Image source: Silicon Labs
It’s always great to have high-performance, low-power silicone for an IoT design, but the best choices can be undermined if there isn’t a good appreciation of RF range and power relationships to pick the right wireless interface. Fortunately, tools are available to make quick estimations and help pick from the many IoT wireless options for the optimum design.
Recently, Silicon Labs announced the EFM32GG11 Giant Gecko microcontrollers (MCU), the latest addition to its “energy-friendly” EFM Gecko lineup. Ironically, “Gecko” implies small, which was what the lineup is all about: high-performance processing and peripheral support, in a small, low-power package with lots of punch. Calling the new addition “Giant” seems contradictory, though it’s probably the best way to differentiate it. The Giant Gecko punches above its weight in capabilities, while lowering power consumption.
It has a 48-MHz, 32-bit processor, 1024 Kbytes of flash memory, 128 Kbytes of RAM, USB 2.0 for 12-Mbit/s communications, up to 93 general-purpose input/outputs (GPIOs), and high-end, 12-bit, analog-to-digital and digital-to-analog converters. It has a temperature range of -40˚ to 85˚C and comes in package sizes down to 7x7 mm and includes Advanced Encryption Standard (AES) encryption.
All these factors mean that it can quickly input, process and respond, in a secure fashion, to almost any range of sensor inputs a developer or user can throw at it, and do so in almost any environment. Typical applications range from industrial/building automation, to wearables and medical devices. That said, it may need protection from extreme heat and cold, or better still, find another option. For example, some MCUs are specially designed for operation in an engine compartment that can operate at higher temperatures, up to 125˚C and down to -40˚C.
As useful as the processing, memory and peripherals may be, the energy management and controls is the most interesting feature on the Giant Gecko. Along with its solid operating temperature range and small size, this is what makes it of particular interest in remote monitoring and other battery-operated applications.
The Giant Gecko has five different energy-management modes and operates off a 1.98- to 3.8-V power supply. The energy modes are:
- 20 nanoamps (nA) shutoff mode (0.4 microamps (µA) with real-time clock (RTC)
- 0.8 µA stop mode, including power-on-reset, brown-out detector, RAM and CPU retention
- 1.1 µA deep sleep mode, including RTC with 32.768 kHz oscillator, power-on-reset, brown-out detector, RAM and CPU retention
- 80 µA/MHz sleep mode
- 219 µA/MHz run mode with code executed from flash
The various modes help optimize for given applications. To experiment with the modes and features of the Giant Gecko, Silicon Labs also provides the EFM32GG-STK3700 starter kit, which includes all that’s needed to get a development project off the ground. It provides an LCD, ambient light sensor, inductive-capacitive metal sensor and support from Simplicity Studio.
More information can be found on the company’s website, and you’ll find that it’s a full chip-to-prototyping ecosystem for smart, highly capable, low-power IoT designs.
So what’s left for an IoT solution provider to do? That’s where it gets tricky.
Pick the Right Wireless Interface
Having all the right processing and energy management technology in the world can’t help if the wireless interface consumes more energy than is necessary to get the required data to the nearest gateway or other aggregation point. But which wireless interface is best? The options are many, and they vary in terms of required power at the transmitter and its antenna, the antenna gain, receiver sensitivity requirements, mesh capability and a host of other factors.
Recognizing that it’s difficult for non-RF experts to quickly figure out, back-of-napkin style, the range for a given application, it provides a downloadable tool that lets users input basic parameters and give a close approximation of what the design’s range will be.
For example, if a design is to operate in a particular frequency band, enter the output power from the system, the antenna gain, the receiver sensitivity and receiver antenna gain. Most of these parameters are available from the semiconductor manufacturer if they’ve developed a full development kit, or from a system provider.
After getting some basic system parameter information, the RF calculator tool can provide a good idea of the RF range for a given application. (Image source: Silicon Labs)
The tool, which is essentially an Excel spreadsheet calculator, will give an estimate of the range in open-field and office-like environments. The range varies widely across these two very different applications, as shown.
Use the right tools, either from Silicon Labs or other online resources, to get quick estimations of RF range and power performance requirements for an application before selecting an RF interface and band of operation. Then, combine that interface with the right hardware and software and optimize them both together to get as close as possible to the optimum IoT solution.