator board combines zigbee wireless and accelerometers, as well as capacitive touch sensing control. (Image source: NXP)

The design comprises a main control board, a small touch pad, and a loop antenna. The pad and the board are connected using a flat 5 double-wire cable (Figure 2).

Figure 2: The demonstrator board comprises the touch pad, main board, and loop antenna. (Image source: NXP)

The keypad is a contactless design that based on a 10-element electrode that is driven by Touch Sensing Software implemented on the main board on the MC9S08QG8, an 8-bit NXP MCU. The software has been specially designed adapted for the remote-control application, including accommodating plastic material. In this demonstrator board, the plastic enclosure comes from Ruwido’s Z-series.

The main board is where all the brains reside. Along with the MC9S08QG8 there is an accelerometer, the MMA7450L. The latest version of this is the MMA7341LCR1, a triple-axis device that has a sensitivity that is settable for ±3g/±9g, runs off a 3.3-V supply, and provides digital outputs to the main MCU, the MC13213.

The MC13213 is an 8-bit device with a HCS08 core that is integrated on the package with the zigbee RF 802.15.4 modem. The MCU takes the inputs from the touchpad controller (MC9S08QG8) and the accelerometer (MMA7450L/MMA7341LCR1) and performs the necessary processing to perform the requested function. Power comes via two AAA batteries.

Exploring possibilities for sensor and communication combo

While the initial application is a proximity-based remote control, that is only the beginning. It is, after all, a demonstrator board, and it’s demonstrating just one application and one set of user patterns and functions.

The board’s hardware and software comes with all the support of NXP behind it, so the controller can be used to explore many other applications and tricks to help differentiate a wireless proximity-based controller. A full schematic is also provided (Figure 3).

Figure 3: The full schematic for NXP’s implementation of a proximity sensor-based remote control is shown, but designers can play and experiment with an interactive version of the schematic here. (Image source: NXP)

It can detect motion and flash LEDs; the output of the MC13213 can be sent to another controller and merged with gyroscopes, magnetometers, and other sensors on a design that uses full sensor fusion and a better HMI and device control experience using the IoT.

The options are many, so take the baseline schematic and start noodling the interactive version here.