The uAvionix Sentry is a compact, self-contained, battery powered ADS-B receiver that provides information to the ForeFlight application. Data provided includes weather, traffic (other aircraft), and backup attitude indication. It's generally used in civil aircraft whose onboard systems do not posses ADS-B in functionality. Using their proprietary AV-Link protocol, it can communicate with other cockpit panel instruments such as the AV-30 to display traffic, weather, and GPS positioning information. Certain Sentry variants, including the one below, even have a built-in carbon monoxide detection and warning system.
This Sentry was dropped and immediately stopped powering on. It was about to be scrapped, but we decided to take a look at it. The plastic casing separates after four screws are removed. Contained inside is a circuit board with a single 18650 cell adhered (poorly) to the plastic casing by some VHB tape.
We immediately found the problem that was preventing this unit from working. The shock from the drop caused the steel tab on one side of the battery to break in half. The other side was quite weak as well but not broken. The 18650 cell is secured to the board and connected electrically by spot-welded tabs on either side. The board side is just soldered into some large openings. This inexpensive construction causes all the mechanical strain from the mass of the battery to be transferred to the board in the event of a shock. The repair was straightforward. We de-soldered and removed the steel tabs from the board and battery. We then used short lengths of flexible wire to connect the batter directly to the board while allowing for a bit of movement. This should prevent similar issues in the future. The battery is still wedged in between the board and plastic casing, therefore it should not move around very much.
Since we had the unit open, it was worth taking a look at the components on the board. This is the back side, which contains a few notable components. First is a uBlox NEO-M8N GPS receiver and antenna (located directly above). There is also a PING PF007 which is a custom part from uAvionix that is most likely responsible for receiving ADS-B data. Located below that is a Lattice FPGA. Located within the left corner of the gold outline is a sensor package (either altitude/pressure or for the CO sense feature). On the middle of the bottom is the USB-C port and located above that is a micro-SD card slot with a card inserted. This card likely contains the firmware or data logged during the flight.
On the front side of the board are some RGB LEDs for the status indicators, power button, RTC battery, a piezo buzzer, and an ESP32. The ESP32 is an interesting choice for a device designed for use in an aircraft, but it's not a critical instrument or flight control device, so it makes sense. uAvionix uses the ESP32 and similar off-the-shelf devices in their other products such as the skyBeacon. There are some interesting gold-plated antennas integrated into the PCB. The square metal-lidded SMD components are interesting, but were challenging to identify. We suspect they are crystal oscillators.
We have linked some information below if you'd like to learn more about this unit or its components.