Hardware¶
What to connect between your MCU and an SFM4300, with which bus settings and timing, and the limits to stay inside.
All values here come from the SFM4300 datasheet (version 1.0, April 2022). Other SF06 parts (SFM3003, SFM3013, SFM3019, SFM3119) use the same command set with their own addresses, connectors and ratings: check their datasheets.
Connector and pins¶
A JST NSH connector, 6 circuits, 1.0 mm pitch (board part BM06B-NSHSS-TBT).
| Pin | Name | Notes |
|---|---|---|
| 1 | ADDR | Input: address select, open or GND, or a resistor to GND. Never connect it to VDD |
| 2 | SDA | I2C data; needs a pull-up |
| 3 | GND | Ground |
| 4 | VDD | Supply, 3.0 V to 5.5 V |
| 5 | SCL | I2C clock; needs a pull-up |
| 6 | IRQn | Output, active low: a sample is ready (or the sensor was reset). Leave it unconnected if unused |
I2C address¶
The ADDR pin selects one of four 7-bit addresses. Resistor tolerance must be ±5 % or better.
| ADDR | Address | sfm::addr:: |
|---|---|---|
| GND or open | 0x2A |
kSfm4300Default |
| 1.2 kΩ to GND | 0x2B |
kSfm4300Alt1 |
| 2.7 kΩ to GND | 0x2C |
kSfm4300Alt2 |
| 5.6 kΩ to GND | 0x2D |
kSfm4300Alt3 |
Default addresses of the other parts the driver knows: SFM3003-300-CL 0x28, SFM3003-300-CE 0x2D, SFM3119
0x29, SFM3019 0x2E, SFM3013 0x2F, SFM6000D 0x24 (sfm::addr). The soft reset uses the general-call
address 0x00.
Bus settings¶
| Setting | Value |
|---|---|
| Clock (fI2C) | 400 kHz typical, 1000 kHz maximum |
| Addressing | 7-bit, no register byte: a transfer is a raw write or a raw read |
| Command | 16 bits, MSB first; an argument adds 16 bits and a CRC-8 byte |
| Read | 16-bit words, MSB first, each followed by a CRC-8 byte; the host may stop after any word |
| CRC-8 | Polynomial 0x31, initial value 0xFF, no reflection, no final XOR; CRC(0xBEEF) = 0x92 |
| Pull-ups | Required on SDA and SCL, to the bus voltage; SDA and SCL must stay within -0.3 V to VDD + 0.3 V |
| No data | The sensor NACKs a read header while it has no new sample |
sequenceDiagram
participant H as Host (driver)
participant S as SFM4300
H->>S: write 0x3661 + arg 0x3608 + CRC (scaling for air)
H->>S: read 9 bytes
S-->>H: scale, offset, unit (each + CRC)
H->>S: write 0x3608 (start, air)
Note over S: first result after 12 ms
H->>S: read 9 bytes
S-->>H: flow, temperature, status (each + CRC)
H->>S: read 9 bytes (too early)
S--xH: NACK: no new sample (NoData)I2C protocol lists every command and frame.
Timing¶
| Parameter | Time | What the driver does |
|---|---|---|
| Power-up until the sensor answers | 16 ms typ., 20 ms max. | Nothing: power the sensor before the first call |
| Soft reset or exit sleep until ready | 16 ms typ., 20 ms max. | SoftReset() waits 20 ms; ExitSleep() polls for up to 20 ms |
| First result after a start command | 12 ms | StartContinuous() waits 12 ms |
| Warm-up for an accurate result | 30 ms typ. (includes the 12 ms) | Nothing: discard readings in the first 30 ms |
| Stop until the next command | 0.5 ms max. | Stop() waits 1 ms |
| Settling after a change of gas | 70 ms typ. | |
| Flow update rate, no averaging | 2000 Hz (1800 to 2200) | |
| Temperature update rate | 90 Hz (80 to 100) |
Power¶
| Parameter | Value | Notes |
|---|---|---|
| Supply voltage VDD | 3.0 V to 5.5 V, 3.3 V typ. | Calibrated at 3.3 V; 3.3 V ±5 % is recommended |
| Power-up / power-down threshold | 2.3 V to 2.7 V, 2.5 V typ. | |
| Supply current, measuring | 4.2 mA typ., 5.7 mA max. | At VDD = 3.3 V |
| Supply current, idle | 0.055 mA typ., 0.6 mA max. | |
| Supply current, sleep | 0.4 µA typ., 1 µA max. |
Absolute maximum VDD is 5.5 V. The operating temperature range is +5 °C to +50 °C; storage -40 °C to +80 °C.
Fluidics¶
| Parameter | Value |
|---|---|
| Operating pressure | 0.66 bar to 7 bar absolute |
| Allowable overpressure | 10 bar gauge (no damage; specifications apply again afterwards) |
| Burst pressure | 20 bar gauge minimum |
| Pressure drop | Under 25 mbar at 20 slm (both ranges); under 100 mbar at 50 slm (SFM4300-50) |
| Orientation | Calibrated horizontal, connector facing up; other orientations add a small offset |
| Fitting suffix | Connection |
|---|---|
-B |
Basemount flanges, base plate with 7 mm inner-diameter openings. Fix it with the side screw holes only |
-O |
O-ring connection, port matched to an O-ring fitting with 8 mm inner-diameter openings |
-P |
8 mm Legris push-in fittings: tube outer diameter 8 mm, inner diameter 6 mm or more |
The temperature the sensor reports is that of its silicon, not of the gas. It follows the gas, but also the sensor's surroundings.
Evaluation kit¶
| Kit | Contents |
|---|---|
| SEK-SFM4300-20-P | An SFM4300-20-P and an adapter cable; the SEK sensor bridge is ordered separately |
The ESP32 examples run on an ESP32-S3 with SDA on GPIO 8 and SCL on GPIO 9 at 400 kHz; the
pins are set in each example's using I2c = SfmEspIdfI2c<...> line.
Reference documents¶
| Document | What it is for |
|---|---|
| SFM4300 datasheet | Pins, electrical and fluidic limits, timing, the SF06 command set, scaling |
Sensirion/embedded-i2c-sfm-sf06 |
Sensirion's reference C driver (BSD-3-Clause); the protocol constants were cross-checked against it |
THIRD_PARTY_NOTICES.md |
Its licence notice |
| NXP UM10204 | I2C-bus specification (rise times, pull-up sizing) |