Thursday, March 3, 2011

First prototypes!

This is not the finest work that the project deserves but I have my limitations when soldering small pitches by hand. Final prototypes and production runs will be totally outsourced so I'll surely want to mount smaller packages, mainly for the Atmega (QFN instead of TQFP) and the passives (0402 instead of 0603). That should let me reduce the size of the panStamp board too, maybe from DIP28 (0.6 in) to a DIP24 (0.6 in) package.

I really like the DIP format. You can plug it onto a bread board, solder components and wires directly to it or grip probes without having to use a mother board. For this first design, I decided to make all Atmega's ports available from the external pins, including the TOSC ones so I may solder a 32.768 KHz crystal for driving Timer 2 or plug an external MHz crystal when the precision or speed of the internal RC oscillator is not sufficient.

The current version of panStamp can be powered from 2.8 to 3.6 regulated VDC. This is not a tremendous voltage range but I have plans to pair the panStamp with an external NCP1400-based board in order to provide better performance for battery-powered applications. Xmegas are a better choice for this kind of battery-operated situations but Arduino does not support Xtmegas AFAIK. Anyway, even without the NCP1400 regulator the panStamp board can operated from a pair of AA/AAA batteries or a coin cell. Not so bad!

panStamp should run from its internal 8 MHz RC oscillator. That will free the TOSC pins for RTC purposes and save some space on the board too. In those cases where speed is really an issue, an external clock can be connected to the board. Powering the board at 3.3 VDC reduces the crystal choice up to 12 MHz or so according to the datasheet but maybe 3.6 VDC would let us use a 16 MHz crystal, the most common crystal valueused in Arduino designs.. By the moment, my initial tests are showing that the internal 8 MHz oscillator is more than enough for driving the CC1101 chip.

I've fabricated a couple of mother boards with USB interface for programming the stamps and acting as serial gateway. The final version will probably show a pendrive from-factor. At the current stage I just needed some extra space for soldering sensors and connecting probes.

Well, it's time now to start developing a CC1101 library for Arduino. Stay tuned for the next episode.

1 comment:

  1. That should let me reduce the size of the panStamp board too, maybe from DIP28 (0.6 in) to a DIP24 (0.6 in) package.speech recognition software