LoRaSerial Hookup Guide
Nate Introduction
The LoRaSerial radios are simply to use radio modems that transmit over long distances (LoRa is a commonly used portmanteau of Long and Range). LoRaSerial is unique in that it makes LoRa and all the finicky radio configuration bits transparent to the user. Pull the radios out of the box, power them up, and you’ll be transmitting serial back and forth effortlessly.
We have successfully received data over 9.2 miles or 15 km line-of-sight. Your mileage will vary depending on the amount of metal, concrete, and other materials you are trying to transmit through. In general, the larger the antenna the better the range. We include ½ wave dipole antennas that have demonstrated impressive range but may be too large for your application. Any 915MHz antenna with RP-SMA termination will work.
LoRaSerial supports both Point-to-Point as well as Broadcast configurations. P2P is common and uses a transmit then wait-for-acknowledgment packet delivery system. Whereas Broadcast simply broadcasts packets without waiting for or expecting an acknowledgement. A Broadcast setup is very useful in systems where you have one ‘base’ transmitting information to multiple receivers or ‘rovers’ (common with GNSS RTK deployments).
LoRaSerial uses Frequency Hopping Spread Spectrum technology or FHSS for short. This allows any given transmission to be split up between frequencies. As you feed new serial data to the radio both transmitter and receiver will start to hop from one frequency to the next. This prevents transmissions from sitting on one frequency for too long (something called dwell time) and allows these radios to operate legally within the 915/868/433MHz* ISM band.
In the United States 433MHz operation requires a HAM radio license. 433MHz is an open band in most other countries.
LoRaSerial supports AES encryption by default as well as unique network IDs. This means that two radios will share a key and transmit any information using 128-bit AES GCM encryption. This is very strong encryption. Further, each radio is ‘paired’ (when in Point-to-Point mode) with another radio. Any packets received with the incorrect ID are ignored. This feature combined with FHSS
LoRa Serial uses a unique and very easy to use train feature. Each radio has a default Network ID and AES key programmed into it. Changing these keys is as easy as pressing a button! If the train button is pressed for more than 2 seconds the RSSI LEDs will begin to blink. Releasing the train button will put the unit into a ‘cylon’ mode. This indicates that the radio has chosen a new ‘random’ Network ID and AES key, as well as turned its radio down to the lowest power. Next, press and hold the train key on the second radio. Once the RSSI LEDs begin to blink, release the button. The second radio will ping the first radio. The units will then exchange new IDs and keys and immediately hop to the next frequency in the table.
Note that training uses the ‘lowest power’ radio setting. We turn the radios down to prevent any eavesdropper from obtaining the new AES keys. While these ‘new’ keys are themselves encrypted, they are encrypted using the default AES key so one could theoretically back out the new AES keys if they are within ~30ft of the devices when they are being trained. If you’re paranoid, train them with the antennas off inside a Faraday cage.
If two radios need to be paired but cannot be proximally near one another there are AT commands to support the changing of the Network ID and the AES key. If a radio is physically unreachable, a radio can be configured and even trained remotely.
The 915MHz band is used in many countries. By default, the radios will use 902 to 928MHz as allowed per the FCC in the USA. Understanding that some countries (looking at you Australia) have a narrower ISM band, the upper and lower frequencies used by the radio can be modified via AT command. Additionally, we plan to offer 868MHz (Europe) and 433MHz (longer range) based radios shortly.
Note: LoRaSerial radios currently use half-duplex serial. This means only one radio can transmit at a time. LoRaSerial was designed for applications that are predominantly one sided, meaning the base station or the remote device periodically transmits some data, and the base station receives it. This configuration is perfect for a remote weather station to transmit data or a chicken coop that needs to receive periodic commands from the house.