Nanode - A Net Applications Node

Nanode - a £20 Network Applications Node for remote sensing projects.

Having worked with Arduinos for a couple of years, I was keen to extend the functionality and scope of the basic Arduino to include the ability to be networked with other Arduinos or devices via the internet or a local serial network - as the communication to the Arduino is fundamentally serial.
The opportunity came with the low cost NuElectronics Ethernet Shield, which provided an ENC28J60 ethernet controller and a Magjack for about £12, however by the time you had added an Arduino (and 20% VAT), the cost was approaching £40. The simplicity of the hardware was such that I reckonned that there must be a much cheaper way of getting internet connectivity - and thus the Nanode was conceived.

Combining an Arduino microcontroller and ethernet controller onto a single small board for developing networked sensor applications at minimal cost seemed an attractive proposition reducing the cost of net connectivity for microcontrollers by a factor of 2 - to an affordable £20!
The Nanode takes the standard ATmega328 microcontroller - as used in all the standard Arduinos, and combines it on a single board with an ENC28J60 ethernet controller and Magjack.

This was not the first time this had been done, Tuxgraphics produced the first one about 5 years ago as detailed in this article, and there was a very capable design on Instructables a couple of years ago. Indeed, almost all of the firmware for the ENC28J60/ATmega combination is derived from the original Tuxgraphics code.

So Nanode is not new, it owes its heritage to at least two previous designs, but it does introduce some new features which I hope will bring it more into the Arduino playground. Unlike previous designs it presents its I/O in a form which is compatible with Arduino shields, but also enhances the I/O capability with additional connectors - making the I/O more accessible when a shield is fitted and allows the device to be plugged directly into a breadboard and still access all of the power and I/O.

So after the initial idea was hatched, I had to make a prototype. I'd had a bit of prior experience breadboarding ethernet, so last August I combined the Microchip ENC28J60 ethernet controller and the ATmega328 and 74HC125 tristate buffer on a breadboard to prove the design. The combination of the 3 ICs and the Magjack on its breadboard friendly breakout board (from Cool Components) was a neat fit on the standard size breadboard. Cool Components source most of the key components, allowing the design to be built on a breadboard for about £12. A later post will describe the breadboard construction in detail - for those brave enough to follow this route.

So the Nanode, provides ethernet connectivity to what is essentially a standard Arduino and allows access to most of the original I/O lines for the control and sensor applications. To summarise you have 6 analogue inputs, 8 digital I/O lines and a serial port remaining after driving the ethernet controller. With this you can sense analogue variables such as temperature, pressure or energy consumption such as electricity or gas, and have the ability to control relays, displays or actuators using the digital I/O. The Nanode takes the serial interconnection one stage further and using some of the spare 74HC125 buffers implements a "multidrop" serial network - allowing Nanodes to be connected together on a local serial network, which provides communications and power.

Having built the first one up on breadboard, as a minimalist proof of concept, I got it working to the point where I could send messages or control packets to another network connected Arduino and NuElectronics Ethernet shield, using Pachube to transfer data between the nodes. Then I got distracted by other things and the "Etherduino" - the early construct name for the Nanode, got put to one side for 6 months.
It was on hearing that Pachube are hosting an Internet of Things Hackathon in London on April 8th/9th which encouraged me to revisit the design with the aim of having it ready for the Hackathon. The breadboard ethernet Arduino is now Nanode - a Network Applications Node. (Or Networked Arduino Node - for those in the Arduino camp).

Timing of the Hackathon was perfect, allowing me 2 weeks to finish my design and get some boards made. I also had wanted for some months, a general purpose DIY Arduino compatible board, which could be made more cheaply than commercial units. With the features of more friendlier I/O connections and had the means to be networked to other nodes on a serial bus, the Nanode seemed the ideal entry point into Net Connectivity for under £20.

Above: First Prototype Nanode Runs Pachube Client Code. Blue LED shows Ethernet data activty.

This new board was the opportunity to address some of the points on my wish list. There were several design points which I wanted to take into consideration and resolve:

1. Must be easy to build by anyone who can solder - so 2 layer PCB design (EagleCAD) using conventional and readily available through hole components. Board is 72.4mm 58.4mm (2.85" x 2.3") - marginally bigger than Arduino, to account for additional I/O connectors.

2. Low Cost - hence the use of the Microchip ENC28J60 ethernet controller.

3. Compatible with standard Arduino shields - matching connector pitch - warts and all!

4. More flexible I/O arrangement. I have fitted additional connectors on 0.1" pitch which allow compatibility with breadboards and stripboard. All of the standard I/O pins and power from the ATmega328 are available along one edge of the pcb, which simplifies plugging this board into breadboard or 0.1" stripboard. They also allow the I/O headers to be accessed even with a shield fitted. An extra connector in the top left corner brings up the analogue inputs and 5V power - so all of the ATmega I/O and power can be accessed from a single edge of the board with a SIL header pins - handy for one sided connection of everything to a breadboard.

5. Spare tristate buffers in the 74HCT125 allows several Nanodes to be interconnected on a serial bus, controlled by a master unit which is connected to the internet. This feature was developed last August and found that we could get 9600baud serial data down 300m of cable. Simple 4 way telephone cable can be used to string these nodes together.

6. With the ENC28J60 and Magjack omitted, the device becomes a simple serial node - at £5 lower cost.

7. Extra I/O connector allows direct plug-in of R/C servo or Moderndevices LCD display on 3 wire bus.

8. Serial accessed via FTDI cable or similar USB to Serial adaptor.

9. Tall headers will be used to increase the clearance between the shield and the Magjack connector - which is 3mm taller than the USB socket usually found on the Arduino.

10. Programmed through the Arduino IDE (or AVTdude) with access to the standard AVRISP 6 pin header.



BOM (Most specialist items from Cool Components in South London)

• ATMega328P-PU - DIP version Cool Components £2.81


• Microchip ENC28J60-I/SP - DIP version Cool Components £1.99


• 74AHC125D tristate quad buffer


• 3mm LED


• 1N4004 Diode


• 7805 Regulator


• 78L33 Regulator


• 16 MHz HC49-4H Crystal


• 25 MHz HC49-4H Crystal


• 51R 0.25W 1% resistor x 4


• 270R 0.25W 5% resistor x 5


• 2K 0.25W 1% resistor x 1


• 330R 0.25W 1% resistor x 1


• 10K 0.25W 5% resistor x 3


• Ferrite inductor


• 18pF ceramic cap x 4


• 100nF ceramic cap x 4


• 10uF 16V electrolytic cap x 3


• 28 pin 0.3" DIL socket x 2


• RJ45 MagJack £1.99 CoolComponents recommended


• 36 pin 0.1" SIL header x2


• Small Tact switch Cool Components £0.28


• ATmega Nanode PCB - that's me!
  

I have sent off to have batch of 10 boards made up in time for the Hackathon. If anyone would like the EagleCAD files, or purchase a pcb - please drop me a comment.