Thursday, August 18, 2011

New PCB design - V.1.0


The board design goes as expected. The new panStamp PCB design is finished so it's now time to work on the mother boards. PanStick, the USB board where panStamp sits on is closed to completion too. On the other hand, I've started some other developments, most of them aimed to act as proof of concept:

Solar harvester
This board is a milestone in the panStamp project. Finding a good compromise between solar cell, step-up PSU and storage device will bring us the product we are looking for: a mother board for ambient measurements capable to work even under poor light conditions.

Basic energy meter
I want to test the performance of the Atmega at 8MHz in direct AC measurements, including power factor and active/reactive readings.

RGB strip driver board
This is just a toy for controlling RGB strips and creating coloured ambiances.

Ethernet board
A simple way to interface SWAP networks from the IP world without having to use a computer as gateway. This is more or less an extension of the opnode project although I've not decided yet whether this board will go for regular production or not.

Back to the panStamp design, I've not uploaded the KiCad files to the wiki yet since I want to test some prototypes first. Instead, I'm posting here some pictures about the board. The circuit is surely quite definitive as I don't expect to do any major change on it, but the PCB will probably suffer some changes, once I have the opportunity to test the RF performance.

 
Figure 1 : Schematics of the panStamp V.1.0 board
MCU and external pinout

One interesting thing is that the new board will include a three-pin footprint for an external resonator. Using Atmega's internal 8 MHz oscillator will be the default option but sometimes a faster clock may be needed. I'm also searching a 32.768 KHz (RTC) cristal that fits on the 1.3 mm x 3.2 mm footprint. This would let us save a couple of microamps in periodic sleeping applications.

 
Figure 2 : Schematics of the panStamp V.1.0 board
RF front-end

Figure 2: 4-layer panStamp board




3 comments:

  1. For future revisions perhaps you would like to consider Johanson Balun (http://www.ti.com/lit/an/swra250a/swra250a.pdf).
    I recently bought a few ones but I have not found the time to test them.
    I shared some of these baluns with Trax (from elektronica.ba) who was interested in using them in his cc1101 RF modem (http://www.elektronika.ba/629/cc1101-rf-modem-and-250mw-amplifier/)

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  2. Hi Juan!

    Johanson's Balums are quite useful in space-limited designs (ex: Chronos watch). However, panStamps, with their DIP-24 format, have the sufficient place to use balum + filter made by discretes. On the other hand, using discretes lets me reduce the price of each unit and also releases me from having to deal with an additional supplier.

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  3. Thanks for such a knowledgeable article. I really appreciate it and will look forward for some more articles like this in near future.pcb assembly

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