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Hardware Features
All of the components on the node are behind a TPL5111 chip. This chip turns on power to the whole system on a set interval programmed by a set resistor on the node. Once the task is complete by the node this chip will cut power to the whole system again.
This method has two main advantages. The first is that it acts as a watchdog timer. If the micro were to hang on code execution the timer would eventually time-out and reset the micro. The second is that it also drastically reduces power consumption. The idle consumption of each individual component is irrelevant due to these componants not having power when in sleep.
For more information on the boards power consumption please see the page on Power.
On the Micronode the done line is connected to digital pin 2. When the micro-controller drives this done line high the TPL5111 will cut the power to the system. The power will be restored after the interval has passed. For information on the resistors to set this interval see page 13 on the TPL5111 datasheet.
This ARM based micro-controller is the same one that is found on the new Arduino Zero. Choosing this micro allowed us to make it fully compatible with existing arduino libraries and for it to be programmable via the existing Arduino IDE.
This chip comes with a low of features plus low power sleep modes to save power.
As the node would be power cycled between each reading some non-volatile storage would be required. Ferroelectric RAM is much faster than EEPROM while using less power to read and write to it.
The FRAM contains 2048 bytes of storage. This is useful for storing readings to make up a larger data packet. Which saves power if transmitting less often.
For a guide on a library to store and retrieve data please see the FRAM library.
The RTC allows for more advanced timing and waking. The alarm interrupt output on the RTC is connected to the micro controller. The RTC can be used to wake up the micro when it is in deep sleep modes.
Multiple sensor readings can be stored up with timestamps and then transmitted as one data packet. Reducing the number of transmissions saves a lot of power.
This radio uses LoRa which allows for long range communication. If the data being sent is encoded into the correct format for a LoRaWan packet, the data can be picked up and processed by the things network. This gives a large network of receivers for the data produced by the node.
For information on a library to encode data into a LoRaWan packet please see the LoRa Packet library and for information on transmitting this data packet see the LoRa Sender
There is a RGB LED on the node that can be very useful for debugging. The LED can be set to different colours to indicate the current state of the module.
The pins of the RGB LED are connected to pins 11,12 and 13 for RGB respectively.
For library to easily set the colour of the LED please see the RGB LED Library