Galileo's sensor modules collect data from a variety of sensor devices, including thermocouples, rate gyros, pressure senders, and physical position sensors, then emit this data on the CAN bus in scheduled message transmissions. Each module gathers several pieces of related data, which simplifies wiring by allowing modules to be placed close by the elements they monitor (such as on the firewall, or near the fuel tanks).
Each module contains either a microcontroller or a MCP25050 CAN I/O expander, depending on the functionality required. The I/O expander is inexpensive and easy to use, and wherever possible I have designed modules around it, but it only provides four 10-bit ADC channels so microcontrollers are used wherever more horsepower is required.
Note that in some cases it may be desirable to deploy more than one of a certain type of module, either for redundancy or to provide additional inputs. For example, a standard Cozy MKIV with a retractable nose gear, speed brake, and canopy lock might only require one Equipment module to detect the positions of these devices. However, if retractable main gear is installed a second module might be used to detect the positions of the two additional gear legs.
Modules:
| Name | Controller | Data Elements | Budget |
| Attitude | Microcontroller | Pitch Roll Yaw Slip | $220 |
| Magnetometer | CAN Expander | 3-axis Heading | $80 |
| Air Data | CAN Expander | Absolute air pressure Dynamic air pressure Outside air temperature Cabin air temperature | $40 |
| Equipment | CAN Expander | Gear position Speed brake/flaps position Canopy lock position Flaps 2, if they exist | $20 |
| GPS | Microcontroller | Lattitude Longitude Altitude Heading Speed Satellites and Signal | $40 |
| Fuel | CAN Expander | Level (x2) Pressure (x2) | $20 |
| Engine Operations | Microcontroller | RPM Mixture EGT CHTs | $40 |
| Engine Cooling | CAN Expander | Coolant Temperature Coolant Pressure Oil Temperature Oil Pressure | $20 |
| Voltage | CAN Expander | Bus Voltage Shunt Voltage (Current) | $20 |
| CDI/Glideslope | CAN Expander | CDI Left CDI Right Shunt Voltage (Current) | $20 |
The budgetary pricing above includes sensors for integrated modules, like the solid-state rate gyro/accelerometer combination, but not for modules where sensors are external, such as position switches, fuel level senders, pressure sensors, etc. In some cases these items may be inexpensive, such as micro switches to detect whether the canopy is locked, while in others they may be pricey, like capacitive fuel level sensors. Nonetheless, these would be purchased whether or not Galileo was deployed, and the builder often has a choice between quality, functionality, and cost, so it's hard to accurately predict their costs.
To keep costs low, some of Galileo's modules are generic sensoSensor modules gather related data elements in a single device. For example, absolute and dynamic air pressure (for airspeed, altimeter, and VSI calculations) are gathered by a single module, typically located in the avionics bay, while engine RPM is gathered by a separate device, typically located on the firewall.Each module is addressed, and the displays provide a configuration routine that allows data elements to be mapped to specific addresses. This allows backup modules to be installed to provide redundancy for critical data elements, such as air pressure. It also allows for the design and deployment of "generic" data collection modules. Device addresses are not assigned a priori based on data types. Instead, the builder assigns each device a unique ID, then configures the displays to tell them which addresses will provide specific data elements.
Each CAN bus message has an address and up to eight data bytes, so each module can supply up to eight data elements to the bus. The following data elements are part of the initial design effort: