Successful Endeavours - Electronics Designs That Work!

IoT Impact

IoT Impact is the primary IoT (Internet of Things) event for 2018. It is supported by IoTAA (IoT Alliance Australia) and is being held in Sydney at UTS from 10 – 11 September. We will be exhibiting.

You can register with our discount code to get a discount on the conference part of the show. The exhibition is free but you need to register. You can register at IoT registration and use discount code IOTsuccessful-C1.

IoT Impact Awards

And some extra news, we are also finalists for the IoT Impact Awards in 2 categories: Enablement in IoT and Innovation in IoT.

IoT Impact Award Finalists

IoT Impact Award Finalists

The winners are announced at the IoT Impact cocktail reception which is held at the UTS Tech Lab which will also coincide with the opening.

For the exhibition we will be showing 2 custom IoT devices. The first is the arcHUB Smart Cities Sensor device and the second is a 15 year battery life NB-IoT water meter.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In AustraliaRay Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2018 Successful Endeavours Pty Ltd.

Smart 100

Each year Australian Anthill look select their Smart 100. This year the arcHUB Smart Cities Sensor Suite was selected as a Smart 100. This is an IoT (Internet of Things) device that is Designed in Australia, and Made in Australia.

Australian Anthill

Australian Anthill

You can read the full list of Smart 100 finalists 2018. Judging was done by the Smart 100 2018 Mavens and the winners are announced on 28th August 2018 at LaunchPad Evolve. You can get tickets at Smart 100 Awards 2018.

Anthill Smart 100

Anthill Smart 100

We will be there. We think the arcHUB is a revolutionary device and are pleased the judges selected it as one of the Smart 100 finalists 2018.

arcHUB trial at Fitzroy Gardens

arcHUB trial at Fitzroy Gardens

And an update. The Smart 100 2018 have been revealed in judges order with the arcHUB Smart Cities Sensor Suite developed for The Active Reactor Company coming in just outside the top 20.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In AustraliaRay Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2018 Successful Endeavours Pty Ltd.

Artificial Intelligence

There has been hype about Artificial Intelligence, or AI, ever since we starting thinking about creating it. Moves to create truly independently thinking systems are still struggling but expert and self-learning systems have made a lot of progress.

So I was interested to get an email from Karthik Reddy of 16best.net  with a new blog post from them about how brands are using AI to enhance their marketing.

Here is a snippet. Click on it for a more readable version.

Artificial Intelligence Use Now

Artificial Intelligence Use Now

The projection that really interested me is “100% of IoT initiatives will be supported by AI by 2019″. That is a pretty substantial claim. And of course not all the support will be in field as the processing power to make a difference is usually in the back end systems. Given we do a lot of projects for devices that fit the Internet of Things category I’m fairly confident that this is likely to be true. I’m not convinced it will be 100% but it will be high. And this is because once you have devices in the field gathering data, you start making connections between the data and outcomes, and then it becomes valuable.

A good example of this is the arcHUB Smart Cities Sensor devices. Once you have the data, you can learn a lot from it. And then you can start making better decisions. And then you can actually measure the improvements.

You can see all the details in How Brands Use AI including detailed statistics from many well known companies on how they are using AI.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In AustraliaRay Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2018 Successful Endeavours Pty Ltd.

IoT Change Catalyst

The Internet of Things, or IoT, continues to break new ground. Although there are still many things to be worked out, there is no doubt it will create new opportunities and enable value propositions previously unimaginable.

So I was please when Garrick Stanford from RS Components sent me an infographic looking at the way the Internet of Things will drive change. Here is his introduction.

‘Sometime ago we discussed exactly what the internet of things is. Well here we’re going to take a closer look at how it is going to change your life – and how that has started already. More and more technology and everyday devices and tools are now connected to the internet – think about your phone and TV, for instance. But here we’ll examine how the amount of connected devices that we use is going to hugely increase and how that will affect our lives.’
IoT Infographic on Change

IoT Infographic on Change

The one things we can be sure of is that this is but the start.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In AustraliaRay Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

Powering Telemetry

A big issue in the world of the Internet of Things, or IoT as it is abbreviated, is how to get power to remote devices. And this splits up into 2 separate but definitely related problems:

  • the power source
  • the power consumption

Obviously, if the power consumption is high, the power source has to be capable of providing a lot more power. We looked at this in our IoT – Remote Telemetry Case Study. So let’s tackle that one first.

And the focus for this article is remote devices using Solar Charging. Before we look at that specifically, let’s understand the problem.

Power Consumption

There are multiple ways to reduce power consumption. These were covered already in Reducing Power Consumption and Reduce Power While Awake with examples given in Sleep Saves Energy.

Low Power Sleep Mode

Low Power Sleep Mode

The short version of this is that you have to do 2 things at the same time:

  • reduce the average power that is consumed all the time
  • reduce the energy required to process an event

The first of these is also known as Quiescent Power Consumption. This is the power consumed just running the system when it is doing nothing, or close to it. At a minimum, the Power Supply has to deliver this amount of power just to make sure that we could react to an event, should it occur. And I can hear you thinking that it is hard to get this low enough and still have a responsive system.

Correct! But you have to have at least this amount of power or Game Over!

Which is where the second part comes in. You also need some power to respond to events. These can be something you need to log, or reports you need to post. If you are uploading to a web service using cellular communications, the peak power consumption can be very high. So you have to minimise this time.

We would normally model both of these and work out a power budget based on the worst case scenario model. Excel is a suitable tool for doing simple modelling of this as well as scenario modelling.

But I can hear you thinking “why worst case“? Answer: “Because you want it to always work, not just work on average“!

Telemetry

Telemetry means measurement at a distance or remote measurement. So you are measuring something at location A, and want to know the value of the measurement at location B. This implies the 2 locations are not close enough together that this is a trivial problem to solve.

In our world, Telemetry can mean anywhere on earth, though our customers are usually in Australia. In NASA’s world, (maybe world is the wrong term for them) it can be anywhere in the solar system. Voyager 1 is currently more than 18 billion Kilometres away and has been active for 40 years.

Artist's concept of Voyager in flight

Artist’s concept of Voyager in flight

The challenge for low power consumption, is how to get the measurement from location A back to location B?

Solar Charging

The NASA solution is simple. Near sun facilities are Solar Powered, and the rest use some form of nuclear power. Since no-one will ever let us nuclear power any Telemetry device, and I’m Okay with that, and we are near enough to see some sun, we will follow that option instead. And besides which, we can do it in our office and not a heavily shielded facility.

So lets recap on what we know about solar charging:

  • ignoring the energy cost of making a solar panel, the energy cost is free after that
  • there is a maintenance cost which includes cleaning panels
  • provided the construction is robust, they are a long life product
  • you have to do Maximum Power Point Tracking (MPPT) to harvest the most energy or minimise the panel size

And to get more power from a solar panel, you have to:

  • have more sun
  • have a better angle to the sun (cosine reduction)
  • have a better MPPT
  • handle lower voltages
  • use the right silicon

Not all Solar Panels are equal. If you want you panel to work in a mostly shady place then you might also want to use mono-crystalline Silicon solar cells because they are efficient and can continue to convert even low levels of light. In recent developments the efficiency of conversion had passed 25% as reported in Efficiency of Silicon Solar Cells Climbs and some of the stacked cell technologies are past 40% efficiency.

compact solar cell

compact solar cell

And then you have to harvest that energy. Which is where new devices like the SPV1050 come in. Experiments in our office showed that we can charge a Lithium Polymer battery from the internal lighting. And it is a buck boost converter meaning that it can charge the battery in full sunlight (reducing voltage) and also moonlight (increasing voltage) and the device costs less that $2 in 1K pieces.

I only have on criticism. The super low quiescent current LDOs would have been more useful if they were fully independent because this would have taken another item off the Bill of Materials.

Primary Cells

The other option for Telemetry is using Primary Cells. These are not rechargeable and so must last the life of the product. We currently deploy Cellular based Telemetry modules that can run for up to 10 years from a Lithium Primary Cell or 5 years from Alkaline Primary Cells. This is ideal for Smart City style projects where the devices might be moved as they fulfil their current purpose. A good example of this is people metering or pedestrian counting where a council may want to know how much use an area is getting. Once that is understood, the Telemetry module can be redeployed and since it isn’t connected to mains power you don’t need an electrician to do that. Or they could be used to understand the level of demand of public transport services in real time so you can adjust capacity on the fly.

So there are options and as technologies like NB-IoT and CAT-M1 come online the power budget for cellular communications continues to fall. We covered this in Cellular IoT Communications. And as of last month, Telstra turned on CAT-M1 across the 4GX network.

Quectel BG96 CAT-M1 Module

Quectel BG96 CAT-M1 Module

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In Australia. Ray Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

Smart Cities

Smart City is a blending of current and emerging technologies being employed to allow a city to better manage its assets and deliver value to its residents. It is an emerging concept and still very much in exploration. The 2 core technology areas being investigated as the primary value creators are ICT (Information and Communications Technology) and the IoT (Internet of Things).

Smart City

Smart City

What isn’t fully understood is the relationships between any or all of the list below:

  • what is worth measuring?
  • how to measure it (what sensor, what platform)?
  • how often?
  • in what detail?
  • to learn what from?
  • how quickly to transport the reading?
  • how much will it cost to transport the data?
  • via what technologies?
  • stored how?
  • accessed how?
  • analysed how?

Quite a big list.

Did you know there is a Smart Cities Plan for Australia? I only recently found out. And if you read through it there are more questions than answers. Which I think is the right balance given where we are positioned in trying to understand what is possible versus what is useful.

Smart Cities Plan

Smart Cities Plan

There are some obvious areas already being tackled by ICT systems. These include:

  • transport logistics (road, rail, freight, air, sea)
  • public transport
  • utility services (gas, water, electricity, waste)
  • weather prediction
  • environmental monitoring

And there are a range of trials underway to try and understand what using a broader sensor mix and more widely deployed sensors might do to improve amenity, even if they aren’t all very high quality sensors. Again the questions come back to:

  • what sensors?
  • how many and where?
  • how accurate?
  • how much do they and their platform cost?
  • measured how often?
  • at what latency?
  • what to do with the data?
Smart Cities Segments

Smart Cities Segments

IoT Challenges

Although the Internet of Things (IoT) has a huge promise to live up to, there is a still a lot of confusion over how to go about it. This breaks up into 3 distinct areas.

IoT Hardware

The first is the IoT Hardware device that is deployed to the field. These come in a wide range of shapes, sizes, power profiles and capabilities. So we are seeing everything from full computing platform devices (Windows, Linux, Other) deployed as well as tiny resource constrained platforms such as Sensor Node devices. Examples of the later are Wimoto Motes and our own FLEXIO Telemetry devices which are OS-less Sensor Nodes.

The trade offs are between:

  • power consumption
  • power supply
  • always online versus post on a schedule or by exception
  • cost (device, data, installation, maintenance)
  • size
  • open standard versus proprietary
  • upgrade capable (over the air OTA firmware or software capability)
  • security

As of a month ago, the KPMG IoT Innovation Network reported there are 450 different IoT platforms available. And most don’t talk to each other. Many lock you in. Many only work with their specific hardware. So picking a hardware platform is only part of the challenge. And new products appear every week.

IoT Innovation Network

IoT Innovation Network

IoT Communications

The second area of challenge is the communications. Everyone is trying to get away from Cellular IoT Communications because the Telecommunications Companies pricing model has traditionally been higher than they want to pay, and because the power required means you need a much higher power budget. So there has been a push to find other options which has opened the way for players like LoRa and sigfox.

However the CAT-M1 and NB-IoT Telecommunications Standards mean that the pendulum could easily go back the other way. CAT-M1 reduces the data rate (no streaming video needed for most IoT devices) and changes the modulation scheme so you get a better range at a much lower power consumption. And unlike sigfox, you aren’t severely constrained on how much data you can move or how often. CAT-M1 has just gone live in Australia on the Telstra network and we are about to do our first trials.

Quectel BG96 CAT-M1 Module

Quectel BG96 CAT-M1 Module

NB-IoT doesn’t yet have an official availability date but we aren’t too concerned about that. NB-IoT is really aimed at the smart meter market and similar devices which have low amounts of data and upload it infrequently. So a water meter running off battery for 10+ years is an example of what it is targeting. We will find CAT-M1 a lot more useful. And the modules that support CAT-M1 currently also support NB-IoT so we are designing now and can make the decision later.

IoT Back End

The third area of challenge is the back end. Pick the wrong data service and storage provider and you could find you don’t own your own data and you have to pay every time you want a report on it. And you can’t get at it to port it to another system. And if the volume of data grows the cost can grow even faster as many offer a low entry point but the pricing get expensive quickly once you exceed the first threshold.

Because of this there is an strongly emerging preference for open systems or for systems that do allow you to push and pull data as it suits you.

So our strategy to date has been to provide our own intermediate web service and then republish the data in the required format to suit the end user / client. The result is the best of both worlds. We can deploy resource constrained field devices which are low power and low cost, then communicate with high security and high cost platforms using the intermediate service to do the heavy lifting. And we don’t try and imprison the data and trap the client.

The service is called Telemetry Host and was a finalist for IT Application of the Year in Australia in 2015 at the Endeavour Awards. And again for the PACE Zenith Awards in both 2015 and 2016.

Telemetry Host

Telemetry Host

This isn’t the only approach and so we also create devices and incorporate protocols that allow them to directly connect to other systems. This includes porting our core IP to other URLs which are then owned by our clients. So far we haven’t found that one single approach suits every scenario.

Smart City

You can’t be smart if you don’t know anything. And this is certainly true for Smart Cities. To be a Smart City requires Sensors and Telemetry. But the jury is still out on how much and what kind.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In AustraliaRay Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

 

5G for IoT

Thanks to the team at VDC Research who compile some very useful information on Embedded and IoT (Internet of Things) trends. It is free to join and the deal is that you contribute to their surveys in order to get access to some reports for free. They also do detailed reports for business purposes which are available for purchase.

VDC Research

VDC Research

The following 5G IoT Infographic was put together by them to show the progression of 5G cellular or Mobile Communications in terms of its impact in the Embedded Systems and IoT space. If you click on it you will get a cleaner version to look at and you’ll probably want to zoom in a bit.

5G IoT Infographic

5G IoT Infographic

I was interested to see that there are still no fully confirmed standards for 5G. And my previous post on Cellular IoT Communications shows this to be a trend where NB-IoT is still being ratified even though there are chip sets on the market. It is also sobering to think about where all the data will get stored as devices running Gb/sec data streams will have to be sending it somewhere. Big Data keeps getting bigger.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In Australia. Ray Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

LPWAN = Low Power Wide Area Network

LPWAN is typically thought about as cellular data networks but that involves a contradiction since cellular and low power are inherently in conflict with each other. For instance, a standard 3G or 4G cellular modem will have a peak current draw of up to 2A during transmission and needs to be carefully power managed if running from batteries. This has meant that a 10 year operating life from a primary cell battery either needs a huge primary cell or very infrequent communications. So what are the alternatives?

In IoT Versus M2M we looked at how the real benefit of IoT (Internet of Things) is that rather than a single Machine to Machine link being established, there are now multiple devices connected via shared web services and their combined data is being used to create extra value, and particularly if Big Data analytics is added to the mix.

SigFox Logo

SigFox Logo

LoRa Alliance

LoRa Alliance

There is also a lot of potential disruption in this. LoRa and SigFox are both looking to provide lower cost networks to replace dependency on cellular network operators for coverage and also address the power consumption problem. There is an excellent comparison of these 2 systems in SigFox versus LoRa. And both are trying to disrupt existing cellular network providers. An overall view at available at NB-IoT versus LoRa versus SigFox.

NB-IoT

Which introduces Narrow Band IoT or NB-IoT as it is now commonly abbreviated to. Just to continue the confusion of acronyms, it is also called CAT-NB and CAT-NB1. There is a detailed view of this technology and its likely long term adoption at NB-Iot is dead – Long live NB-IoT.

The summary is that NB-IoT is too late to market and requires too much equipment changeover to win the early adopter market, especially in the USA, but will win in the long term. In the interim there is a host of other options also being developed. The cellular network operators have realised, at least 5 years too late, that their business and technology models were both under attack simultaneously. This is a particularly dangerous form of disruption.

Hardware is now becoming available and China adoption of NB-IoT makes them the  main early adopter market.

 

Quectel BC95 NB-IoT Module

Quectel BC95 NB-IoT Module

u-blox SARA-N2 NB-IoT Module

u-blox SARA-N2 NB-IoT Module

Low Power Cellular

So if up until now, low power and cellular were not usually compatible concepts, what is changing to address that?

To reduce power consumption, you have to have one or more of the following:

  • reduce transmit power
  • increase receiver sensitivity
  • reduce transmit duration
  • increase transmit interval
  • reduce network registration time
  • reduce data rate

Some of these can be mutually exclusive. However the key elements that are working together is to reduce the data rate and use a modulation scheme that means the transmitter power can be reduced. LoRa does this very well and NB-IoT is looking to achieve a similar thing. There are trade-offs and the lower data rate for NB-IoT means it is best suited to very small packets. CAT-M1 will require less power for larger packets because the faster data rate means the transmit time is a lot shorter.

Low Cost Cellular

So we have looked at the power consumption angle. How about cost and business model. And there are 2 aspects to cost. There is the hardware cost and there is a the network operations cost. To reduce cost you have to do one or more of the following:

  • reduce silicon and software protocol stack complexity
  • high volume production allows economies of scale for hardware
  • increase the number of channels available in the network
  • increase the number of simultaneous connections in the network
  • reduce margins

Both SigFox and NB-IoT aim to make the end device hardware cost as low as possible. In the case of NB-IoT and CAT-M1 the channel bandwidth can be reduced and so the same bandwidth can support multiple devices instead of just one. The power level in the device transmitter is reduced by reducing the bandwidth and data rate. As an example, a CAT-M1 module has a peak transmitter current draw of 500mA which is a factor of 4 lower than CAT-1. So low cost and low power can go together very well.

The graph below shows how the various cellular standards relate to each other.

Cellular IoT standards and how they relate

Cellular IoT standards and how they relate

IoT Deployment Options

We have been using standard 3G/4G Cellular modems for our broadly distributed IoT offerings. As of the end of this month, we ship our first CAT-1 based offerings. These have the advantage of supporting both 4G with fall back to 3G. Although NB-IoT hardware is available now from both Quectel and u-blox, the networks in Australia don’t yet support it. And while NB-IoT is ideal for fixed location assets, we also do mobile systems so these need to be CAT-M1 once it is available.

CAT-M1 is expected to be available in Australia on the Telstra network around September 2017. I am also taking this as meaning that NB-IoT is 2018 or possibly even longer. So we plan to move to CAT-M1 as soon as it is available. The modules are expected to be available about the same time as the network upgrades.

Here are some CAT-1 and CAT-M1 offerings from Quectel and u-blox.

Quectel BG96 CAT-M1 Module

Quectel BG96 CAT-M1 Module

Quectel EC21 CAT-1 Module

Quectel EC21 CAT-1 Module

The Quectel EC21 is what we are deploying in our units later this month.

u-blox LARA-R2 CAT-1 Module

u-blox LARA-R2 CAT-1 Module

 

u-blox SARA-R404M CAT-M1 Module

u-blox SARA-R404M CAT-M1 Module

IoT Network Upgrades

Ericsson have announced the roll out plans for the Telstra Network CAT-M1 capability.

And Telstra have announced their own Telstra IoT Network Plans.

This is the overall Telstra road map. Summary:
CAT-1 now
CAT-M1 by September
NB-IoT sometime after that but no dates yet

Other carriers will follow although Vodafone are well placed to introduce NB-IoT first as they have Software Defined Radio base stations from Huawei and so can roll it out as a software update.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In Australia. Ray Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

Connect Expo

The Connect Expo is on each year around late March in Melbourne at the Exhibition and Convention Centre. I had gone to previous events but this was our first time as an exhibitor.

Connect Expo - Successful Endeavours

Connect Expo – Successful Endeavours

This was by far the best Connect Expo I have been to. The mix of software vendors, web platform vendors, component suppliers and specialist IT vendors was excellent and there was also a specific section for eHealth. We set up our own IoT Platform demonstration with a QR code you could scan with a phone and take you to a webpage showing real time (less than 5 second delay) updates to the status of a device on the stand. A simple demo of the Internet of Things in action.

We will definitely be going again next year.

A really good trend I noticed was several Software Testing companies represented in the mix. Testing to confirm software is working correctly is a very important part of delivering a high quality product and it was good to see this coming through at the industry level.

We also shared the stand with Minnovation who do data science and analytics so it was also good to see how rapidly that area is expanding.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In Australia. Ray Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

Industry 4.0 and Bosch Australia

This is the first of a 2 part past covering the SEBN (South East Business Networks) business breakfast just before Christmas 2016. The first speaker was Gavin Smith of Bosch Australia. His talk was title “Life After Auto” and here is my summary.

Gavin Smith - Bosch Australia

Gavin Smith – Bosch Australia

In the 1960s you could make anything in Australia because the import tariffs were high and we were a long way away from the rest of the world. But by 2008 all that had changed. Although Robert Bosch is the largest tier 1 automotive supplier in the world, and the largest automotive company that doesn’t assemble vehicles, the original Bosch Australia factory is no longer there and a new one built and they are about to expand again.

So there is a lot of change. He also quoted Jack Welsh of GE fame: “If the rate of change on the outside exceeds the rate of change on the inside, the end is near”!

High volume no longer has to be a lot of the same thing. They are now doing high mix electronics manufacture and are about expand that as they have run out of capacity. This follows the Industry 4.0 model rather than traditional manufacturing.  The design team is also expanding s they are now do bespoke product design with the intention of making them locally.

Bosch are also keeping track of the following Megatrends:

  • Demography
  • Urbanisation
  • Energy and climate
  • Connectivity
Bosch - Megatrends

Bosch – Megatrends

And all of this relies heavily on IoT (Internet of Things) devices and Big Data. To be a global supply chain player or to have a modern product you will have to have connectivity and visibility of every part of your process and your supply chain as well. And for Industry 4.0 you will especially need it for inside the factory. This is already happening.

Robert Bosch are also looking at incubation for new ideas internally and also externally. This is a great idea and something we are also doing with both clients and prospects.

They are also looking to attract more women into STEM (Science, Technology, Engineering and Maths). Something I am also keen to see happen.

Industry 4.0 example

Gavin finished with a video that showed just how streamlined the Design to Manufacture path could become. Something essential to the realisation of a true Industry 4.0 mass customisation.

While it is worth remembering that some of the above is a view of how the Industry 4.0 future could be, rather than what today looks like, Europe have been pursuing this trend for 15 years. So we have quite a bit of conceptual catching up to do as well as implementation capability. And we need to start early which is why the Casey Tech School project and Schools of the Future are so important.

Successful Endeavours specialise in Electronics Design and Embedded Software Development, focusing on products that are intended to be Made In Australia. Ray Keefe has developed market leading electronics products in Australia for more than 30 years. This post is Copyright © 2017 Successful Endeavours Pty Ltd.

 

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