The hardware team here is starting to get very serious about the Electron. We're aiming to have hardware completely locked down - that's pcbs, designs, exact individual components, everything - by mid-June.
Throughout this process we'll be posting questions and updates here, sharing components chosen, schematics and more. We're hoping to do this in a way that enables open and honest dialogue and feedback!. We hope you'll participate and follow along as we get closer and closer to lockdown.
A Kickstarter campaign, and the comments and questions we get during it, always inspires some internal discussion about existing designs and causes us to look at things differently. That's one of the beautiful things about crowdfunding and open source projects. To start out with we want to introduce conversation about 3 different things we've been thinking about a lot since the campaign closed, and in part because of certain questions we've received. Let's get started:
The Community speaks:
The hardware team has been answering your questions and hearing your call for power. There's a strong desire from the community to power up the Electron for all of your portable applications. We love our community and our ears are always pointed towards those great suggestions! That was a pun from "Bilbo".
Power of Greyskull:
Unlike WiFi, 2G and 3G cellular modules are very power hungry, requiring upto 2A of peak current during transmission. This clearly exceeds USB's limit of 500mA in most cases. When developing on the Electron connected to a computer, care must be taken not to exceed the USB's limit while maintaining uninterrupted power to the cellular module. Most portable devices overcome this by having a battery connected at all times, like mobile phones. For a device like the Electron, it becomes essential to have the flexibility to power it either via the USB, battery or both.
LiPo battery technology is effectively today's Power of Greyskull, and were working out how to add this to the Electron. There will be a complete battery management solution on-board the Electron, ready to seamlessly charge up the LiPo battery from USB or deliver power to the Electron's cellular hardware. Packing this into a small area is definitely a challenge, and we accept!
See that little question mark below? Just wondering what you all prefer for a connector solution here? Many LiPo battery packs come with a 2-pin JST-PH connector installed, but they are not all the same polarity or exact style. We're considering a special connector to ensure everything "just works" for you, and make available matching battery packs. This would also give us flexibility to make everything fit just right. How do you guys feel about this connector? Make it right for the Electron, or go with the JST flow?
Package for the microcontroller
The current design of the Electron uses a STM32F205 microcontroller in a LQFP64 package which just about fits in the footprint. We are now toying with the idea of using wafer level chip package (WLCSP) that is almost 10 times smaller, thus saving us significant real estate on the PCB.
There are couple of design challenges in using this smaller package. WLCSP is generally not environmentally protected like the plastic LQFP counterpart. This can be overcome by adding epoxy top or a tin faraday cage like the cellular module itself. Secondly, the BGA solder pads will require higher tolerances during manufacturing and assembly, both of which can be handled by most of today's board houses.
Antenna selection depends on a number of parameters like gain, size, durability, etc. Some of the more common examples are telescopic, patch, bead, helical or high gain directional antenna. Cellular antennas are a little special since they need to work on multiple frequencies. For a project deployed in the field that is static, such as a weather station, one would choose a directional, high gain antenna. For projects that are mobile and portable, one would choose a PCB patch antenna. We are currently evaluating few of these types to ship along with the Electron. We would love your feedback on which antenna you would most like to see on the Electron.
It's your turn now. What are your thoughts on power, chip package and antenna? If it was up to you what would you suggest? We'll take all your feedback into consideration as we make final decisions.