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I2C Sensors
06/13/2015 at 02:56 • 0 commentsThe le1 is a space-limited device, only 16kb. So I am designing the dev board to interface with I2C sensors. Most nodes will take some measurement, temperature say, send it along and go back to sleep. Making a couple calls to the I2C bus takes up very little space, giving plenty of room for the network protocol and other housekeeping functions.
Only using I2C means that the larger versions of the le1 aren't really needed. No need to have a bunch of unused GPIO pins when you are only using SDA and SCL.
I haven't figured out how to deal with most sensor breakout boards coming with pullups already.
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REG711-33
06/13/2015 at 02:47 • 0 commentsI have chosen to power the board through multiple sources; battery, LiPo, and USB. To simplify turning the various inputs to a clean 3.3 volts, I'm using the Texas Instruments REG711 3.3v regulator. I debated using the 1.8 volt regulator, but decided against it to make it simpler to use other sensors.
It remains to be seen if this will allow a battery to be used longer. That's the idea though.
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Johanson Balun
06/13/2015 at 02:43 • 0 commentsI had originally designed the dev board using the datasheet schematic. After doing that, I went to DigiKey and found all the parts. I learned something; RF capacitors and inductors are really expensive. In singles at least. I mean really expensive, upwards of $1.50 for a single capacitor.
Looking around, I saw that a single Johanson balun costs under $1.50, uses less parts, and is just all around a simpler solution.
Looking into it more, it wasn't quite that easy. It turns out that to work with the LE1 QFN24 version, you need 2x 1nH Inductors and a small capacitor.