* MCU: Freescale KL25z - ARM Cortex M0+ Dev Board

• Programmed with the mbed compiler

* Radio: HopeRF RFM22B

Live Telemetry: Node 'P0'

The gateway node is piggy-backed onto a Raspberry Pi to provide the upload of packets to the API.

A DS18B20 temperature sensor is also attached to provide a temperature reading of the room.

The node code copies the packets that it hears (and its own beacons), to one of the serial ports that is connected to the Pi's UART (/dev/ttyAMA0).

I then run a python script (ukhasnet-upload.py) on the Pi to receive the packets from the node, and upload them over HTTP to the ukhas.net API.

Live Telemetry: Node 'P1'

This node runs off of a 3.7V 2Ah LiPO battery and has 2x 5.5V 200mA solar panels to provide charging. A cheap USB LiPO charger is used to regulate power from the solar panels, and an MCP1703 3.3V regulator on a re-purposed HAB Tracker board is used to provide a stable 3.3V supply to the MCU and Radio.

A DS18B20 is attached and located outside the box to provide a temperature reading. A 2:1 resistor divider also allows measurement and reporting of the current battery voltage.

The solar panels are not proving sufficient to charge the battery with the current weather, so this node is brought inside for a short period to be charged up every few days.

The NiMH AA cells in the bottom are simply to provide weight to stop the box being blown away! The scrunched paper stops the weight from shifting around. The LiPO is the silver and yellow unit under the black regulator board in the center.

* MCU: Freescale KL25z - ARM Cortex M0+ Dev Board

• Programmed with the mbed compiler

* Radio: HopeRF RFM69HW

The second generation uses the newer (and hopefully more reliable) RFM69HW Radio Module.

For this I am in the process of taking Low Power Labs' RFM69 Arduino Lib, stripping it down to just what we need, and putting it into the structure of the existing mbed RF22 Lib.

I have designed a 'shield' PCB to sit on the KL25z dev board to support the RFM69, Lipo Charger and 3.3V Regulator. The PCB also provides an SMA socket for the 868MHz antenna, a standard LiPo socket, headers for a 5-6V solar array, and a microUSB socket for easy desktop charging. 3x footprints for DS18B20 connections are also provided.

Gerbers: GerbLook - Sent off for manufacture!!

BOM:

• 1x RFM69HW FSK Transceiver
• 1x MCP1700 3.3V LDO - Farnell 1296588 - Datasheet
• 1x MAX1555 LiPo Charger - Farnell 1628222 - Datasheet

• 7x 1uF 0805 Capacitors - Farnell 1828830
• 2x 1000uF Reservoir Capacitors - Farnell 1219447
• 3x 100K 0603 Resistors - Farnell 2309107

• 1x Molex MicroUSB - Farnell 1568026
• 1x JST 2mm 2way - Farnell 9492615

TODO:

• Remove 2x Large Reservoir capacitors - not required
• USB Vcc connected to USB Vin on KL25z board - will also charge from KL25z USB sockets.
• Use larger SMA socket footprint - For UK-available parts
• Add jumper to switch off KL25/Radio supply from lipo/charger - allow switching off/isolating lipo charging
  • 40mA Precharge Current for dead lipo was barely enough to power board, let alone charge the Lipo as well.