Steve Leibson

TI MSP430 Low-Power Microcontroller Demo Runs on Grapes

This TI video has been on YouTube for more than a year, but it’s new to me and pretty interesting. With all of the new low-power microcontroller announcements lately, this video is an excellent reminder that there are lots of good choices for low-power processors out there. If you don’t want to run your design on grapes, the video demonstrates that strawberries, kiwis, and other fruits are just as powerful.

Touchless Slider is One Cool User Interface, Driven by Low-Power Microcontroller

Silicon Labs has a diverse set of chips on offer and I’m really taken by the video demo of its new Si1120 Touchless Slider evaluation kit. The QuickSense Si1120 is an active infrared proximity sensor that you can use to build a variety of products with innovative, ultra-low power, touchless human interfaces. The chip itself incorporates an infrared LED driver, an infrared photodiode, an ambient light sensor, and control logic. The high-sensitivity infrared photodiode provides a single-pulse infrared proximity measurement allowing you to implement user interfaces using infrared light emitting diodes operating at unusually low power levels. The device is packaged in a tiny 3×3 mm clear surface-mount package and when it’s combined with a Silicon Labs low-power microcontroller, the Si1120 can be used for advanced motion and gesture recognition in products such as:

• Touch screens
• Instrumentation panels
• Kiosks
• Gaming systems
• Industrial interface
• Security
• Smoke detectors
• Residential HVAC
• Home appliances
• Toys
• Keyboards
• Fax/printer/scanner front panels

All this is just words. A video speaks volumes. So here’s the video:

The demonstration shows a user-interface slider board that incorporates an Si1120, two infrared LEDs, and eight visible LEDs. This board is controlled by Silicon Labs new ultra-low power C8051F900 microcontroller, which consumes as little as 160 μA/MHz in active mode and 10 nA in sleep mode with full memory retention. It will run on supply voltages as low as 0.9V. The microcontroller is based on an 8-bit, 25-MIPS 8051 controller core with a slew of peripheral devices including four timers, a UART, and a 12-bit A/D converter with a 15-channel analog multiplexer. The microcontroller is available with either 8 or 16 kbytes of on-chip flash and has 768 bytes of on-chip RAM.

Perhaps just as important, Silicon Labs supports this unique demonstration board with its QuickSense Studio development environment, a graphical environment wrapping multiple applications that guide user-interface developers through a development flow that includes graphical configuration wizards, firmware templates and performance monitoring tools. These programs interface with Silicon Labs’ QuickSense firmware API, which is a configurable firmware library that supports the development of many different interface types, from simple buttons to full gesture recognition. After configuring a project using the QuickSense Studio Configuration Wizard, the software simplifies the integration of human interface generates all the C code required for the selected functions.

I still find it hard to believe that a small 3×3 mm package can do all of this, but seeing is believing and the video makes a believer out of me. I’ve long been a user-interface enthusiast and the Silicon Labs Si1120 evaluation kit and demo board is simply one of the snazziest new user-interface components I’ve seen in quite a while. We’ve been watching lead characters use gestures to control sophisticated equipment for decades in science fiction movies and TV shows—most memorably perhaps in 2002’s Minority Report. Gesture interfaces, when combined with graphical displays are some of the most intuitive and most usable interfaces for all sorts of high-tech products and the Silicon Labs Si1120 looks to be one truly inexpensive way to implement a user interface that appears pretty darn sophisticated to an end user. Sophisticated user interfaces entice consumers to buy, so be sure to check out the new way to interact with your product. It’s clearly worth a few minutes of consideration.

7 Tricks from Microchip to Drop Power Consumption on any Microcontroller

Microchip is an incredibly successful microcontroller vendor with a massive array of chips to choose from. The company has a series of low-power microcontrollers and refers to them as NanoWatt XLP (extremely low power) devices. In support of those devices, Microchip published a chapter on “Tips ‘n Tricks” to wring every nanoWatt of waste out of a design using their brand of microcontroller, but the first seven tricks will work with any vendor’s microcontroller, so these seven are well worth reviewing.

1. Switch Off Unneeded External Circuits and Control Duty Cycle

Almost all microcontrollers from all vendors have multiple similar-sounding low-power modes (sleepy, snoozy, droopy, drowsy, etc.) Sounds like the silicon version of the Seven Dwarfs, right? Well, all the low power modes in the world won’t help application if your application code doesn’t manage the power consumed by circuits that are external to the microcontroller. Microchip’s document uses lighting an LED as an example. Just a single lit LED is equivalent to running most of Microchip’s PIC microcontrollers at 5V and 20 MHz. When you design your microcontroller-based embedded system, always decide what physical modes or states it requires and make sure the microcontroller can cut power to external circuits when their function isn’t required.

For example, cut power to that boot EPROM after your circuit boots if the first thing the microcontroller does is download code from the EPROM to the microcontroller’s internal RAM. Alternatively, if you’ve got a high-resolution A/D converter outside of the microcontroller—because perhaps you needed more than the 12-bit resolution provided by the on-chip converter—be sure to include a transistor in the external converter’s Vcc line so that you can cut its power when it’s not needed.

2. Budget Your Power

Calculate the amount of charge used by each system mode by multiplying the current in mA by the amount of time spent in that mode during one loop of the application. Then average the sum of all the results in mA*sec over the entire length of the application loop to get the average operating current for all modes during one iteration of the application. Divide that result by the length of the application loop to get average operating current. Use that figure to help you size the battery needed by using the battery’s mAh rating and the number of days, weeks, or years you want the battery to last.

3. Do Something Smart with Port Pins

All microcontrollers have configurable ports that may serve as input, output, input/output, or analog input pins. Make sure you always configure all of the microcontroller’s pins to use the minimum amount of power.

4. Use High-Value Pull-up Resistors

If you use a pull-up resistor to keep an input high, then make sure to use a big resistor to minimize current consumption. Don’t just use a 2.2K or 4.7K resistor from habit or rule of thumb. Maybe you can use a 10K resistor. Maybe 100K or 1M. The bigger the resistor, the smaller the drain on your battery.

5. Reduce the Clock Speed and Operating Voltage to Minimums

Don’t run the microcontroller any faster than needed for the system design. Then set the operating voltage accordingly. Each clock cycle drives charge through the microcontroller and that charge comes straight from the battery. Fewer clocks per second means fewer charge packets to suck from the battery and fewer clock cycles per second also mean the operating voltage can be lower.

6. Disable the Microcontroller’s Internal Voltage Regulator and Get the Core Voltage Elsewhere

If your selected microcontroller operates the processor core on a separate voltage from the peripheral circuitry, chances are you can disable the internal voltage regulator and supply that core voltage externally. The advantage here is that you can then set the core operating voltage exactly where you need it, not where the internal regulator wants it.

7. Use Schottky Diodes to Switch Between a Power Supply and Battery

If your system can be powered from either a mains-powered supply or a battery, you can put a diode in series with each supply and the diodes will automatically supply power from the source with the highest voltage. Use Schottky diodes to minimize power loss through the diode.

If you’d like to peruse the full text of the Microchip document, you’ll find it here.