Spinning up the SmarterBham project at Code for Birmingham


There are few things that get my inner geek as excited as the intersection of technology and the public sphere.  We have only begun to scratch the surface of the ways that technology can improve governance, and the ways we can put the power to transform the places people live in the hands of those people themselves.  This sort of civic hacking has been promoted by groups like Code for America for some time.  Code for America is loosely organized into “brigades” that service a particular city.  These independent units operate all over the US, and have gone worldwide.  Like any town worth its salt, Birmingham has its own brigade.  I first became aware of it back in 2015, attended a few meetings and then it fell of my radar.  The group produced a lot of valuable work, including an app for spotting and reporting potholes, contributions to open data policies, traffic accident analysis.

For about a year now I’ve grown increasingly interested in building IoT devices for monitoring various aspects of city life.  My first project was an air quality monitor (which is still up and running!).  At the same time I got interested in The Things Network and other ways citizens can participate and own the rollout of IoT projects at scale.  The price of technology has dropped so far and connectivity has become so ubiquitous that it is entirely feasible for a group of dedicated people to roll out their own IoT solutions with minimal monetary investment.

When these two things collided, something started happening.  Some of the folks at Code for Birmingham got excited.  I got excited.  Community partners got excited.  We made a plan.  We designed some things.  We ordered parts.  We started coding.  We made a pitch deck (because of course you need a pitch deck).  We applied for grants.  We built a team.  A couple months down the road we’re making serious progress.  One of our team members has made huge strides in building a prototype.  Another has started on our AWS templates.  We’re getting there.

Take a look at what we’re building and if you want to be a part of something awesome, get in touch.  We need designers, coders, CAD gurus, testers, writers, data wizards, and of course, some dreamers.  All are welcome.


Building an Open IoT Network in Birmingham. By the Users, for the Users

One of the big challenges in any IoT project is connectivity.  In a few proofs of concept and prototype projects I have worked on the choices have basically come down to either Wifi or 3G/4G connections.  Both are ubiquitous and have their place, but both also have significant drawbacks that hinder deployment.  Wifi usually requires access codes, has crap range, chews up battery and has FAR more bandwidth than most IoT projects really need.  3G/4G means a subscription or some kind of data plan and most carriers aren’t exactly easy to work with.  While platforms like Particle make this easier, it is still relatively expensive to send data and I’d like more choice in which embedded platform to use.  Are there any good alternatives?

Turns out there are, and one alternative in particular is appealing for the kind of open IoT projects that will drive us toward the future.  LoRaWAN is a Low Power Wide Area Network (LPWAN) specification governed by an open, non-profit organization that aims to drive adoption and guarantee interoperability.  With members such as Cisco, IBM and Semtech and an experienced board consisting of senior leaders from many of these same companies and others, the LoRa Alliance is well positioned to make this happen.  So that’s one possible standard but how does this enable an open IoT network?  How does it solve the problems laid out earlier and make some kinds of IoT projects easier (or possible at all)?

Enter The Things Network (TTN).  The mission of The Things Network is to create a crowdsourced global LoRaWAN network to foster innovation in much the same way as the early days of the Internet.  By deploying a free, open LPWAN, The Things Network hopes to enable innovators to build and deploy new IoT technologies that can change our communities.  That’s a mission I can get behind!  Check out their manifesto if you want to read about the full scope of their vision.

Our team seeks to built a Things Network community in the Birmingham, Alabama area.  We have already started reaching out to people across our metro in analytics, RF engineering, embedded systems, software development, entrepreneurship, community engagement / advocacy and government with the goal of building a consortium of local organizations to support a free and open IoT network.  Our vision is to build the open and transparent infrastructure required to support the future of smart cities.  Birmingham is a great place to do this.  The city center is relatively small so establishing full coverage should be achievable.  We have other smart cities initiatives in the works, including some things funded by an IBM Smarter Cities Challenge grant.  We have an active and growing technology community anchored by such institutions as the Innovation Depot, local groups like TechBirmingham and maker spaces like Red Mountain Makers.  We have active civic organizations with goals across the public sphere from economic development to air quality.  We have a can-do spirit and our eyes aimed firmly toward the future while being well aware of our past.

Assuming we can get a larger team assembled and this network launched, what do we plan to do with it?  A lot of that will come down to the people that join this effort and bring their own ideas to the table.  Initially the first few gateways will be launched in support of an air quality monitoring program using a series of low cost monitors deployed within the city.  Ideally this will expand quickly to other uses, even if those are just proofs of concept.  I, for one, plan to install a simple sensor system to tell me when the parking spaces in front of my condo building are available.  I hope others adopt this platform to explore their own awesome ideas and those ideas go on to inspire our city to become a leader in digital transformation.

I hope you will join us at the Birmingham Things Network Community and help us build the future one node at a time.

Building the DIY Air Quality Monitor – BOM and Pictures

A few days back I posted a bit about a DIY air quality monitoring project I’ve been working on.  That post just outlined why the project started, what we hoped to achieve, the high level design, component selection and software stack.  In the last few weeks the project has moved past the breadboard stage into a real physical prototype.  It’s a little ugly, built on generic perfboard and full of design compromises, but it works like a charm.  Now that it’s working, it’s time to share what went into the build, the bill of materials, and a few pics!

Top of board

On the top of the board I have mounted the Wifi module, the MQ series sensor array, a 6 circuit Molex connector for the particle sensor, a 5V regulator and the Arduino.  The Arduino mates to the perfboard using a bunch of 0.1″ male pin headers.  You can think of the perfboard as just a ridiculously, comically oversized Arduino shield.  The WINC1500 mounts the same way.  The MQ sensor breakouts use a right angle female pin connector.  Why so many connectors?  I like to reuse stuff.  With the way this is put together it is easy to pop modules on / off of the board to be reused in other projects or replaced if they stop working.  One thing to note here is that the Arduino uses wacky spacing for one of its sets of headers.  The spacing between pins 7 and 8 is not the standard 0.1″.  Why?  Who knows, seems silly to me.  I didn’t need one of those sets of headers, so I just left the problematic one with the weird spacing off of the board.

A word on power in this design.  The MQ series sensors all have internal heaters that are required to keep them at the right operating temperature.  These heaters need regulated 5V.  They consume more power than the Arduino has available from its 5V output.  So, 7.5V is fed into the regulator, which provides regulated 5V output for the MQ sensors and the DHT-22.  The same 7.5V is fed into the Arduino’s vin pin, which powers the Arduino itself.  The other low power items (WINC1500, Sharp particle sensor) are driven off of the Arduino’s regulated 5v output.  While it is possible to run the 7805 regulator without a heat sink for low current loads, my total load was high enough that it needed one.


Bottom of board

On the back of the board we find the Sharp GP2Y1010AU0F sensor, the DHT-22 temperature and humidity sensor, and a bunch of ugly globs of solder.  The one thing I don’t like about the Sharp sensor is the lack of real mounting holes.  It does have some little rails, so I used some short plastic standoffs and nuts to sandwich that rail and provide a secure mount.  The Sharp sensor’s data sheet prescribes a specific orientation for mounting.  Once this board is slid into its housing and the housing is stood up, the sensor will be oriented correctly.  The DHT-22 sensor is also mounted on this side of the board.  Why is that when it looks like there is plenty of room to mount it next to the MQ sensor array?  Recall that the MQ sensors have heaters in them.  The first iteration of this board had the DHT-22 right next to the MQ sensors on the other side.  When the MQ sensors came up to temp, the DHT-22 was consistently reading 10-15 degrees higher than it should have been.  Moving the sensor to the other side of the board seems to have corrected that.


Enclosure bottom

This type of enclosure is a pretty standard thing for sensors that live outside.  A louvered radiation shield keeps the rain and sun off of the bits and pieces.  Strong driving rain would probably still find its way in and I don’t want all these parts getting wet, so it will be mounted up under a covered area where it will stay nice and dry.  This particular shield enclosure was designed for an Ambient Weather temperature sensor but it works great for this project.  Luckily at its widest it was just a few mm narrower than the perfboard I used for the project.  Cutting a few little notches in the sides of the enclosure allows the board to easily slide in and out like it was designed to be there.  The oval shape of the enclosure cavity made part layout a little tricky.  The taller parts like the MQ sensors and dust sensor needed to be kept toward the middle so they would have enough clearance.


Bottom plate installed

The bottom plate has a standard power jack that is used to supply the system with power, and three status LEDs that show the state of the system.  Red means that there has been a fault detected and the system has halted.  When that occurs it will restart in 8 seconds or so when the watchdog timer kicks in.  The yellow light signals that the system is starting up, connecting to the network and taking test readings.  Green means that everything has started up and the monitor is successfully connected to the network.  It’s a bit crude, but does a good enough job to indicate the system status without having to hook up a USB cable and look at the serial monitor output.


All buttoned up!

The perfboard slides right in, and then the bottom two louvers are attached to the threaded posts with wing nuts.  Looks nice and clean once it’s all put together and you can’t even see that ugly board.


The posts on top of the enclosure are used to attach it to an L bracket included with the enclosure.  This bracket also comes with some U bolts that make it easy to mount the whole assembly to a pole.


Here’s what was used to build the monitor.  If you have been hacking around on electronics for a while you probably already have some of this stuff just laying around.  If you haven’t and you don’t have a good stock of bits and pieces, now’s a good time to order extras of stuff you know you’ll use a lot.  Passives, wire, that ubiquitous 0.1″ male pin header strip and of course you can never have too many LEDs!

I’ve put the wire in the BOM as well, even though it’s not strictly necessary.  I like the pretinned 24AWG stuff for laying out power and ground busses on one side of the board because it’s easy to solder it down to the pads on the board as you are routing it around. 22AWG stranded wire is good for connecting the board to stuff mounted on the enclosure (like the power jack) where some flexibility is needed.  The 30AWG insulated wire wrap wire is good for signal connections.  The 30AWG wire wrap wire is fragile though, so after I have it all working I like to tack it down with a dab of hot glue.  If you have to do some rework, the hot glue peels off easily enough.



  • 1x 10μF 25v electrolytic capacitor
  • 1x 1μF 25v electrolytic capacitor
  • 1x 220μF 25v electrolytic capacitor
  • 1x 150 Ω resistor
  • 1x 10k Ω resistor
  • 1x  each green, yellow and red LED




Moving from the breadboard to a real prototype was pretty straightforward.  With a good schematic and lots of pictures of the working breadboarded design translating it to the perfboard was mostly a matter of laying out the components in such a way that they fit neatly in the enclosure.  The schematic and Fritzing diagram will be added to the Github project shortly, they just need a little cleaning up.  If you are going to try a project like this, make sure you have your enclosure and bare board in hand at the same time or you may find that things don’t fit like you expected them to.  I was expecting the enclosure I ordered to have a larger cavity, for example.  Now that the monitor can be moved around without wires popping out everywhere we can move on to some real world testing, data collection and analysis.

Overview of Monitoring and Mapping Air Quality with Arduino, Node, Elasticsearch and Kibana

Almost anybody that lives in a decent sized metro area probably has air quality concerns.  My city has seen a lot of improvement in the past few years, but we still rank as one of the worst in the country for year round particle pollution, and we still have periodic ozone alerts throughout the summer.  The local wisdom says it is especially bad in the “bowl” of a valley in which the city sits. Shortly after Birmingham was founded, it grew rapidly as a steel town.  During this period of growth, the pollution in the Jones Valley was terrible.  According to many, this pollution led those with money and mobility to move up, and eventually over, Red Mountain.  In the 1970s the situation was so bad that a federal judge invoked the first ever use of the Clean Air Act’s emergency clause to have smokestack industry temporarily shut down.

Fast forward to 2017, and I’m looking for a new home.  While driving around house hunting with my incredibly patient spouse, we started talking about the advantages of moving from our loft downtown to the “Over the Mountain” neighborhoods and air quality came up as one potential benefit.  We’ve both heard how bad it used to be, and that better air may have been one of the reasons people moved where they did.  But, is it true?  Is the air quality in these neighborhoods any better?  Should we even factor that into buying a home in the same general metro area?  My wife is a scientist, and we share a desire to make good decisions with data.  Unfortunately, the data we have available on air quality in our metro area isn’t granular enough.  There are few sensors, and they are quite far apart.  This setup is good enough to get regional measurements, but not good enough to test some of our more localized assumptions.  To get what we want, we’re going to have to measure it ourselves.  Commercial measurement equipment is fairly expensive, and doesn’t easily lend itself to automated capture and logging.  Lucky for us, I’ve been having fun hacking on the Arduino platform lately, and there are a ton of great sensors for measuring different aspects of air quality out there for cheap!

Project goals

No project should start without an end in mind.  For this project, the goals are fairly simple:

  1. Measure the most common components of air pollution as accurately, precisely and discretely as possible
  2. Capture the time and location of the measurement
  3. Reliably record all of the measurements in a way that lends itself to easy analysis
  4. Be able to install as a fixed installation to measure trends over time in a single location
  5. Portable enough to take on the road to measure data in many locations in a short period of time
  6. Be able to take the data and use it to drive informed decisions
  7. Learn a few new things about air pollution, Arduino programming and electronics

The core platform

Logically, there are two separate parts to this project.  The first is a sensor platform that needs to be able to connect to the sensors, read data from them, and then send it somewhere.  The second part of the project is an aggregation and analysis platform that collects the measurements, stores the data and provides a way to use it to get useful insights.  This logical separation frees us to use tools that are well suited for each part of the job.  This simple little diagram shows all the pieces and how they fit together:


For the sensor platform I chose an Arduino Mega.  Why a Mega?  Well, there was one sitting in my parts bin, for one.  The Mega has plenty of IO to support a lot of sensors and other modules, and plenty of flash for a big program.  The Arduino Mega has more than enough processing capability to read from sensors and push data over a network, while still being low power enough to potentially run off of a solar panel or battery.  This is important to meet the project goals.  There are plenty of other devices in the Arduino family that could work just fine.

The aggregation and analysis platform was developed on my Macbook, but the final deployment target is a Raspberry Pi 3 rev B.  The Pi can easily run the software stack, is also low power so I don’t feel bad leaving it running for extended periods, and has enough GPIO pins to drive some other devices that will respond to changes in the air quality data.  One thing to keep in mind is that the Pi is an ARM7 based device, so anything that gets built on another platform needs to be portable to ARM7.  Another point in the Pi3’s favor is the built in Wifi.

Sensors and measurements

If you look at “real” air quality measurements from government agencies or other organizations, you’ll see a few things that most of them measure.  Particulate matter, ozone, carbon monoxide, VOCs and others are common to see in measurement suites, along with temperature and humidity which affect particle and compound formation.  I don’t expect to get absolute PPM / PPB measurements on par with professional gear, but for this use case that isn’t necessary.  A relative measurement that can be used to compare measurements taken in different areas is good enough.  A little digging on the internet led to a set of sensors that should get measurements that are good enough to compare different areas of town.  This list is by no means comprehensive, but these are the sensors chosen for this project.


The MQ-131 sensor measures ozone in the atmosphere.  Ground level ozone is known to cause a variety of health problems, and is a regular source of air quality alerts in urban areas.  Since my metro area sees multiple ozone alerts each summer, this is one that definitely should be measured.


The MQ-135 sensor is a general air quality sensor that is sensitive to smoke, NOx, CO2, benzene, alcohol and others.  It does not differentiate well, but for the purpose of this experiment a relative measurement of miscellaneous stuff you don’t want to breathe in is good enough.


MQ-7 sensors measure carbon monoxide.  CO is not something you want to breathe in, and is regulated by the EPA.  CO is most worrisome in enclosed indoor environments, but can also be a concern outdoors for sensitive populations.

Sharp GP2Y1010AU0F

Sharp’s GP2Y1010AUoF sensor measures particulate matter in the air using an LED to reflect light off of particles which is then measured by a photosensor.  Fine particles are a known source of health problems.  Typical air quality measurements look at two types of particles;  those that are < 2.5 microns in size, and those that are < 10 microns.  As far as I can tell the Sharp sensor isn’t sensitive enough to differentiate between the two classes, but for this experiment a total measurement of particulate matter is sufficient.


The DHT-22 is a simple temperature and humidity sensor.  Both temp and humidity can affect the formation of particles and compounds in the air, so it’s worth measuring for use in the air quality calculation.  Measuring temperature will also allow this experiment to map out the urban heat island effect.  This sensor can only be read every 2 seconds or so, but for this project that’s OK.

Connecting to the network

With the sensors selected, connected and happily spitting out data, it’s time to do something with it!  I’d like the sensor array to be located independent of the collection server, which means the sensor array should probably be able to send its data wirelessly.  The first iteration of this project used a CC3000 based Wifi shield.  If you are looking for a reliable wireless connection for your Arduino project, this is NOT it. Nothing against Sparkfun, it looks like a chip level issue and not anything in their design or library.  The CC3000 locked up so often that a watchdog timer became necessary to keep the system running for more than an hour at a time.  At its worst I measured over a hundred watchdog driven resets in a 24 hour period.  No bueno!  Switching to a WINC1500 breakout board from Adafruit helped immensely and now the monitor can run for days without a restart.

Inside the Arduino sketch’s loop() function each sensor is read in turn.  The data is then formatted as a JSON string, ready to be sent to the collection service.

Collecting and analyzing the data

Now that the sensor array is hooked up to the network and generating data, how can it be collected and analyzed?  This turned out to be the simplest part of the project thanks to node.js and Elasticsearch.  The sensor array formats the data as JSON and sends it along to a simple REST API built on node.js and Express.  This API in turn saves the data out to Elasticsearch for analysis.  The combo of node.js and Elasticsearch is lightweight and quite powerful.  Using Elasticsearch also gets Kibana as part of the deal, providing an easy way to search, slice and graph the results.  Simple and effective.  Kibana is great for displaying the graphs, but I also wanted to show running averages, minimums and maximums in an easy to digest way.  Another REST API provided by node.js accomplishes this using Elasticsearch aggregations.  That API is called by a simple web front end built in Angular.  Finally, I feel like this project is fully buzzword compliant!  Here’s what it looks like.  Not the prettiest thing around (yet), but it is effective!


The code

All of the code used for this project is available on my Github. Right now it is just a dump of the artifacts including the Arduino sketch and a simple node.js + Angular application to get aggregate statistics on the data. In the future this will include Fritzing diagrams and perhaps schematics and board layouts.  Oh, and some useful docs that actually explain everything!

Next steps

The next step for this project is to get a GPS hooked up so location stamps can be added to each reading.  As soon as the GPS is working, we’ll take the sensor array for a long drive around town capturing readings as we go.  Then it should be straightforward to take all of the captured data and map it out to see if our assumptions about air quality across Birmingham neighborhoods were correct or not.  Mappable data also opens the door to other interesting analysis, such as correlating readings with industry, income, etc.


Taken together the Arduino, node.js, Elasticsearch and Kibana provide all the tools an amateur citizen scientist needs to take some basic relative air quality measurements.  I hope others find this useful and share their improvements and/or data with others interested in what they are breathing.  In the near future I will publish my findings along with more detailed dives into sensor calibration and other related topics.  In the meantime, happy hacking!



Getting Started with an Activiti and IoT Example

In the second article in this series, we discussed several IoT protocols that might be a good choice to use with Activiti, and put down some questions that should be answered to guide the selection.  In this post, we’ll discuss the example use case, get answers to our questions, briefly introduce the hardware (covered in depth later), discuss the protocol stack, and the interaction with our BPM engine.

The Use Case

It’s hard to have a meaningful conversation about the interplay between IoT and Activiti without a concrete example.  For the purpose of this series, we’ll look at something basic:  A water sensor with an audible / visible alarm, and a remote shutoff valve.  The interaction between the components is fairly simple.  Water where it shouldn’t be causes an alarm to sound and a message to be sent.  This message triggers a remote shutoff valve to turn off, and notifies maintenance that there is a problem.  When maintenance accepts the task, the alarm is silenced.  Finally, when maintenance completes their task indicating that the leak is fixed, the remote shutoff valve turns the water back on.  The shutoff valve also needs to send an acknowledgement that the water is turned back on to complete the process.  The messages will originate from Arduino devices, automated and human tasks, and all of the activities will be coordinated by an Activiti process.

This simple example process encompasses both M2M (sensor -> shutoff valve) communication and M2P (sensor -> staff, staff -> shutoff valve) communications.  It also requires interaction between the process and IoT devices at multiple levels.  Our water sensor needs to be able to start a process instance.  Within that instance, we have tasks that need to send messages back to the sensor (to silence its alarm) and tasks that need to send messages to the shutoff valve (to turn the water on / off).  Looking back to the last post in this series, we had a few questions that can guide our early design decisions.  Now that we have a use case basically defined, we can get some answers:

  1. Do we just need to start a process, or do we need to be able to interact with tasks as well? – Both, for this case.
  2. Do we need Activiti to be able to push messages back to our device? – Yes, we do.
  3. Is there more than one type of device that may interact with a given workflow? – Yes, both water sensors and shutoff valves.
  4. Is there more than one type of workflow that may be started from a given class of device? – Not at this time.
  5. What triggers the interaction with the process?  Is it a single condition?  Is it a pattern? – A single condition will trigger the process start.
  6. How reliable does this need to be?  Is some loss or delay of messages tolerable? – We need a guaranteed message delivery.

Making Some Choices

Based on the answers to the questions above, it’s clear that we need a protocol that can guarantee message delivery and allows easy bidirectional communication between in-flight processes and devices.  The hardware in question is going to be a couple Arduinos; one for the sensor/alarm, and one for the valve.  The Arduino isn’t the most powerful device so something lightweight is in order.  MQTT fits the bill quite nicely.  It also helps that there are a few good MQTT client libraries available for the Arduino.  In addition to the client, MQTT also requires a broker to manage topics, clients and message delivery.  The Eclipse Mosquitto broker supports MQTT 3.1.1, is open source (keeping with the open theme of this project), and is under active development so it makes a good choice.  The final piece of the puzzle is missing and needs to be built:  We need a link between Activiti and MQTT.

Connecting Activiti and MQTT

Activiti is built on Java + Spring.  While it is possible to build some kind of a standalone gateway server to act as middleware between Activiti and Mosquitto in just about any language, the best impedance match here is to implement it in Java as an Activiti extension.  Like with the broker, it’s Eclipse to the rescue with the Paho project.  Paho offers MQTT client libraries for a number of languages including Java, Python, JavaScript, Go and C#.

There are two components missing from the picture so far.  Both depend on having an MQTT client running that is connected to our broker and subscribed to the necessary topics.  The first is a component that listens to MQTT for a new message that indicates a water leak.  This component also needs to know how to talk to Activiti so it can start a process instance. The second piece is a component that listens for Activiti events that need to be translated into MQTT messages and publishes them to the appropriate topic.  For the sake of simplicity, both of these components will be wired into Activiti as Spring beans, taking advantage of the hooks built into Activiti.  A bean that uses the process engine configuration hook point will start the connection to the MQTT broker to listen for messages that should start a process or affect tasks in an existing process, and a bean using the process engine event listener hook point will listen for the right Activiti events and pass those back through to the MQTT broker.

The extension described above can be generalized a bit.  XMPP and other IoT messaging protocols can be connected in much the same way.  It therefore makes sense to build a framework for connecting IoT pub/sub protocols to Activiti instead of just building a single integration for a single protocol.  This first example isn’t going that far, but the initial design should keep a framework in mind and once MQTT is working we’ll explore it further.

In the next article in this series we’ll (finally!) show the code, play around with a test MQTT client and see how we can actually start processes from MQTT messages.


Activiti and IoT, Choosing the Protocol Stack(s)

In part 1 of this series, we briefly discussed why it makes a ton of sense to use BPM to manage processes in an IoT world.  The pieces are all there, but how, exactly, can we make this work?  The answer to that question is, of course, “it depends”.  What kind of device are you connecting?  What sort of messages does it send or receive?  How much, if any, control do you have over these factors?  If you are building something from scratch with an Arduino or Raspberry Pi then it’s likely you’ll have a lot of control over what the device sends, how often, and what protocol it uses.  If you are deploying an off the shelf device your options will likely be much more limited or simply nonexistent.  A good place to start is to look at what kind of data you are working with and what protocol is used.  In my experimentation, I have been working with three protocols that are widely used in the IoT world: HTTP(S), XMPP and MQTT.


HTTP is a beautiful thing.  It’s easy to implement, easy to test, flexible, ubiquitous and mature.  You can use it to send any kind of data you want.  It has a nice set of verbs that map to the kinds of operations we might need.  HTTP is supported everywhere, with robust client and server implementations available in any language on any platform.  Done right, HTTP is extremely scalable.  Looking at the negatives, HTTP is pretty heavyweight when compared with some other IoT options and doesn’t offer multiple levels of quality of service.  This makes it reliable but that reliability is not always a requirement.  It’s also based on a request / response model which isn’t always a good fit for IoT applications.  If you want a long running Activiti process task to send messages back to your device it will need to be both a HTTP client and server, which is a lot to ask of a very low power device on an unreliable network.


XMPP was originally developed for instant messaging and presence applications as the protocol used by Jabber.  In subsequent releases it evolved into an IETF standard.  Today, XMPP is well defined but not stagnant thanks to an active community.  There are multiple client and server implementations across many platforms and languages.  The message format is flexible and extensible via XML.  XMPP supports a publish / subscribe model (via an extension), presence and a fairly rich set of features.  It is generally lighter than HTTP, but is still weighty on very low powered devices due mostly to the fact that it is a text based protocol.  XMPP, like HTTP does not support multiple QoS levels.  This makes it suitable for IoT devices that have a fair amount of power and need reliable message delivery.


MQTT is the lightest of the protocols that I have been researching.  It is an OASIS standard supporting a publish / subscribe model, and has a number of client and broker implementations available.  MQTT isn’t quite as widely used or supported as either HTTP or XMPP, but it is mature and stable.  MQTT is a binary protocol designed for constrained devices operating on unreliable networks, which means it is very well suited for IoT applications like remote sensor networks.  Support is included for multiple levels of QoS ranging from “fire and forget” to guaranteed delivery.  It isn’t great for large amounts of data, and is not as flexible or extensible as either HTTP or XMPP.


There are a huge number of protocols for IoT devices both open (to varying degrees) and proprietary.  For my purposes I’m not even going to look at the proprietary protocols because proprietary protocols are dumb.  The real value of IoT can only be realized through openness and integration, not through secrecy and walled gardens.  Some other open protocols that may be worth a look depending on your needs include AMQP and STOMP.  These may get their own articles in the future, but for now I’m going to focus on the three described above.

Connecting to Activiti

Assuming we now have a device and a use case in mind, we know what its data and delivery reliability requirements look like and we know what protocol we are going to use, how can we get this thing talking to Activiti to either start a new process or interact with one that is already in-flight?  Again, that depends.

At its simplest, your IoT device could simply call one of several REST APIs in Activiti to start a workflow.  You could call one of the workflow initialization APIs directly to start a workflow using a message or a process definition.  This sort of simple point to point integration works, but it is hard to scale without excess complexity, hard to maintain and brittle. A better option, if you are going the HTTP route in your IoT project, might be to push the message onto some kind of bus.  Either way, if your device speaks HTTP, getting a basic connection to Activiti that you can use to start a workflow or interact with tasks is straightforward.  What about other options?

Using another protocol with Activiti will require some sort of bridge or gateway since Activiti doesn’t speak MQTT or XMPP natively.  Each of these protocols uses a different architecture and will require a different approach.  Even so, we can map out some high level requirements by asking a few questions about what we are trying to do with our IoT project:

  1. Do we just need to start a process, or do we need to be able to interact with tasks as well?
  2. Do we need Activiti to be able to push messages back to our device?
  3. Is there more than one type of device that may interact with a given workflow?
  4. Is there more than one type of workflow that may be started from a given class of device?
  5. What triggers the interaction with the process?  Is it a single condition?  Is it a pattern?
  6. How reliable does this need to be?  Is some loss or delay of messages tolerable?

In part 3 of this series, we’ll outline a simple use case, introduce our example IoT device and code, answer the questions above for our application and get a basic gateway working.

IoT, Activiti and the Workflow of Things

I’m not going to waste much space here writing about the broad, general impact of the Internet of Things.  Countless column inches have already been spent detailing the number of devices, the amount of data and the potential size of the market.  We get it, it’s huge, still growing and transformative.

One of the most interesting facets of the Internet of Things is the complex flows that result from simple events.  A single out of spec sensor reading can trigger a cascade of machine and human actions.  Deviations from known patterns of data might mean nothing, or may signal some kind of catastrophic event.  How can we tell the difference?  How can we orchestrate a response to conditions that are signaled by our IoT data streams in a consistent way whether or not human intervention is required?  How can we look at these responses in aggregate and find ways to handle them more efficiently, find opportunities for further automation or discover exceptions that our current process does not cover?

This is not a new problem.  We have been dealing with the challenge of coordinating activities triggered by signals or messages at scale for years.  While the source of the messages (high volume IoT event streams) may be new, the techniques for responding to them are not.  We can leverage many of the same tools and patterns that have been used successfully in other spheres to coordinate actions that arise from IoT events.  Specifically, we can take advantage of a scalable, high performance workflow engine to consume the output from IoT devices, decide what messages or message patterns indicate an action is required and then execute a process in response.  The beauty of this approach is that it gives us a clean separation between the underlying data and the process design, using tools and concepts that are already well understood by business and technical users alike.  Our process engine can intelligently interact with other IoT devices using automated workflow tasks (covering many M2M use cases) as well as tasks that require human intervention (solving for many M2P use cases) or both in the same process.  Finally, this approach gives us access to detailed analysis of both in-flight and completed processes without having to reinvent anything.  In short, IoT and BPM seem destined to connect and in some ways, converge.

This is just the first in a series of articles.  Over the course of the series we’ll explore this idea in more depth, discussing how a number of IoT protocols can play in the BPM world, how we can structure bidirectional communication between our process engine and IoT devices, where we may need new components, and how to use the insights BPM analytics gives us to make sense of trends in our IoT data.  When we need to build specific examples, we’ll make use of Alfresco Activiti. Activiti is well suited for this kind of thing.  It is lightweight, super fast and scalable, and comes with analytics baked in.  Most importantly, it is open source and easily extensible which we’ll need to build some of our examples.  It’s a perfect fit.

Stay tuned for the next article in this series, “Activiti and IoT, Choosing the Protocol Stack(s)“.