Spark Core v0.2.5

Fixed an issue in the design of the buffer circuit, as highlighted in this thread:

https://community.sparkdevices.com/t/mistake-in-spark-core-eagle-schematics/351/8

Thanks to pulsar (on the Spark community) for identifying this issue!

Spark Core v0.2.4

Spark Core v0.2.4 includes one major change: we added a buffer to the MISO line of the CC3000 because the CC3000 and SPI FLASH module share the same SPI lines.

The CC3000 MISO line is a pull-up line when the CC3000 is not communicating. This means that, if another device is communicating on the same line, its voltages are higher than expected; in our case, the SPI FLASH module was communicating at 3.3V high and 1.4V low (instead of 3.3V and 0V).

The SPI FLASH module seemed to still communicate correctly; we could read, write, and erase without encountering any errors. However, it's possible that issues might develop in the long run or in extreme cases, so we implemented a permanent fix: adding a buffer to the MISO line.

We also made 3V3 and GND fixes opportunistically as we re-routed traces on the board.

Thanks to @ladyada for pointing out this bug!

NOTE: This release has been tagged as a pre-release because a flaw in the buffer design would cause the CC3000 to be incommunicative. So don't use this one :-)

Spark Core v0.2.3

Spark Core v0.2.3 represents three significant improvements:

• Fixed a bug where the diode protecting the USB circuit could be blown if RAW was connected to GND. Fix involved replacing the diode with a beefier diode.
• Significantly changed the layout of the RF circuit to improve performance.
• Changed the load capacitance on the RTC crystal (and therefore its capacitors) in order to improve its performance.

Spark Core v0.2.2

Spark Core v0.2.2 represents only very minor changes to improve manufacturability. These changes include:

• Fixing the power plane to improve its consistency across the board
• Moving vias out from under pads

Aaaaaand that's pretty much it. This is a little itty bitty release.

NOTE: We did not finish producing all of the supplementary files for this release, so take caution when using the gerbers/drawings/etc. This should be considered as a non-production ready release.

Spark Core v0.2.1

The Spark Core v0.2.1 has been completed. This version will go into small scale production with our manufacturing partner, and if no issues are uncovered, will also be the large scale production version of the Spark Core.

Release notes:

• Incorporated DFM feedback from our manufacturing partner. DFM, or Design for Manufacturability, is an important part of the hardware development process where we work with our manufacturer to identify design choices that might cause failures on the manufacturing line. In our case, this included a lot of little tweaks to increase spacing between parts that were particularly close together.
• Switched to a through-hole USB connector. Micro USB connectors can be tricky, because if they're used frequently they can get ripped off the circuit board. This has happened to me quite a few times with my Arduino Pro Micros, and at least one of our beta testers has seen this already. We switched to a through-hole part — which means that it has pins that go through holes in the board, rather than sitting flush on top — which will add mechanical stability to the part.
• Selected final part numbers for mass-produced Core, and changed parts when necessary. Selecting components can be tricky business, because there are a number of factors to consider, including specs, quality, price, and availability. We selected parts for the Core such that it is inexpensive to manufacture in China, but parts are also available in the U.S. for folks who want to build their own boards.

Spark Core v0.2

We've just completed development on Spark Core v0.2. This version can be considered a release candidate for Spark Core v1.0 (the version that will be delivered to Kickstarter backers); we expect to make minor tweaks but keep the overall design the same.

v0.2 includes some significant changes from v0.1, which was the version displayed in our Kickstarter campaign. These changes include:

• Added a uFL connector for an external antenna. This is a stuffing option, meaning that there is one PCB design, but two resulting versions of the Spark Core, depending on which components are "stuffed": one with a chip antenna, and one with a uFL connector.
• Added an RTC crystal for accurate timekeeping.
• Improved RF design. The downside to this particular improvement is that it required making the Core slightly larger; the Core is now 0.1" longer than before (although the corners are kinked, so we really just gave the Core a ba-donka-donk).
• Improved power performance. We have made significant changes to the power regulator, which have some notable trade-offs. We're using a larger power regulator that will be able to handle 500mA of current with proper heat dissipation. This regulator also has a very low dropout voltage (210mV) to improve performance with 3.7V batteries. The downside here is that this power regulator maxes out at 6V, so the Core is no longer spec'ed for 9V or 12V batteries. We were hoping to rate the Core for higher voltages, but there was unfortunately no way to do so within our size constraints; because of the current draw of the Wi-Fi module, an LDO would generate too much heat, and a switching regulator would create noise that could negatively affect the RF performance of the Wi-Fi module.
• An RGB LED for displaying the state of the Core's internet connection. This makes debugging connectivity issues much easier.
• An LED connected in parallel to D7. This is much like the LED attached to pin 13 on the Arduino Uno; it means you can test out the Core with a simple blinking LED (or in this case, an internet-connected LED) without any external parts.

There were some other smaller tweaks and improvements, but that covers everything major. Enjoy!