SENT (SAE J2716) USB Converter — SENTToUSB

Open source USB dongle that decodes SAE J2716 / ISO 21097 SENT automotive sensors. Auto-learns tick period, nibble count and CRC mode. Plug-and-play virtual COM port on Windows, Linux and macOS — no proprietary drivers.

USB CDC (Virtual COM Port) adapter for SAE J2716 / ISO 21097 SENT sensors. Decodes 4-, 6- and 8-nibble frames with both DATA_ONLY and STATUS_AND_DATA CRC modes, supports CRC seeds 0x03 (SAE APR2016) and 0x05 (legacy / GM), and includes a TX mode for synthesizing SENT frames to bench-test ECUs. Talks to the host using the SLCAN text protocol over any serial terminal. SENT protocol implementation: open-sent-c.

A commercial SENT analyzer from an automotive tool vendor typically costs hundreds to thousands of euros. This one is around $23 on Tindie.

Where to buy

Where	Region	Link
Tindie	Worldwide	https://www.tindie.com/products/lll7/sent-j2716-usb-converter/
Lectronz	EU	https://lectronz.com/stores/ucandevices
Elty	Poland / EU	https://elty.pl/
Kamami	Poland / EU	https://kamami.pl/

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Hardware

MCU	STM32F042G4UX (UFQFPN28, 48 MHz HSI48, no crystal)
PA2	SENT RX — TIM2 CH3 input capture, internal pull-up
PB0	SENT TX — TIM3 CH3 output compare (toggle, AF1), DMA-driven
USB	Full-speed CDC (Virtual COM Port, no driver needed on Win10+)

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How RX works

Sensor ──SENT signal──► PA2 (TIM2 CH3, RISING edge capture)  [RX]
                              │
                    ISR: timestamp stored in RX HAL ring buffer
                              │
                    Main loop: bridge decodes batch of 10 edges
                              │
                    SLCAN 't' frame → USB → host

1. Host sends O\r — bridge enters RX mode.
2. Every RISING edge on PA2 triggers the TIM2 CH3 capture ISR, which records the raw 16-bit counter value. A separate overflow ISR extends timestamps across the 16-bit rollover (~1.4 ms at 48 MHz).
3. SentApp_Process() (main loop) polls the RX HAL for complete batches of 10 edges: sync + status + 6 data nibbles + CRC + leading edge of next interval.
4. The bridge converts timestamps to µs intervals, extracts nibbles, validates CRC, and produces a CAN frame.
5. The frame is serialised as t<ID><DLC><data>\r and flushed to USB.

Default config (MLX90377): 3 µs/tick, 6 nibbles, DATA_ONLY CRC, seed 0x03, output CAN ID 0x510.

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How TX works

Host ──SLCAN 't' frame──► USB CDC RX callback (ISR context)
                              │
                    bridge → TX HAL (pre-expands frame into toggle array)
                    tim3_dma_start(): arm DMA and start TIM3 if idle
                              │
              TIM3 CH3 OC toggle (AF1 on PB0) fires at CCR3=1 each period:
                First toggle → pin LOW (SENT active-LOW pulse start)
                Subsequent toggles alternate LOW/HIGH per interval
              DMA1_Ch3 reloads TIM3→ARR from pre-computed buffer on each update
              Final DMA TC → TIM3 update ISR → stop timer, pin forced HIGH (idle)

• TIM3 runs at 48 MHz with no prescaler. ARR values are pre-computed (ticks × cycles_per_tick − 1) and stored in a DMA buffer. DMA1_Channel3 reloads TIM3→ARR from that buffer on every update event, so the ISR is only needed for the single end-of-frame cleanup.
• Default 1 tick = 3 µs (ARR = 143 per tick); the host can change the TX tick period at runtime (see SLCAN SET_TX_TICK below).
• Each SENT interval = low_ticks active-LOW pulse (5 ticks, SAE J2716 minimum) + rest for (N − 5) ticks.
• The bridge builds the full interval sequence (sync 56T + status + nibbles + CRC + 12T pause) and the DMA drains it without any per-interval ISR involvement.

Switch to TX mode and send one frame:

O\r                       open SLCAN channel
t600102\r                 start TX mode
t52050100123456\r         transmit: status=1, nibbles [1,2,3,4,5,6]

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SLCAN quick reference

Command	Effect
O\r	Open — start SENT RX
C\r	Close — stop
V\r / v\r	Hardware / firmware version
N\r	Serial number (unique per MCU, XOR-fold of 96-bit UID)
F\r	Status flags
t<ID><DLC><data>\r	Send CAN frame

Control frames (CAN ID 0x600):

data[0]	DLC	Action
01	1	Start RX
02	1	Start TX
03	1	Stop
04	1	Learn tick period / nibble count / CRC mode from live signal
05	3	Set TX tick period: data[1..2] = tick_x10_us (little-endian, 0.1 µs units; valid range 20–900, i.e. 2.0–90.0 µs)

Example — set TX tick to 5.0 µs (tick_x10_us = 50 = 0x0032):

t60030532 00\r  →  t6003053200\r

TX data frame (CAN ID 0x520):

t52050100123456\r
      ↑↑ ↑
      ││ └─ status byte then data nibbles packed (status=0x01, nibbles=0x00,0x12,0x34,0x56)
      │└─── DLC = 5
      └──── CAN ID 0x520

Decoded RX frame (device → host, default CAN ID 0x510):

t5103AABBCC\r    DLC=3, 3 bytes = 6 nibbles packed high-nibble-first

When a slow-channel message completes, the same 0x510 frame is extended to DLC=7. The fast-channel bytes remain first, so old viewers can keep reading the angle:

byte 0..2  fast channel nibbles, unchanged for MLX90377 H.4
byte 3     slow flags: bit0=new slow message, bit1=enhanced, bit2=16-bit ESM
byte 4     slow message ID
byte 5..6  slow data, little-endian

The slow decoder supports SAE J2716 Short Serial Message and Enhanced Serial Message. MLX90377 defaults to ESM with 12-bit data and 8-bit ID. Slow-channel CRC is validated inside open-sent-c; only validated messages are forwarded.

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Python scripts

Script	Purpose
sent_viewer.py	General SLCAN monitor GUI with TX panel and Learn mode
mlx_viewer.py	MLX90377-specific GUI: angle dial + live history plot of angle & magnetic field
sent_test.py	CLI — open port, apply config, print received frames for N seconds
check_rx.py	Loopback sanity check: pings COM8 (TX), listens on COM9 (RX)
tx_signal.py	Continuous TX every 10 ms for logic-analyzer capture on PA4
verify_sent.py	Logic2 automation: capture PA4 signal and cross-check with USB output

Requirements

pip install pyserial

verify_sent.py additionally needs pip install saleae and Logic2 running with the automation API enabled (port 10430).

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Integration Testing

A pytest suite (test_sent_integration.py) drives two SENTToUSB dongles against each other to verify the full TX → wire → RX loop.

Hardware setup

• TX dongle on COM15, RX dongle on COM20 (override at the top of TestSENTIntegration in test_sent_integration.py).
• Wire PB0 of the TX dongle → PA2 of the RX dongle plus a common ground. Without that physical link the data-path tests will report "No 0x510 frames received".

Coverage (18 cases, ~60–90 s)

• Connectivity: V/N/F queries, RX & TX mode entry
• TX → RX frames at 4 tick periods (3, 6, 9, 12 µs)
• 10-frame back-to-back sequence
• Quiet-channel listen (no TX driver)
• Per-tick persistence across multiple frames

Each tick test first sends a 0x001 config frame to the RX device so the bridge can derive a tick-appropriate sync_min_us threshold — the firmware default (100 µs, calibrated for 3 µs ticks) is otherwise fooled by long data nibbles at higher tick periods.

Run

pip install -r test_requirements.txt   # pytest>=7, pyserial>=3.5
python diagnostic.py                   # sanity-check both ports
python -m pytest test_sent_integration.py -v -s

run_tests.py provides shortcuts (all, quick, framesize, combined, debug, single tick periods).

See TEST_INTEGRATION_README.md for the full command reference, per-test descriptions, and troubleshooting guide.

Files

File	Purpose
test_sent_integration.py	Main pytest suite (18 cases)
test_requirements.txt	Python dependencies
TEST_INTEGRATION_README.md	Full test documentation
run_tests.py	Cross-platform pytest runner with shortcuts
diagnostic.py	Standalone V/N/O/TX-mode probe for both ports

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Build

STM32CubeIDE manages the Makefile. To build from the command line, set the paths to the bundled tools and run make inside the Debug folder:

set MAKE=C:\ST\STM32CubeIDE_1.19.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.make.win32_2.2.0.202409170845\tools\bin\make.exe
set GCC=C:\ST\STM32CubeIDE_1.19.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.13.3.rel1.win32_1.0.0.202411081344\tools\bin
set PATH=%GCC%;%PATH%
cd Debug
%MAKE% -j4 all

Output: Debug/SENTToUSB.elf (~28 KB flash, ~6 KB RAM on STM32F042G4 with 32 KB flash / 6 KB SRAM).

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Flash

SWD (ST-Link)

set CLI=C:\ST\STM32CubeIDE_1.19.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.cubeprogrammer.win32_2.2.200.202503041107\tools\bin\STM32_Programmer_CLI.exe
%CLI% -c port=SWD freq=4000 -w Debug/SENTToUSB.elf -v -hardRst

USB DFU (no ST-Link required)

Step 1 — trigger DFU from the running device (replace COM8 with your port):

python -c "import serial,time; s=serial.Serial('COM8',115200,timeout=1); s.write(b'boot\r'); time.sleep(0.3); s.close()"

Step 2 — flash (~3 s after step 1, once the device enumerates as DFU):

%CLI% -c port=USB1 -w Debug/SENTToUSB.elf -v -hardRst

The boot command writes a magic value (0xDEADBEEF) to a .noinit RAM variable and resets. On the next boot the firmware detects the magic, clears it, and jumps to the STM32F042 ROM bootloader at 0x1FFFC400.

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FAQ

What is SENT (SAE J2716)? SENT (Single Edge Nibble Transmission) is the SAE J2716 / ISO 21097 single-wire digital protocol used by many modern automotive sensors — pressure, position, throttle, MAP, angle — to transmit data to an ECU. Each frame is a stream of 4-bit nibbles separated by falling edges, with a status nibble, data nibbles and a CRC.

What is the cheapest USB SENT analyzer? The uCanDevices SENT USB Converter is an open source SAE J2716 / ISO 21097 dongle around $23. It enumerates as a USB CDC virtual COM port on Windows 10+, Linux and macOS with no proprietary driver, and decodes 4-, 6- and 8-nibble SENT sensors with both DATA_ONLY and STATUS_AND_DATA CRC modes.

Can it auto-detect SENT tick period and CRC mode from an unknown sensor? Yes. Send t600104\r to enter Learn mode. The firmware auto-detects tick period (in 0.1 µs units), nibble count (4, 6 or 8) and CRC mode, then replies once with a 0x601 result frame. Send O\r afterwards to resume RX with the learned configuration.

Can it transmit SENT frames to simulate a sensor? Yes. Start TX mode with t600102\r, then send frame data as 0x520 CAN frames (B0 = status nibble, B1–B4 = data nibbles packed big-endian). Optional 0x600 / 05 control frame sets the TX tick period at runtime (2.0–90.0 µs). TX is driven from PB0 via TIM3 CH3 + DMA, so there is no per-interval ISR jitter.

Which sensors are known to work? The defaults are tuned for the MLX90377 angle sensor (3 µs tick, 6 nibbles, DATA_ONLY, seed 0x03). Other verified presets include the VW/Audi 04L 906 051 L DPF sensor (~3 µs, 6 nibbles, STATUS_AND_DATA, seed 0x05) and the GM 12643955 MAP sensor (~3 µs, 6 nibbles, DATA_ONLY, seed 0x05). For other sensors, use Learn mode.

What if my sensor uses a non-standard CRC seed? Both standard seeds are supported: 0x03 (SAE APR2016) and 0x05 (legacy / GM). Set the seed in B2 of the 0x001 configuration frame.

Is the firmware open source? Yes — STM32F042G4 firmware in this repository, SENT protocol layer in open-sent-c. A USB DFU bootloader is included; sent_viewer.py is a free GUI client.

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Related projects

• SENT protocol layer: open-sent-c
• Sibling products: USB LIN Converter, USB CAN Converter (UCCB), CAN FD USB Converter (CFUC)
• Product page: https://ucandevices.github.io/sentusb.html
• All uCanDevices products: https://ucandevices.github.io/
• Contact: devices.ucan@gmail.com