IoT Name Badge - Microcontroller

I recently introduced the hackable IoT Name Badge. With the selection of the microcontroller (MCU), software comes into the game of IoT applications!

Low-Power IoT Application

IoT is not only the microcontroller, furthermore the overall embedded application needs to be seen as one piece.

I had used many MCUs in the past which were mostly proprietary 8-bit, 16-bit and 32-bit architectures. In Europe MCUs of 意法半导体 are pretty common. Everybody knows Atmel Corporation AVR MCUs which is now Microchip . PIC is one famous MCU of Microchip . With Arm as game changer on the market, Arm Cortex M MCUs got very popular. Arm is licensing their core technology to silicon vendors, so they can produce their silicon with Arm Cortex core inside. Parallel there is also RISC-V coming, but so far I would highlight the Arm Cortex MCUs first, because there are existing some interesting players for low-power applications you never heard about.

Active vs. Sleep Mode

In general it must be differentiated between active mode and sleep modes. Active mode is the most attractive mode for running advanced software algorithms and #AI / machine learning. Deep sleep modes are interesting to save as much as possible energy while computing power is not required. Normally events/interrupts can be registered to get the MCU out of deep sleep mode into normal operation mode.

Deep sleep is normally dependent on the leakage current which mostly depends on the size of transistors on the chip. Bigger sized transistors having the lowest leakage. On the other side smaller sized transistors can drive higher frequencies with less power consumption. But also other technics can be used to save current, such as Subthreshold Power Optimized Technology (SPOT) from Ambiq

Think about a remote control for your TV: Most of the time the MCU will sleep and will wake-up on button press to send data to your TV. In this case it makes sense to choose an MCU with very low power consumption in deep sleep and more or less don't care about active current - but see the later on "Power Peaks of Death" chapter.

In the past IoT sensors were also often used in deep sleep and could wakeup by timer to acquire data periodically.

In modern applications IoT gets more and more active all the time, caused by very low power consumption also in active mode. By this fact, MCUs are getting interesting for sensor fusion or AI assisted event/pattern detection.

Power Peaks of Death

Another topic that needs to be taken in advance is power/current peaks in the IoT application. High-performance products with interfaces like WiFi can take up to 700mA current peaks. So in general having the application sleeping but waking up for active data-exchange helps to minimize the power consumption in average, but will cause energy storage elements to damage or to have a faster aging effect. So in general there is a strong need to minimize also the active mode power consumption for the future, also if a clever sleeping concept could help to minimize the average power over a long time period.

Transformation of the MCU market

In the past most semiconductor companies had series from low-power through general purpose up to high performance MCUs. Today Edge AI enabled MCUs are filling the gab by combining performance with low-power. Also Arm has launched some new Cortex M designs which have higher optimizations for neuronal networks eg. Arm Cortex M55.

e-peas EDMS105N MCU

A PMIC of e-Peas is already one part of the IoT Name Badge with their PMIC in the power supply. Beside energy harvesting PMICs, e-peas is also working on their first MCU. But what is special by this MCU? The MCU is an Extremely Low-Power Edge Devices Microcontroller for Sensing Applications (EDMS). "The EDMS105N general purposes microcontroller is based on the ARM Cortex-M0 32-bit architecture and presents an extremely low power consumption, both in active and standby mode."

The MCU is running at 24MHz with 18 μA/MHz, so 432μA in active mode and 340nA in deep sleep while RTC and 8kB of RAM are still active. So e-peas is offering an overall great MCU for active and deep sleep.

All together in a 6mm x 6mm QFN 48-pin package.

Ambiq Apollo Series MCU

Ambiq is also already part of the IoT Name Badge with their RTC for time-keeping and managing the way how to turn-off power and waking the whole system up by time events or external interrupts. But Ambiq has also Arm Cortex M MCUs in their portfolio. Apollo 1 - 4 are all Arm Cortex M4 MCUs which are running at around 500μA in active mode! Apollo 1 had started with just 24MHz while Apollo 2 has already 48MHz, Apollo 3 96MHz and Apollo 4 up to 196MHz! For sure beside the core, Ambiq had also added more and more peripherals and features in the past and in the meanwhile Apollo 510 adds Arm Cortex M55 with advanced #AI capabilities and a graphic sub system with again running in active mode with just some μW!

So Ambiq MCUs are great for always-on technologies where a lot of computing is done for most of the time. In addition Ambiq is a strong solution provider for powerful MCU driven #AI applications.

Infineon PSoC

英飞凌 had recently acquired Cypress Semiconductor Corporation . Cypress Semiconductor Corporation had a strong product PSoC which combines features of an FPGA and analog programmable part with a microcontroller. So besides running software in a MCU, it is also possible to design own programmable logic and programmable analog parts which can help to minimize power consumption.

英飞凌 offers a lot of different scalable components. In theory it is possible to design a whole IoT application with 英飞凌 components only.

MCU Selection

In general the MCU selection is not as easy as replacing parts one-by-one. There are some maker standards like Arduino which is making a replacement possible, but for sure is not the way the software is using the optimal way of implementation. Companies like the Raspberry Pi Foundation having beside the Raspberry Pi now also microcontroller available, but these are not low-power and the way Arm #CMSIS (Common Microcontroller Software Interface Standard) is implemented is also not the best at all.

But in general Arduino and Raspberry Pi Pico MCUs can be one solution to speed-up mockups and to challenge an idea with a hardware. Later on for the mass production, there is the need to do the selection again, but to be more application specific.

So what we had done for the hackable IoT name badge is a flexible implementation. On the one hand we had added the Raspberry Pi Pico footprint, so everybody with RP2040 know-how can easily start or at least has a lot of examples and forum discussions. On the other side we added the so called "future connector" which makes it possible to add MCU boards with minimal height and space using Molex莫仕企业布线网络部 502426-3230.

For the specific name badge IoT application we added UART, I2C, 2x SPI, 1x Camera, 3x PWM, 3x ADC, SWD (Debug), Reset and power pins.

The I2C bus is used with two QWIIC connectors and also some sensors for gesture detection, temperature, humidity, pressure, acceleration are already on board. A dual interface I2C memory with NFC interface makes data exchange possible with smart phones.

Wrap-up

In general it is not that easy to choose the fit for all MCU. Low-power is always dependent by:

• The whole IoT application
• Active power consumption
• Power consumption peaks
• Standby leakage current

In modern IoT applications, the active power consumption is dramatically reduced by different technologies. This helps to have higher computing frequencies available which results in shorter active periods.

There is a Raspberry Pi Pico footprint, so software engineering can be done easily for the first step. To be flexible for the future, the Accso IoT (hackable) name badge has also the future connector available, so also other alternatives from e-peas , Ambiq or 英飞凌 can be used!

See also:

IoT Idea: The hackable name badge

Hackable IoT Name-Badge - Power-Supply & -Management

CI/CD and DevOps for KiCad?