Building IoT incubator

Hello open-source and IoT community!

I paused development of mqopen for a while, due lack of spare time. But I got few ideas what to do and I'm in programming mood, so let's continue in development.

I'm experimenting with incubator project. I want to build very simple incubator for my sister. She is breeding cockroaches as feeder insect for her bearded dragon.

So, first some fact about cockroaches, particularly about Blaptica dubia species. They ideal temperature is about 28-30 °C. If temperature is higher than 30 °C, they lifetime is shorter. Also, the will not breed below 20 °C. They generally likes higher humidity. This species don't need that much high humidity, compared to other ones. But, high humidity leads to creating of mold. Recommended humidity slightly above 60 %.

Blaptica dubia are sexually adult after 8 - 12 months, so keeping them as feeder insect as quite long term run. If the colony dies, it takes long time to grow new one.

Incubator design

So, incubator should have following features:

• Sensor for measuring temperature and humidity in the colony.
• Relay for controlling the heater.
• 12 V power output for controlling computer fan.
• Alarm to notify user of something goes wrong.

Computer fan is experimental feature. It should ensure better air flow in the incubator box and potentially suck wet and warm air out. It is also supposed to be used in other applications, so 12 V power output can be useful.

Of course, incubator will be connected into network using MQTT protocol. It will report temperature, humidity or state of heaters, and potential alarms. It should be also configured over network connection.

Let me know if you like the project :)

MQTT node software

In last article I described a hardware aspects of my IoT endpoint device. Lets look at it software now.

Software must handle DHT22 sensor for measurements, implement enc28j60 chip driver, TCP/IP stack for it and MQTT client for sending data to network. My first requirement is to use plain C instead of using any Arduino software. Reason for this is it gives me lot more possibilities, smaller code footprint (I assume) and more convenient way to fixing a bugs. Also once a software is done, it can be very easily reused in another projects.

TCP/IP stack

Most challenging part of node software is TCP/IP stack. Fortunately, there is already quite good implementation called avr-uip, which is uIP project ported to AVR platform.

uIP is minimalistic TCP/IP stack written by Adam Dunkels designed for very small embedded systems. It is designed as event-based framework. It requires some learning, but it's not too hard.

My friend from our local hackerspace already made very similar project which uses this TCP/IP stack. So his work can be used as good reference point.

Only downside is that avr-uip is very outdated, so I had to make some changes to it and fix some bugs. But it works now.

Get it work

With working TCP/IP stack is very easy to get data from the AVR over the network. I found some another projects which implement enc28j60 driver, MQTT client and DHT22 driver, forked them and merged them into my software. I had to create man state machine and after some refactoring and bug fixes my node started to sending MQTT data.

You can find the code on the projects GitHub page. If you want to build your own MQTT node, please read attached readme file for configuration instructions.

Future features

I want to create more user-friendly device, which doesn't need to be manually configured for each build. Main features should be some DHCP client code to dynamically assign node IP address.

Another major feature should be DNS client to resolve local broker IP address from DNS server.

This could allow to develop very cheap plug and play device which doesn't require any configuration. One challenging aspect is very limited resources of used MCU, which has only 2kB of RAM.

Simple MQTT node

In the previous article I described a basic idea of building my network of interconnected devices. In next few articles I'll describe building of very simple sensor with network interface, which can send data using MQTT protocol.

Node requirements:

• Use well known Arduino hardware
• Software written in plain C
• Cheap components
• Scalable design
• Easy to use

MCU

Because I don't want to create my own board, I have to use some existing one. For that reason I decided to use well known Arduino Nano board with atmega328p MCU. I have lot of these in my shelf. This MCU has 32KBytes of flash storage for code, 1KByte of EEPROM as non-volatile storage and 2KBytes of RAM.

I have plan to use Arduino Pro Mini for final product. It costs about 2.50 USD on ebay.

Another advantage of using Arduino hardware is lot of existing code for it. I can easily connect some components, upload existing sketch and check, if my wiring is correct. After verifying that hardware is connected properly, I could start writing my own software. This safes me lot of work by finding bugs in both hardware and software.

Software

Although I'm using Arduino hardware, I'm not using any Arduino software. I decided to implement all software logic in plain C instead.

I thing that Arduino is really great for learning of programming microcomputers or to make quick proof of concept sketch. But its code is quite messy, not efficient and it limits many hardware possibilities. So for making some serious project it is insufficient.

Use of plain C has many advantages. You have complete control about memory usage and its optimization, interrupts, timers, power consumption and other things. You have to also create Makefile, which brings another control in code configuration, compilation and optimization.

Ethernet controller

There are two common Ethernet controller chips. WIZnet w5100 and Microchip enc28j60. W5100 is chip used in official Arduino Ethernet Shield. It has its own TCP/IP stack implemented in hardware and it is well supported by community. But it is twice as expensive as the enc28j60 chip. Because I want to make many of these devices, price is crucial. I had already some enc28j60 modules in my shelf.

Using enc28j60 chip requires more work in software. It requires to implement own TCP/IP stack in software layer. But it seems that this work is already done by someone else.

Sensors

For development purposes I decided to make a node only with DHT-22 (also known as AM2302) sensor. This sensor can measure relative humidity and temperature in 2s time period. DHT-22 is more expensive variant of DHT-11, which has very limited accuracy and measurement range.

I used this sensor mainly for development. Final software should be capable to use any other sensor or device.

Wiring

Finally, wiring of my prototype looks like this.

Next time I'll describe node software and building MQTT brokers.

New project – IoT mesh

Recently I started my new project with Internet of Things. My idea is to create mesh of sensors or some other devices connected to each other over the network. These devices should include some common sensors for monitoring temperature, humidity, barometric pressure, light and others. There also should be some logging devices for creating graphs from received data or monitoring network functionality. And finally I want to create some devices controlled over this network, like IoT enabled window blinds.

My basic design goals are:

• Reduce cost as possible
• World wide access
• Secure
• Reliable
• Easy to use
• Keep it simple
• 100% open source

MQTT

Basic building block for creating network of interconnected devices is communication protocol. There is already excellent protocol designed for IoT called MQTT, which meet all my requirements. It is designed to connect client devices over central server using publish/subscribe scheme. That means that every device send publish data into network tagged with topic. Other devices interested in some topic can subscribe to it and receive those data.

Central server is called broker. It is responsible for collecting messages from publishers and delivering them to subscribers. Broker can be also bridged to another broker. There is already open source implementation of MQTT broker mosquitto.

World wide access

Mosqiutto normally communicates in plaintext over TCP connection. It also can be configured to use SSL layer for encrypted data exchange. However, cheap sensors have not enough resources to use encrypted communication.

This problem seems to be solved by dedicating small MQTT broker in LAN secured by firewall and placed behind NAT. Clients in this LAN communicates with broker in plaintext. This broker then will be bridged to some central broker on the public Internet over SSL making secure connection. Whole network then should looks like this.

That's basic idea of my IoT network. Next time we will look at building simple MQTT device.