The name is inspired by two things I love:
- Pulse Width Modulation (PWM): The heartbeat signal that powers every motor in this drone.
- Beatbox: A personal touch (look at the silkscreen artwork on the top layer).
Pulse is a completely custom flight controller that was created from the ground up. I designed the whole stack myself to truly understand how a drone works, from the low-level motor mixing logic to the physics of the gyroscope, even though it would have been simpler to simply rely on off-the-shelf hardware and Betaflight. The custom PCB designs and the particular STM32 firmware I wrote to make the silicon work are both included in this repository, which acts as documentation for that process.
- MCU: STM32F405RGT6 - Chosen because it's a beast at math and has enough pins for everything.
- IMU: ICM-42688-P - Newer and cleaner noise performance than the old MPU6000.
- Barometer: BMP280 - for altitude hold.
- Gimbal Drivers: 2x DRV8313 - integrated directly on the FC.
- Instead of a heavy separate gimbal controller board, I built the drivers right onto the FC to save weight and space.
- Power System: - Redesigned buck converter using LMR14030SDDAR.
- I initially designed it for 6S (25.2V), but realized I wanted headroom. The new design handles up to 40V input.
- 1kHz Control Loop: A strict real-time scheduler runs the physics engine every 1ms.
- Quad-X Mixing: Takes PID output and mathematically mixes it for the 4 motors using TIM8 (Timer).
- Interrupt driven I/O: The Receiver (UART3) and Telemetry (UART4/5) run in the background via Interrupts, so the main flight loop never "freezes" waiting for data.
- Smart Telemetry: Streams live voltage, angles, and state to a Raspberry Pi companion computer.
I added a USB-C port and the "Holy Trinity" of buttons (BOOT + RESET) to the PCB so I don't need external dongles.
- Plug in USB-C.
- Hold BOOT.
- Click RESET.
- Release BOOT.
- Flash the
.binfile using STM32CubeProgrammer (USB DFU Mode).
| Item | Description | Quantity | Unit Price ($) | Total Price ($) | URL | Running Total ($) |
|---|---|---|---|---|---|---|
| PCBA | PCB | 5 PCB, 2 PCBA | $194.74 | $194.74 | https://jlcpcb.com/ | $194.74 |
| Tactile Switches | Boot and Reset Buttons | 2 | $0.0363 | $0.0726 | https://robu.in/product/ts6610tp-160gf-bxg-022-shou-han-50ma-100m%cf%89-100000-times-12v-160gf-round-button-standing-paste-spst-smd-tactile-switches-rohs/ | $195.35 |
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- Power is hard: My first schematic had a buck converter that would have fried on a 6S battery. Catching that mistake saved the project.
- Routing matters: Moving to 4 layers was scary at first, but it solved all my noise and heat issues.
- Code vs. Reality: Writing the firmware forced me to verify every single pin connection. I found out that "polling" a receiver is too slow, so I had to learn how Interrupts work.