Customized BRB SBD
The BRB Iridium SBD transmitter is frequently customized, usually with small changes to the firmware. The latest version required changes to the hardware as well.
This version is intended to be used on a commercial fishing boat. A DC-DC converter drops the incoming 12-24 V power to a more manageable 5V, which powers a lithium poly battery charger connected to a single cell battery. If main power is lost, a small circuit consisting of a few diodes and transistors will switch over to the battery as a backup. An analog to digital converter reads the battery voltage, and can determine if it is running on main or backup power.
Two sets of inputs monitor engine inputs and are used to collect RPM data. These inputs are connected via optoisolators to protect the electronics from voltage spikes generated by the engines.
SBD packets are sent periodically and contain the GPS position as well as sensor data. Data packets are also collected more frequently and stored in onboard flash memory for download at a later time.
To reduce SBD data usage, packets can be compressed into a binary format more than 50% smaller than plain ASCII. A "home position" can also be entered at the push of a button. SBD packets will be inhibited if the device is 'too close to home'.
The device parameters are set via a USB cable and a terminal emulator such as TeraTerm or Putty. Commands may also be sent "over the air" via the Iridium network if physical access to the device is not practical.
The board measures 65x45 mm. The SBD modem and Iridium/GPS antenna are attached to the back of the board for a total height of 35mm.
More information is available here: https://shop.bigredbee.com/pages/iridium-sbd