Hardware¶
What to connect between your MCU and an FDO2-G2, with which UART settings, and the timing and power the module needs.
All values here come from the FDO2-G2 datasheet (document version v5, 03/2026): specifications in section 2, the interface in section 4, the connector in section 7.
Connector¶
The module has a Molex 560020-0420 socket (four positions) on its back, next to the venting capillary. Directions are seen from the sensor.
| Pin | Name | Function |
|---|---|---|
| 1 | GND | Ground |
| 2 | TXD | Output: UART transmit, 3.0 V levels |
| 3 | RXD | Input: UART receive, 3.0 V levels, 3.3 V tolerant |
| 4 | VCC | Supply, 3.3 V to 5.0 V DC |
Connect MCU TX to pin 3 and MCU RX to pin 2. There are no other control pins: no reset, enable or interrupt line. The module is always on while VCC is present.
3.3 V maximum on RXD
The UART runs at 3.0 V and its absolute maximum is 3.3 V. A 3.3 V MCU can drive RXD directly; a 5 V MCU needs a level shifter or a divider on its TX line. The 3.0 V high level on TXD is above the input-high threshold of most 3.3 V MCUs; check yours.
UART settings¶
| Setting | Value |
|---|---|
| Baud rate | 19200 after every power-up (fdo2::kFdo2G2DefaultBaud) |
| Frame | 8 data bits, no parity, 1 stop bit |
| Flow control | None |
| Command end | CR (0x0D), or CR LF |
| Reply end | CR only |
| Other rates | 1200 to 115200 with #BAUD, until the next power cycle; the driver does not send it |
The datasheet recommends 19200 for the highest reliability. At 19200 baud a #MOXY reply (about 25 characters)
takes about 13 ms on the wire.
Timing¶
| Event | Time |
|---|---|
| Power-up to first command | about 1 s (kFdo2G2PowerUpSettleMs = 1100 ms) |
| Measurement, M = 0 to 2 (factory: 2) | up to about 150 ms |
| Measurement, M = 3 or 4 | up to about 300 ms |
#CALO or #CAHI calibration |
up to 10 s |
| Response time t63 | under 2 s |
| Warm-up to full accuracy | 3 min |
M is the flash duration mode set with #SETM (section 4.3); response time and warm-up are from section 2.
The module measures only when asked (unless broadcast mode is on), so the measurement time is part of every
#MOXY and #MRAW transaction:
sequenceDiagram
participant H as Host (driver)
participant S as FDO2-G2
H->>H: flush_rx()
H->>S: MOXY command, CR
Note over S: temperature, ambient light, oxygen, housing sensors (up to 150 ms at M = 2)
S-->>H: MOXY 203456 17892 0, CR
H->>H: parse, scale: 203.456 hPa, 17.892 C, status 0The driver's default measurement timeout is 250 ms. Raise it with SetMeasureTimeoutMs() if the module is set to
M = 3 or 4 (Configuration).
Power¶
| Parameter | Value |
|---|---|
| Supply voltage | 3.3 V to 5.0 V DC |
| Absolute maximum supply | 5.5 V DC |
| Current, standby / peak | about 8 mA / 40 mA |
| Energy per measurement | about 1 to 2 mAs |
Do not interrupt the supply while the module writes its flash (after #CALO, #CAHI, #CRCE, #SETM or
#BCST): the datasheet warns that the flash can be corrupted. The driver sends none of these commands.
Environment and mounting¶
| Parameter | Value |
|---|---|
| Operating temperature | −10 °C to 60 °C |
| Storage temperature | −40 °C to 60 °C |
| Internal pressure sensor range | 300 mbar to 1100 mbar |
| Maximum absolute / differential pressure | 20 bar / 3 bar |
| Humidity | back side non-condensing; no dew point inside the membrane |
| Mounting | M16 x 1 thread; Ø 28.5 mm x 28 mm; 10.5 g |
Keep direct sunlight and strong lamps off the sensing membrane: ambient light shows up in the status word and in
the #MRAW ambient-light field. The cross-sensitivity table (section 3) lists the gases that disturb or damage the
sensor, NO2 and Cl2 among them.
Errata¶
| Erratum | Affects | Status |
|---|---|---|
| Increased noise at two module-specific temperatures, typically between 8 °C and 15 °C, each about ±0.1 °C wide | Firmware 3.55 | Fixed in firmware 3.57 with a hardware change (PCN-FDO2-G2-001) |
ReadVersion() returns the firmware revision: firmware_revision 357 is 3.57.
Evaluation¶
PyroScience sells the module with a USB adapter cable and the "Simple FDO2 Logger" software for Windows, which installs a virtual COM port to the module's UART. It is a quick way to see the module answer before you wire it to an MCU. The ESP32 examples run on an ESP32-S3 with the module on UART1.
Reference documents¶
| Document | What it is for |
|---|---|
| FDO2-G2 datasheet | Specifications, the UART command set, error codes, connector, errata |
| PyroScience FDO2-G2 product page | Accessories, newer datasheet revisions |