Wednesday, 28 August 2013

Mini web ATmega1284P board, V2

(Update: 04/Oct/13.  PCB files are now available from here )


A couple of exciting things today smiley
My Goldilocks reward board turned up. Its a work of art, but I'm exercising great restraint, I'll play with it later...
First board built of my second version of Mega1284P mini-web PCB, here is some pictures...
Fractionally wider than the 1st one and with two regulators. One for 5V, one for 3.3V.
A link is available to run both voltages for max speed processing or just run 3.3V for everything in a low power environment.
A reset button, power led and user led are added in this version. Also solder bridges to bring the 2nd serial port out if the RS485 chip is not fitted.
When using both 5V & 3.3V rails and running Ethernet, some quick measurements of current draw gives a max of about 220mA. Thats before using the SD card.
Feeding the input with 7.5V, the regulators get pretty warm. I figure that with the SD card as well, some kind of heat-sinking will be required for continuous running.
However when using the power-down feature on the Wiz820, the current drops to about 45mA (16Mhz xtal). I have yet to experiment with the different sleep modes to see how low I can get it.
Using the Ethernet power-down feature, I can wake up the Wiznet module, post some data to Thingspeak and then shut it down again. When using it in this manner, the regulators get barely warm.
I'll experiment over the coming week, use the SD card as well and make some more measurements and see how it goes.
The radio is mounted at the rear but this time with the cheap mass produced nRF module footprint, a fraction of the cost of the Sparkfun part.
Almost all the pin locations are on a 0.1" grid so it can be plugged onto stripboard if required. The only things that are not on the 0.1" grid are the SD card and Wiznet module pins.


 with the nRF radio module



The Wiznet module unplugged exposing the micro-SD card socket.


underside











face on