hx-esp32-cam-fpv

Open source digital FPV system based on esp32cam.

Features:

ov2640: 640x360 30fps, 640x480 30fps, 800x456 30fps, 800x600 30fps, 1024x576 12fps, 1280x720 12fps
ov2640 with overclocking: 640x360 40fps, 640x480 40fps, 800x456 40fps
esp32s3 + ov5640: 640x360 50fps, 640x480 40fps, 800x456 50fps, 1024x576 30fps, 1280x720 30fps
up to 1km at 24Mbps, 600m at 36Mbps (line of sight)
latency 90-110ms
bidirectional stream for RC and telemetry 115200 Kbps (for Mavlink etc.)
Displayport MSP OSD
on-board and groundstation video recording

Air unit variants:

esp32cam with ov2640 camera
esp32s3sense with ov2640 camera
esp32s3sense with ov5640 camera (recommended for FPV: has 50fps modes)

Ground station:

Raspberry Pi Zero 2W(recommended) ... Raspberry Pi 4B with rtl8812au(recommended) or AR9271 wifi card. Dual rtl8812au are recommended for FPV.

Original project

esp32-cam-fpv project was originally developed by jeanlemotan https://github.com/jeanlemotan/esp32-cam-fpv (currently seems to be abandoned). Some more work has been done by Ncerzzk https://github.com/Ncerzzk/esp-vtx who also seems to developed custom air unit hardware https://github.com/Ncerzzk/esp-vtx-hardware and continues to work on gs https://github.com/Ncerzzk/esp-vtx-gs-rs.

The goal of this fork is to develop fpv system for small inav-based plane, starting from the prof-of-concept code of jeanlemotan.

Theory

Wifi bandwidth is too small for uncompressed video streaming. ESP32 is too slow for video encoding. MJPEG encoding is done by camera sensor module (ov2640 or ov5640). Camera module continuously scans pixels and encodes rows as JPEG data which is received by ESP32 at 10MHz I2S clock (ESP32) or 20MHz (ESP32S3 + ov5640), written to the SD card (if the DVR is enabled), FEC encoded and passed directly to Wifi.

The esp32-camera component https://github.com/RomanLut/esp32-camera has been modified to send the data as it's received from the DMA instead of frame-by-frame basis. This decreases latency quite significantly (10-20 ms) and reduces the need to allocate full frames in PSRAM. Ncerzzk even removed PSRAM on his board. While frame is received from the camera, it is already in flight to GS.

The wifi data is sent using packet injection which is possible on ESP32 platform. Data is sent with forward error correction encoding (FEC) which allows GS to recover lost packets. No acknowlegements are sent from GS and no retransmissions are done by air unit.

The air unit can also record the video straight from the camera to the SD card. There is a significant buffering when writing to SD (3MB at the moment) to work around the very regular slowdowns of SD cards. The video quality of air unit recording is the same as on GS (no recompression is done).

The size of JPEG images vary a lot depending on number of details in the view. Adaptive JPEG compression level adjustment is implemented. Compression is adjusted to achieve frame sizes which fit into available bandwidth.

The receiver is a Raspberry PI Zero 2W ... Pi4 with Realtek 8812au(recommended) or AR9271 adapter in monitor mode. Two wifi adapters may work as diversity receivers if required.

8812au with LNA is recommended, while PA is not that important. Range is limited by ESP32 maximum output power of 100mW (20dB).

The JPEG decoding is done with turbojpeg to lower latency and - based on the resolution - can take between 1 and 7 milliseconds.

It's then uploaded to texture and shown on screen.

OSD is drawn on top of the video with OpenGL ES.

The link is bi-directional so the ground station can send data to the air unit. At the moment it sends camera and wifi configuration and bi-directional stream for telemetry (FEC encoded).

Here is a video shot at 30 FPS at 800x456 with ov2640 sensor with 120 degeee lens:

V030_009.2.mp4

Is it worth building?

Do not expect a lot from this system. It all starts with a cheap camera (ov2640) comparable to 2005 smartphone cameras. With such camera you have to accept noisy sensor, bad brightness/contrast against light, distorted colors, low light sensitivity, vignetting from cheap lenses, bad focus on corners, high jpeg compression artefacts etc.

Secondly, esp32 is not capable of video encoding, which means that video stream is sent as a sequence of JPEG images, wasting bitrate which could be used to represent more details otherwise.

Due to low resolution, esp32-cam-fpv competes with cheap analog 5.8 AIO camera, not with other digital fpv systems.

Compared to analog AIO camera, hx-esp32-cam-fpv offers for the same price:

air unit and ground station video recording
digital OSD
(Mavlink) telemetry and RC
telemetry logging
absence of analog noise on image

The downside is high JPEG compression, no WDR, distorted colors, low light sensitivity(ov2640), varying quality of sensor and lenses, frame droping.

For FPV flight with glasses, a setup with esp32s3sense + ov5640 with dual Wifi adapters is recommended. Frame droping is not comfortable for FPV. esp32s3sense + ov5640 offers 50Fps modes while dual adapters offer lower packet loss/frame loss ratio.

hx-esp32-cam-fpv definitely looses againg all commercially available digital FPV systems in terms of image quality.

The benefits over other open-source systems (OpenHD/Ruby/OpenIPC) are:

minimal air unit price
tiny air unit size (esp32s3sense)
low power consumption (less then 300mA at 5V)
ground station hardware used for other fpv systems can be reused for hx-esp32cam-fpv project, just with different SD card inserted

Building

Note

Please use release branch. master can be unstable.

Air Unit

esp32cam

Flashing esp32cam firmware: /doc/flashing_esp32_cam.md

esp32cam does not have enough free pins. Two configurations are available currently. Configuration is selected in main.h before building air unit firmware.

Air Unit Variant 1: Displayport MSP OSD + REC button

Air Unit Variant 2: Displayport MSP OSD + Mavlink

Both internal red LED and flash LED are used for indication:

solid - not recording
blinking 1Hz - recording
blinking 3Hz - OTA update mode.

Replace flash LED with small indication LED (Blue LED + 100 Ohm resistor), or remove, or paint with black marker:

REC button is used to start/stop air unit recording. Hold REC button on powerup to enter OTA (over the air update) mode.

With pcb antenna, 50m transmission distance can barely be achieved. A jumper has to be soldered to use external antena: https://www.youtube.com/watch?v=aBTZuvg5sM8

esp32s3sense

Flashing esp32s3sense firmware: /doc/flashing_esp32s3sense.md

Air Unit Variant 3: esp32s3sense + ov2640

STL files for 3D Printing on Thingiverse: https://www.thingiverse.com/thing:6624598

Module comes with moderate flexible antenna which should be replaced with 2dBi dipole to maximize range.

Internal yellow LED conflicts with SD card and thus can not be used for indication. External LED should be soldered to pin D0.

Existing Boot button is used to start/stop air unit recording.

A jumper should be soldered on J3 to enable SD card usage (somehow it works without it, but is required for stable operation).

Air Unit Variant 4: esp32s3sense + ov5640

ov5640 on esp32s3sense camera offers 640x360 50fps, 640x480 40fps, 800x456 50fps, 1024x576 30fps and 1280x720 30fps modes, less noisy sensor, much beter colors and contrast, good performance against sunlight.

es32s3sense boards are sold with ov2640 camera which can be easily replaced with ov5640 purchased separately.

800x456 30fps 26Mbit with ov5640 camera 160 degree lens:

V032_021.mp4

STL files for 3D Printing 14mm lens shell on Thingiverse: https://www.thingiverse.com/thing:6646566

Current consumption

Both esp32cam and esp32s3sense consume less then 300mA. Flash LED on esp32cam board consumes 30mA itself.

Ground Station

Preparing SD Card for GS from pre-built image: /doc/building_gs_image.md

Or building GS image : /doc/building_gs_image.md

STL files for 3D printing enclosure on Thingiverse: https://www.thingiverse.com/thing:6624580

Ground Station Variant 1: Single rtl8812au

Single wifi card is Ok for GS with LCD monitor.

Ground Station Variant 2: Dual rtl8812au

Dual wifi cards variant benefit less frame dropping.

A small USB 2.0 hub board is used to connect two wifi cards and add two USB port sockets.

Small rtl8812au cards are used. AV output is reserved for future use.

Note that red/black antenas are not recommented unless all you want is to look cool :) These are 2dbi wideband antenas. A pair of 2.4Ghz BetaFPS Moxons with 90 degree adapters are recommended instead.

Displayport MSP OSD

Configure Displayport MSP OSD 115200, Avatar in INav/Betaflight/Ardupilot.

A number of OSD fonts are included. User fonts can be placed in /gs/assets/osd_fonts/ - 24 pixels wide png format.

osd.mp4

Mavlink

Can be used for RC and for downlink telemetry. Setup 115200 UART.

This is transparent bidirectional stream sent with FEC encoding (Groun2Air: k=2 n=3, Air2Ground: Same as video stream, k=6 n=12 by default).

Camera OSD Elements

From left to right:

RSSI in Dbm
Average wifi queue usage. Should be below 50%. Look for free wifi channel if it turns red constantly
actual MJPEG stream bandwidth in Mbps (without FEC encoding). Wifi stream bandwwith = MJPEG stream bandwidth * FEC_n / FEC_k
resolution
FPS
!NO PING! Indicates that air unit does not receive GS packets (configuration packets, uplink Mavlink)
AIR Air unit is recording video to SD card
GS GS is recording video to SD card
!SD SLOW! SD card on AIR unit is too slow to record video, frames are skipped

OSD Menu

OSD Menu can be navigated with GPIO Joystick, keyboard or mouse.

Key	Function
Joystick Center, Enter, Right Click	Open OSD menu
Joystick Right, Air REC, GS REC,Esc, Right Click, R, G	Close OSD Menu
Joystick Center, Joytsick Right, Enter, Left Click	Select menu item
Joystick Up, Arrow Up	Select previous menu item
Joystick Down, Arrow Down	Select next menu item
Joystick Left, Arrow Left, ESC	Exit to previous menu

GPIO Joystick button mapping

GPIO Joystick and buttons are mapped to keys.

Key	Function
Joystick Center	Enter
Joystick Left	Arrow Left
Joystick Right	Arrow Right
Joystick Up	Arrow Up
Joystick Down	Arrow Down
AIR REC	r
GROUND REC	g

Other keys

Key	Function
Space	Exit application
ESC	Close OSD menu or exit application
d	Open Development UI

Considerations

Resolution

OV2640

esp32cam and esp32s3sence boards come with the OV2640 sensor by default.

The sweet spot settings for this camera seems to be 800x600 resolution with JPEG compression level in range 8…63 (lower is better quality). 30 fps is achieved. Additionaly, custom 16:9 modes 640x360 and 800x456 are implemented. Personally I like 800x456 because 16:9 looks more "digital" :)

Another options are 640x480 and 640x360, which can have better JPEG compression level set per frame, but luck pixel details and thus do not benefit over 800x456.

Any resolution lower then 640x360, despite high frame rate (60fps with 320x240), is useless in my opinion due to luck of details.

ov2640 can capture 1280x720 at 13 FPS. Image looks Ok on 7" screen, but FPS is definitely is lower then acceptable level for FPV.

It is possible to overclock ov2640 sensor in Camera Settings to enable 40Fps in 640x360, 640x480 and 800x456 modes, however it is not garantied to work. If it does not work - try with another sensor.

ov2640 is Ok for day but has much worse light sensitivity and dynamic range compared to ov5640 in the evening. This and next video are made in almost the same light conditions:

800x456 30fps 26Mbit with ov2640 camera 120 degree lens:

V042_008.mp4

OV5640

OV5640 supports the same resolutions and offers the same FPS thanks to binning support, but also have much better light sensivity, brightness and contrast. It also has higher pixel rate and supports 1280x720 30fps (which can be received by esp32s3 thanks to 2x maximum DMA speed).

800x456 image looks much better on ov5640 compared to ov2640 thanks to highger sensor quality and less noise.

However, 1280x720 30fps requres too high bandwidth, so system has to set high compression levels which elliminates detais. Overall, 1024x576 30fps looks better. Both modes require 36Mbps+ wifi rate to provide benefits over 800x456.

It is possible to enable 50Fps 640x360 and 800x456 modes is Camera Settings. These modes are the best choise for FPV. Unfortunatelly, camera seems to distort colors in low light conditions in these modes (flying in the evening).

While ov5640 can do 50Fps in higher resolution modes, it does not make a sense to use them because higher FPS requires too high bandwidth for MJPEG stream.

Note: ov5640 does not support vertical image flip.

800x456 30fps 26Mbit with ov5640 camera 160 degree lens:

V037_002.mp4

Lens

Both esp32cam and esp32s3sense come with narrow lens which definitely should be replaced with wide angle 120 or 160 lens to be used on UAV.

Note that there are sensors with slightly different lens diameter. Two sensors on the left are compatible; the one on the right is not.

Note that "night version" sensor does not have IR filter and shows distorted colors under sunlight (buy a proper sensor!).

Wifi channel

Default wifi channel is set to 7. 3…7 seems to be the best setting, because antennas are tuned for the middle range. F.e. in my experiments, channel 11 barely works with AR9271 and esp32s3sense stock antenna. In the crowded wifi environment, best channel is the one not used by other devices. System may not be able to push frames on busy channel at all (high wifi queue usage will be shown on OSD).

Wifi rate

24Mbps seems to be a sweet spot which provides high bandwidth and range.

Lowering bandwidth to 12Mbps seems to not provide any range improvement; reception still drops at -83dB.

Increasing bandwidth to 36Mbps allows to send less compressed frames, but decreases range to 600m. 36Mbps bandwidth is not fully used because practical maximum ESP32 bandwidth seems to be 2.3 Mb/sec. Maximum SD write speed 1.2Mb/sec (esp32) and 1.6Mb/sec (esp32s3) should also be considered here for the air unit DVR.

Wifi interferrence

Wifi channel is shared beetween multiple clients. In crowded area, bandwith can be significanly lower then expected. While tested on table at home, hx-esp32-cam-fpv can show ~5FPS due to low bandwidth and high packet loss; this is normal.

Note than UAV in the air will sense carrier of all Wifi routers around and share wifi channel bandwidth with them (See Carrier-sense multiple access with collision avoidance (CSMA/CA) )

DVR

Class 10 SD Card is required for the air unit. Maximum supported size is 32MB. Should be formatted to FAT32. The quality of recording is the same on air and ground; no recompression is done (obviously, GS recording does not contain lost frames).

ESP32 can work with SD card in 4bit and 1bit mode. 1bit mode is chosen to free few pins. 4bit mode seems to provide little benefit (30% faster with 4 bit). Overal, 1.9Mb/sec in 1 bit mode is more then Wifi can transfer, for SD writing speed is not a limiting factor for now.

Adaptive compression

With the same JPEG compression level the size of a frame can vary a lot depending on scenery. A lot means order of 5 or more. Adaptive compression is implemented to achieve best possible image quality.

For ov2640 sensor, compression level can be set in range 1..63 (lower is better quality). However ov2640 can return broken frames or crash with compression levels lower then 8. Also, decreasing compression level below 8 increases frame size but does not increase image quality much due to bad sensor quality itself. System uses range 8...63.

Frame data flows throught a number of queues, which can easily be overloaded due to small RAM size on ESP32, see profiling.

Air unit calculates 3 coefficients which are used to adjust compression quality, where 8 is minumum compressoin level and each coefficient can increase it up to 63.

Theoretical maximum bandwidth of current Wifi rate is multipled by 0.5 (50%), divided by FEC redundancy (/FEC_n * FEC_k) and divided by FPS. The result is target frame size.

Additionally, compression level is limited by maximum SD write speed when air unit DVR is enabled; it is 1.9MB/sec frame data for ESP32/esp32s3sense.

Additionally, frame size is decreased if Wifi output queue grows (Wifi channel is shared between clients; practical bandwidth can be much lower then expected). This is the most limiting factor.

Adaptive compression is key component of hx-esp32-cam-fpv. Without adaptive compression, compression level have to be set to so low quality, that system became unusable.

FEC

Frames are sent using Forward error correction encoding. Currently FEC is set to k=6, n=12 which means that bandwidth is doubled but any 6 of 12 packets in block can be lost, and frame will still be recovered. It can be changed to 6/8 or 6/10 in OSD menu.

FEC is set to such high redundancy because lost frame at 30 fps looks very bad, even worse then overal image quality decrease caused by wasted bandwidth.

Wifi card

This RTL8812au card is recommended for the project:

It can do high power output which is not important for esp32cam-fpv, but it comes with good 5dBi antenas which is the best purchase in summary.

Other cards should also work but not tested.

AR9271 should also work but not tested. RTL8812au has antena diversity and thus is recommended over AR9271.

Antenas

This 2.4Ghz antena seems to be the best choice for the UAV because it is flexible and can be mouted on the wing using part of cable tie or toothpick:

Various PCB antenas for 2.4Ghz can be considered (not tested):

The best choice for GS is pair of 5dBi dipoles or 5dbi dipole + BetaFPV Moxon Antenna.

It is important that all antenas should be mounded VERTICALLY.

esp32cam PCB antena can not provide range more then a few metters.

Note: esp32cam board requires soldering resistor to use external antena: https://www.youtube.com/watch?v=aBTZuvg5sM8

Do not power wifi card or ESP32 without antena attached; it can damage output amplifier.

Dual Wifi Adapters

hx-esp32-cam-fpv supports dual Wifi adapters to decrease packet loss ratio. Default launch script will launch GS in dual adapters mode if wlan1 and wlan2 are found in the system.

Range

2dbi dipole on plane, 5dbi dipoles on GS: 1.2km at 24Mbps, 600m at 36Mbps (line of sight, away from wifi routers). Will drop to few metters with walls/trees on the way.

2dbi dipole on plane, 5dbi dipole + BetaFPV Moxon Antenna on GS: 2km at 24Mbps, 900m at 36Mbps.

Range is limited by ESP32 output power (100mW 20dB) and highly depends on antena type and quality.

Tested on inav microplane: https://www.youtube.com/watch?v=GYB-UckucRA

Drivers

I am still searching for the best RTL8812au drivers for this project.

There are seems to be few choises:

Works fine on RPI0 2W, does not work on RPI4: https://github.com/morrownr/8812au-20210629
Works fine on RPI0 2W, does not work on RPI4: https://github.com/morrownr/8812au-20210820
Seems to work but does not report RSSI: https://github.com/svpcom/rtl8812au/tree/v5.2.20
Seems to work but RSSI seems to be reported 2x higher then real sometimes: https://github.com/svpcom/rtl8812au/tree/v5.2.20-rssi-fix-but-sometimes-crash
Does not work: https://github.com/aircrack-ng/rtl8812au

Proper drivers for AR8271 are included in OS image already.

Note that some optimizations important for other open source digital FPV systems are not important for hx-esp32-cam-fpv. Wifi card is not used on air unit, so high output power and and high-bandwidth packet injection are not important.

Latency

Latency is in range 90-110ms for all resolutions at 30 and 50fps. This is still to be double checked because esp32 simply does not have memory to buffer more then 30ms. From technological side, this system is close to HD Zero which do not need to wait for the full frame from camera to start transmission, expected latency should be in range 40-80ms.

Raspberry Pi Zero 2W GS with 60Hz TV:

Unsuccessfull attempts

Attempt to use internal Rapsberry Pi Wifi card in monitor mode

NEXMON drivers https://github.com/seemoo-lab/nexmon offer monitor mode and packet injection for internal wifi card of Raspberry Pi. Original idea was to build extremely cheap ground station based on Raspberry Pi with internal antena replaced by dipole.

Unfortunatelly these attempts were unsuccessfull.

NEXMON drivers do support monitor mode and are used in Kali Linux builds for Rapsberry Pi. Unfortunatelly, to many packets are missed while listening for high-bandwidth stream. Packet injection barely works; few packets can be sent which might be enough for wifi deauth, but not for sending data stream. Attempts to use packet injection crash the driver. Attempts to send packets lead to lossing 70% of incoming packets. Packet injection is disabled in the last builds of Kali Linux.

Even with external 2dBi dipole soldered properly, sensitivity is very bad. RSSI shows values 20dB less compared to rtl8812au card. In experimental single directional fpv system I was able to achieve ~20m transmission distance.

Additionally, there is a bug in the driver: if wifi hotspot which was associated last time is not available on boot, driver crashes on boot and wifi adapter is not available (a surpise on the field!).

Lesons learned:

a wifi card with a good sensitivity and proper drivers with monitor mode and packet injection support is a key factor for successfull open source digital FPV system. So far only rtl8812au matches these criterias and is recommended choice.
you should aim for the best reception sensitivity possible on ground; GS should not be cheap. Air unit should be cheap - it can crash or fly away; GS is not.

Using sensors with long flex cables

esp32cam can not rotate image and thus should be mounted vertically (vertical image flip is possible). Such form factor is not the best for a small plane.

Sensors can be bought with flex cables of various length.

Unfortunatelly attempt to use sensor with long flex cable was unsuccessfull. Flex cable wires cary high frequency (10Mhz) digital signals which produce a lot of RF noise. GPS sensor mounted in less then 7cm from esp32cam was jammed completely. Micro plane does not have a lot of space to separate GPS sensor from esp32cam. Even moved to the end of the wing (15cm away from esp32cam) it still barely found any satellites. esp32cam and flex cable shielding improved situation a little bit, but not enough to trust GPS sensor and try a range testing.

esp32cam with long flex cable has been replaced with compact esp32s3sense board.

Development

See development.md

FAQ

Can original Raspberry Pi Zero W be used as GS?

No, RPI0W does not have enough performance to decode 800x600 MJPEG stream with it's CPU.
Do I need to pair Air unit and GS?

Currently there is no pairing procedure; GS will receive signal from any air unit. As project is in early development state, it is assumed that there are single Air Unit and single GS in the area. If you ever try to test multiple systems, make sure channels are separated at least by 3, so that GS will not hear other air unit.
What if packet lost and FEC can not recover?

Then the whole frame is lost. That's why FEC is set to high redundancy by default.

Name		Name	Last commit message	Last commit date
Latest commit History 550 Commits
air_firmware_esp32cam		air_firmware_esp32cam
air_firmware_esp32s3sense		air_firmware_esp32s3sense
air_firmware_esp32s3sense_ov5640		air_firmware_esp32s3sense_ov5640
components		components
doc		doc
gs		gs
pi_button_to_kbd		pi_button_to_kbd
scripts		scripts
.gitignore		.gitignore
.gitmodules		.gitmodules
LICENSE		LICENSE
README.md		README.md

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