Sunday, May 08, 2011

Nanode 5 - Progress Update

A bit of an early start this morning as my cat woke me at about 4:30am. By 4:50 I was up and starting to finalise the Nanode 5 pcb layout.

Nanode 5 will be the first commercially released version and it has undegone significant improvements since Nanode 2 - the first prototype board.

The Nanode development team has gained a lot of experience in the last month since the prototype was first shown at the Pachube Hackathon. We have taken the opportunity of these last 4 weeks to update the design and make sure that it meets all the expectations, and we have crammed in some new features.

Following our recent build session in Snowdonia it was decided that from the outset, Nanode 5 should make more use of wireless and be easily configured as an ethernet to wireless bridge. We have decided to take full advantage of a low cost wireless transceiver module by Jee Labs.

So I have updated the circuit and connectors slightly so that the Jee Labs RFM12B transceiver breakout board will plug directly into one of the Nanode expansion connectors. This board is available for about £11 as a full kit or £4 for a bare pcb from Jee Labs shop. With this board, the Nanode 5 functions just like the JeeNode with ethernet, so we can make use of all of the applications firmware already developed by Jean-Claude Wippler at Jee Labs.

One of the limitations of the ATmega328 processor is the 2k of RAM. This can be partially overcome by fitting an external memory device. The SPI bus lends itself to communicating with such devices with a low pin-count interface. On the bottom of the Version 5 Nanode board we have included a footprint which will accept an 8 pin SPI memory device. This can be SRAM, FRAM or EEPROM/Flash and accept devices up to 256Kx8. Extending the memory of the Nanode will be useful for many applications. The device can be purchased for about £2.

Nanode also has a footprint to accept a unique ID MAC chip produced by Microchip. This contains a 48bit unique identity plus 2k bits of EEPROM memory which can be used for storing the Nanode configuration etc. This device is 38p from Farnell.

As a result of the aim to have full compatibility between JeeNode and Nanode, we have had to move some of the SPI chip select lines around. Here is a quick list of the main I/O pin functions:

Digital 0 Serial Receive
Digital 1 Serial Transmit
Digital 2 Interrupt for RFM12 wireless and ENC28J60 ethernet controller
Digital 3 Interupt for Vusb - virtual USB
Digital 4 Virtual USB data pin. Servo control output, Display output with software serial
Digital 5 Used by Nokia 3310 LCD shield
Digital 6 /TXEN - enables the transmit line to local serial bus. LED indicator
Digital 7 Data input/output for MAC chip

Digital 8 Chip Select output for ENC28J60 ethernet controller chip
Digital 9 Chip Select output for SPI memory chip
Digital 10 Chip Select output for RFM12B wireless tranceiver module
Digital 11 SPI MOSI
Digital 12 SPI MISO
Digital 13 SPI SCLK

In addition to the above signals, the expansion connector also has +5V, 0V and +3V3 to allow the RFM12 module to plug straight in. Digital 8 and digital 9 have been removed from this connector as they are used internally by the ENC28J60 and the SPI SRAM as chip selects. They do however still appear on the Arduino shield connectors as standard.

As you can see a fully populated Nanode with ethernet, wireless, SPI memory and a MAC chip is going to be pretty much maxxed out in terms of available I/O. However a wireless only node, or serial node will have a lot more I/O available for the users sensor application - essentially 6 or 7 digital lines and 6 analogue inputs.

Of course a Nanode pcb can be partly populated with just the ATmega328, crystal and reset circuit and used as a very low cost Arduino clone. This could be a very cost effective way to get a load of work-alikes.

One of the projects whilst in Snowdonia was to develop a low cost single axis solar PV tracker. This uses a single radio control servo to angle a small PV panel directly towards the sun and record the power produced. Nanode 5 has a 3 pin connector which will directly take an R/C servo which is controlled by Digital 4.

Here's a short video showing the tracker working. Following a reset, the servo turns the panel to face east and then it searches in 10 degree steps for the solar power maxima. After completing the 180 degree search it returns to the maxima position - about 39 seconds into this clip. Once a minute (at about 1min 05), it then tracks east by 5 degrees and performs a 1 degree incremental sweep for 10 degrees to see if it can find a better maxima.

We have developed a fair bit of code for Nanode and this is now up on GitHub

The updated pcb artwork is very nearly completed and after checking this weekend will be released to Spirit Electronics so that a batch of 100 bare boards can be manufactured. This will take approximately 2 weeks - so we expect to have Nanode pcbs available for assembly about 23/5/2011.

1 comment:

John Crouchley said...

Hi Ken,
you say
>>Digital 5 Used by Nokia 3310 LCD shield
Which shield is this? - the Nuelectronics shield uses 7,8,9 as well as the SPI bus with 10 as CS.
I would love to see a shield that only uses SPI.