Bluejay configurator: flash and set up Bluejay ESCs

Bluejay is ESC firmware for the same 8-bit SiLabs EFM8 hardware that BLHeli_S runs on. It started from the BLHeli_S code and added the features modern flight controllers expect: bidirectional DShot, which sends each motor's RPM back to the flight controller, extended DShot telemetry (EDT), DShot 300 and 600, a choice of PWM frequency and user-written startup tunes.

Bidirectional DShot is the main reason. Betaflight's RPM filter needs the motor RPM from every ESC, and stock BLHeli_S does not send it. Flashing Bluejay onto an existing BLHeli_S ESC gives you RPM filtering without buying new ESCs. Once Bluejay is on, turn on Bidirectional DShot and set the motor poles in the Motors tab of the Betaflight configurator, then check that every motor reports RPM.

The ESCs are already wired to the flight controller's motor outputs. Betaflight and INAV can turn those outputs into a serial link to each ESC's bootloader, called the 4-way interface or ESC passthrough. FlySpark asks the flight controller to enter passthrough, then talks to each ESC in turn. While you are in the ESC screen the flight controller pauses its normal MSP link; when you press Done it leaves passthrough and FlySpark reconnects to it.

The ESCs only answer when they have battery power, so connect USB first and then plug in a pack. If the flight controller says it found no ESCs, the battery is usually the reason. Passthrough also needs a digital motor protocol such as DShot or Multishot, and the drone must be disarmed.

Bluejay moved several settings bytes between versions, so a byte that means startup power in one release can mean something else in the next. FlySpark only offers the Bluejay settings whose position and meaning are the same as in BLHeli_S: motor direction, beep strength, beacon strength and beacon delay, plus the startup melody, which has its own fixed place. Every other byte on the settings page is read and written back exactly as it was, so nothing you set elsewhere is lost.

If you need Bluejay's other options, such as startup power limits, temperature protection or brake on stop, set them in a configurator that tracks every Bluejay settings layout, such as esc-configurator.com, and use FlySpark for flashing, direction and tunes. The ESC screen says this in the settings card whenever a Bluejay ESC is connected.

Every BLHeli_S and Bluejay build is made for one hardware layout. The layout name has three parts: a letter for the board design, a letter for the chip (L for EFM8BB1, H for EFM8BB2, X for EFM8BB51) and a dead-time number, for example A_H_15. Bluejay release files add the PWM frequency and version, such as A_H_15_48_v0.21.0.hex.

FlySpark reads the layout from each ESC's settings page and requests exactly that file, so you do not have to work it out. If your four ESCs report two different layouts, the right file is fetched for each. When you pick a .hex from your phone or computer instead, FlySpark compares the file's layout and chip tags with each ESC before writing. A layout mismatch is shown and can be overridden with Flash anyway if you know what you are doing; a chip mismatch is never flashed.

The PWM frequency is how fast the ESC switches the motor phases. In short, lower is more efficient and higher runs smoother and quieter. Bluejay's settings documentation adds that higher frequencies have fewer throttle steps unless PWM dithering is on. FlySpark preselects 48 kHz because it suits most quads. Some pilots choose 24 kHz for efficiency on longer flights and 96 kHz on small, high-KV whoops where smoothness matters more.

Because the frequency is compiled into the file, changing it means flashing again with the other build. That takes about the same time as an update, and your direction and beep settings are kept.

Bluejay plays a melody when it powers up, stored in a 128-byte block next to the settings. FlySpark's melody editor reads the current tune from any Bluejay ESC, lets you type RTTTL ringtone text or tap notes on a keyboard at the length and octave you choose, and draws the result on a piano roll you can preview. Presets include the Bluejay default, rising beeps and a short chirp.

The editor tells you how many of the 128 bytes the tune uses, which notes do not fit and which are outside the ESC's range (roughly D3 to D7). Writing the tune keeps every other setting. Power-cycle the ESCs to hear it. Removing the melody makes Bluejay start silently.