Human Machine Interfaces (HMI) represent some of the most rapidly evolving technology existing beneath the IoT umbrella. Want a thermostat whose display brightens when it senses your approach? You’ll need a proximity sensor for that. A fitness band that monitors heart rate? That’s HMI, too. Devices that respond to your gestures? You guessed it.
Many (if not most) IoT applications require a variety of HMI capabilities since a large number of connected devices, such as security systems, smart thermostats and lighting control systems, may have a human interaction component. But how do 8-bit microcontrollers fit into this increasingly complex ecosystem?
Let’s look at three kinds of HMI and how they work within the IoT.
Capacitive touch interfaces can be used almost anywhere including under glass and plastic and are generally very robust and immune to noise. Silicon Labs’ capacitive touch MCUs offer a sub-microamp wake-on-touch average current and a 100-to-1 dynamic range. That means each pin conversion and detection happens in approximately 40 microseconds, the entire bank of 16 pins can be scanned in under 700 microseconds.
This exceptional capacitive sensing performance enables high-speed periodic scanning for activity as well as extended sleep intervals that reduce overall power consumption. Capacitive sensing technology is also perfect for buttons and sliders, such as those found on white goods, kitchen appliances and security touch panels. For example, the ultra-low-power consumption of a Silicon Labs capacitive sensing MCU can enable a remote controller using this technology to operate for 7 years on 2 AA batteries.
A segment LCD driver can be integrated into an 8-bit MCU or offered as a standalone, fixed-function device. As a standalone device, an LCD controller offers the best leakage and dynamic power characteristics of any LCD solution. This device interfaces to an adjacent MCU through SPI or I2C. It consumes so little current that it is possible to power the device from an input pin and completely forgo the VDD connection. Moreover, the die is exceedingly small and is best used as a bare die or chip-on-glass rather than as a packaged component. (See Figure 1.)
Figure 1. Example of Standalone LCD Controller
Gesture, Proximity and Ambient Lighting
Proximity sensing is highly desirable in many IoT end nodes as well as in portable medical and mobile computing products that require human gesture control and detection. Silicon Labs offers a family of 8-bit products supporting infrared (IR)-based proximity control as well as ambient and ultraviolet (UV) light sensing. For example, the Si114x MCU family implements proximity detection using one, two or three LEDs with a range of up to 50 cm, multi-dimensional motion sensing, heart rate/pulse oximetry and cheek detection capabilities.
This sensing architecture works in direct sunlight and includes a light sensor capable of sensing light levels up to 128 kLux. Light sensing technology often requires special packaging features, such as a transparent window around the light sensors. (See Figure 2 for an example of a proximity sensing MCU.)
Figure 2. Proximity Sensing MCUs Integrate Sophisticated Mixed-Signal Peripherals, Interfaces and Drivers
For sub-GHz star endpoints or flooding-capable RF stacks and space-constrained applications such as sensor nodes, a small footprint, ultra-low energy 8-bit MCU and RF transceiver, or SoC with integrated MCU and transceiver may offer the most cost-effective solution. For ZigBee mesh networking applications, a SoC with integrated MCU and RF subsystems might be the best option, particularly where PCB area is at a premium. Look for MCU and RF transceiver suppliers who offer low-energy 8-bit and 32-bit Cortex-M MCUs and wireless SoCs along with the development tools to simplify implementing the RF stack requirements.
Learn more about our 8-bit MCUs for the Internet of Things.