Thursday, February 04, 2016

WiNode 5 Update

Two weeks ago, I posted about an update to the WiNode, well here's that long awaited update - now that I have finished the pcb layout and submitted it for manufacture.

The board has had some radical design changes since the first conceptual design - and hopefully I have got a very flexible platform for control and datalogging applications.

In it's original form, the layout proved a little too complex for the size of board available - which meant that it was a real pain to route.  So I tried dropping tracksizes first from 10 thou to 8 thou and then from 8 thou to 6 thou.  I then realised that it was still going to be a routing nightmare, so I came up with a Plan B, which was to ditch some of the more complex functions and come up with a good all round ATmega1284 board.

So I retained the RFM69 wireless module and the microSD card, the RTC, and 32K battery backed SRAM but unfortunately the dual H-bridge just has to wait for the next bus.  This means that the ATmega1284 design will not be held up waiting to get a very tight route done.

A Slimmed Down WiNode 5 Board - initial component placement.
I managed to spend most of my free time in the evenings and weekends of the last couple of weeks fighting the EagleCAD autorouter.  In the end I decided that the pcb was just too hard to route with the available tool and algortithms, so I decided that there was only one final solution - and to route it by hand.

Latest Update - February 4th 2016

So here is the latest design, still a 50mm square board with all if the ATmega1284 pins brought out to a standard header format.  It can still connect to two of the Open Inverter power boards, which was the original design brief.

There is also a footprint towards the top of the pcb bsed on the X-Bee, which will accept any plug in wireless module on a carrier pcb. In addition, you may notice the outline of a 40 pin DIL socket. This will allow the DIL version of the ATmega1284P to be plugged into a turned pin socket.

After the culling of the Real Time Clock, the 32K SRAM and the dual H-bridge there has been a partial reprieve  - the RTC and SRAM have been re-instated, as has the boost regulator - which allows the board to run off a lithium cell, or even a single 1.5V alkaline cell.

Earlier in the week I wrote about the CH340 USB to serial converter IC. I have included this and a mini-USB B connector - located in the top right corner of the pcb.  This means that the board will run from multiple power sources for maximum flexibility of applications.

The almost final design after 12 hours overnight session of hand-routing!
Job Done!

After some serious burning of the midnight oil, I pushed the remaining tracks into a layout that I (and the EagleCAD DRC) was happy with (see below) and the Gerbers have been sent off to Ragworm - my local pcb supplier.

This is probably the last 8-bit/AVR board that I will do, as it kind of creates the platform that I wanted some years ago.  The extra 16K of RAM on the ATmega1284 will make it useful for bigger, more demanding applications, and the ability to accept wireless and WiFi modules from a variety of sources should make it useful - for example as an RFM69 to ESP8266 bridge.  The uSD card for datalogging and the RTC for turning things on at given times of day have it destined for all my old favourite central heating controller projects - and within a few weeks I should have a relay shield laid out for it.

The board also has been designed to be compatible with the EVITA graphics engine I designed over Christmas - and that has the means to provide high resolution colourful graphics on a big screen - and I must admit that I'm looking forwards to some big, bold colourful chunky graphics and some neo-retro computing projects.   The ATmega1284 is compatible with GameDuino2 - and so can leverage off of that graphics library. The 2 board stack of WiNode plus EVITA will make a great little retro platform - with PS/2 keyboard and mouse interfaces and the means to accept a Wii Nunchuck controller too!

Final Design Specification

ATmega1284P  with 128K Flash and 16K SRAM - either SMT package or 40 pin DIL package.
microSD card socket on underside of pcb
32Kbytes battery backed SPI SRAM (Microchip 23K256)
Real Time Clock / Alarm / NV RAM  (Microchip MCP79410)

Hope RF RFM69 low power wireless module (433 or 868MHz)
Socket to accept ESP8266-01 WiFi module
Socket to accept X-Bee or any pin compatible device

CH340 USB-serial adaptor - connection via mini B USB
FTDI standard cable connector for debug/programming
Reset switch, and RTS automatic reset when programming from Arduino IDE.

Lithium Polymer battery support
Boost regulator ((Microchip MCP1640) boost from 1V to 5V for LiPo or battery operation
250mA 3V3 linear regulator
Battery temperature and voltage monitoring via on-chip ADC

Extended "Arduino" style expansion headers  with 6 extra GPIO pins
Mini-application headers - 2 off, with 5V, 0V.  2x digital 2x ADC  and 2x PWM outputs
ATmega ICSP programming header 2x3 way
Standard 50mm x50mm 2 layer pcb format with 2 diagonally opposite M3 mounting holes.

Final Design as sent off to Ragworm - my local PCB Supplier

Two weeks later,  I receive 25 boards from my local supplier

The prototype WiNode 5 board prior to assembly.


No comments: