Electronics Design To Save Energy

We have looked at how Low Power Electronics is a green strategy because it reduces the amount of power that has to be generated.  And then we looked at a range of options for Reducing Electronics Power Consumption.

Now we are into specifics.  The last post looked at Sleep Modes For Microcontrollers and how extending the Sleep Period and reducing the Sleep Current could dramatically Reduce Electronics Power Consumption.

Saving Electronics Power When Awake

The next logical step is to ensure that Power Consumption when awake is also reduced as much as possible.  This can be a little tricky to get right as it can sometimes eliminate all the benefits you built up with you sleep strategy.  The reasons for this are:

• you can use Analogue Electronics to reduce software power requirements but it has to be turned off during Sleep Mode
• if you do turn the power off to Analogue Electronics then there is a Settling Time after it is powered up
• using Smart Electronics Chips can increase overall Quiescent Current
• unless the Startup Time and Shutdown Time are quick, these can dominate the Power Consumption

Now there are some Software Architecture issues that affect these, especially the last one, but we will look at that in another post.  For the last part of this post we will address the Electronics Design issues that have been raised here.

Electronics Design – To Save Power

Electronics Design can address these Power Consumption issues.  Here is an example of a Power Consumption curve where an RC Time Constant must be taken into account to minimise average Power Consumption.

RC Time Constant affect Power Consumption

Here is a list of general strategies to select from to reduce Power Consumption:

• using the lowest feasible Clock Rate so Clocked Devices use less power
• using shorter Settling Times particularly by controlling RC Time Constants
• select semiconductors for lowest overall Quiescent Current taking awake and sleep operation into account
• ensure streamlined Startup and Shutdown operation

The overall Quiescent Current issues often gives the most difficulty.  This can be addressed through Design Simulation either by SPICE, Software Modelling or a spreadsheet.  For simpler systems the spreadsheet is often the easiest solution to implement.  For very Software Intensive Systems the Software Modelling approach is the most reliable method.  This will allow you to construct scenarios and be able to predict the Power Consumption implications for each of them.

For our Electronics Design and System Test methodology we often create a full system Software Model and so it is easy to use this same Software Model to accumulate the power consumption as it runs.  This can also be automated and so simulate months of operation very quickly.

Next we will look at the role of Embedded Software in ensuring Power Consumption remains as low as possible.

Ray Keefe has been developing high quality and market leading electronics products in Australia for nearly 30 years.  For more information go to his LinkedIn profile. This post is Copyright © Successful Endeavours Pty Ltd.

How Does Sleep Save Energy?

For this post, we will look specifically at Embedded Software techniques to save power and energy.  This is a well known Power Saving Strategy which doesn’t always get the recognition it deserves.  It is also something you have to design into the Power Management Plan from the beggining.

For this example, we will use the MSP430 from TI which has some of the best Power Saving and Power Consumption figures in the industry.  We have used them to create devices that run from a pair of AAA batteries for 2 years and which have time based control algorithms so that they can’tbe used in a purely event driven mode.  Here is how it works:

Low Power Sleep Mode

This shows the power consumption versus time.  In Low Power Sleep Mode the consumption is close to zero.  Almost no power consumed.  Then depending on what is happening it wakes up to varying degrees.

Get the best Electronic Sleep

So this is how you take advantage of this:

• make the time between wake ups as long as possible
• make the time awake as short as possible
• only turn on the peripherals needs for a particular wake period

Now if you system only has to wake once every minute then you can get low power operation from a lot of different processors.  If it wakes many times a second then you need a processor that gives you lots of ways to reduce power during wake, reduce the time awake, and increase the interval between wakes.

MSP430 Sleep

So back to the MSP430. It has Power Conservation features that allow it to do all three better than most.  Here is the list:

• Digitally Controlled Oscillator DCO allows it to wake and run quickly
• Can run a Timer from a 32KHz crystal making interval timing very low power
• Can use the DCO to set the run speed and so shorten the wake time
• Lot’s of Power Down Modes so you can always find one that suits your application
• Peripherals can be Shut Down when not in use
• Can run down to 1.8V – more on that later but it can also help here

Low Power System Architecture

To take advantage of all this, you have to develop the System Architecture so that  takes advantage of this.  An example from a very long life application we did runs like this:

• 32Hz Oscillator runs a timer that generates a 1 second wake
• User input keys set up to wake on change of state from high to low
• Use DCO at 1MHz to quickly wake, execute & sleep again
• Use State Machines to allow modules to execute predictably with eratic timing
• Have early exit tests to prevent unnecessary Code Execution

The result is an application that runs a process with User Interaction, LED Indicators, and a 2 week cycle where the average Power Consumption is 20uA at 2.7V or 54uW.  Of this, less than half is the processor executing the software and the single biggest energy use is the intermittently flashed LED Indicators.

To learn more, check out this more comprehensive article on “Low power MCU selection criteria and sleep mode implementation” from embedded.com which provides more examples.

Ray Keefe has been developing high quality and market leading electronics products in Australia for nearly 30 years.  For more information go to his LinkedIn profile. This post is Copyright © Successful Endeavours Pty Ltd.

What is so good about Low Power Electronics?

If you read my last post, you would have noticed that this has the potential to reduce overall Power Requirements.  Up until now,  only Battery Operated Devices have really cared about Power Consumption.  If you could plug it into a wall outlet then all was OK unless you were consuming more power than a standard circuit allowed.

Today, things are different.  Climate Change is a global concern and reducing the Carbon Footprint for a product is important, regardless of what sort of power it consumes.

If we can reduce the Power Consumption of an appliance by 50%, then provided it’s Electronics Manufacture does not add that back again, we have a net Carbon Footprint gain.  In fact, if we can do this across all products then we will meet our Global Carbon Reduction target of 50% by 2050 with this strategy alone.

How to reduce Electronics Power Consumption

This is not a new topic, and much of what I present here represents the combined experience of the Electronics and Embedded Software industry.  Here is the short list:

• reduce the Supply Voltage for Microcontrollers, Microprocessors and CMOS Circuits in general
• use Sleep Modes and keep the Wake Periods as short as possible
• replace High Power Consumption Devices with Low Power Consumption Devices
• replace high utilisation Digital Filters with Analogue Electronics equivalents
• replace Polled Operating Modes with Event Driven Operating Modes
• use Low Power Smart Peripherals that Wake the rest of the System only when required
• reduce the Time To Wake and the Time To Sleep
• optimise the Software Execution Flow
• use Energy Harvesting
• Remove power from sections of Electronics Circuitry when not in use

There is overlap and interdependency between these but that is a good starting point.

Next I will start look at specific examples.

Ray Keefe has been developing high quality and market leading electronics products in Australia for nearly 30 years.  For more information go to his LinkedIn profile. This post is Copyright © Successful Endeavours Pty Ltd.

Low Power Electronics is a Green Strategy

There are 2 ways to reduce your Carbon Footprint.  The first is to get the same power from a Green Power Source that reduces the Carbon Footprint at the power generation phase.  This is where Wind Power, PV PhotoVoltaics, Wave Power, Geothermal Power and other such technologies come in.

Wind Power Generator

The second way is to use less power from the same source, which is a Power Reduction Strategy.  This is a bit different to the concept outlined in Unlimited Wealth by Paul Zane Pilzer where he shows that we keep finding ways to meet the expansion needs of the future. That is also happening.  The ‘use less power’ approach is about getting more from the existing. The great thing about this is that you can effect a reduction in you Carbon Footprint independent of the Power Generators and so this strategy can run ahead of large scale system changes.

First you have to have a baseline to measure from.  This will become critical for businesses that must show Carbon Footprint reductions once legislation in this area is brought in around the world.  The issue isn’t if, but when this happens, and what the specific details are.  Carbon Trading is an interim measure that allows money to be made off the problem while not actually ensuring there is real progress.  Eventually significant net reductions must happen.

Carbon Footprint Calculation

There is a Carbon Footprint Calculator available at IEEE.  You can see what your Carbon Footprint looks like by clicking on the IEEE picture below

IEEE Carbon Footprint Calculator

How did you go?  Some of the questions are not that easy are they?  We often don’t know the source of some of our power or the real Carbon Cost of our lifestyle.

Carbon Footprint Reduction

So reducing the Electronic Power Requirements for Electronic Devices is a primary Green Strategy for reducing your Carbon Footprint. For a complete system the calculation is of course much more complicated.  The survey above is aimed at households but the principle is the same.  A true Carbon Reduction Strategy requires you to consider not only your own operation but upstream and downstream operations as well.

This is of course only one strategy and we will look at others in the near future.  But for my next post I’ll concentrate on design techniques for Reducing Power Consumption in Electronic Appliances so that they become Low Power Electronics Appliances and help to reduce the overall Carbon Footprint.

Ray Keefe has been developing high quality and market leading electronics products in Australia for nearly 30 years.  For more information go to his LinkedIn profile. This post is Copyright © Successful Endeavours Pty Ltd.