QTFM Gen-2 Quick Reference

Looking for step-by-step sync setup (wired, External PPS, or wireless GPS via Magpie)? See the Syncing Your Gen-2 QTFM Sensors guide.

LED Color Codes

LED visible on the sensor ECU.

State	Description
Flashing Red	Idle (flashes every 1 s in Master mode and every 0.5 s in Slave mode)
Solid Yellow	Autostart in progress
Solid Blue	Transmitting valid magnetic field data
Solid Red	Bad data (high gradient or in a dead zone)
Solid White New in V1_43 Magpie only	GPS wireless-sync indicator (default). When GPS Sync mode is active, the sensor is receiving valid UTC frames (forwarded by a Magpie), and the current measurement is good, the LED is steady white. It is held at constant brightness, so it adds no per-second magnetic signature. (Bad data shows solid red instead.) For a per-second multi-sensor visual sync check, switch to the rainbow with sensor command `235`. See the Syncing guide.
Per-Second Rainbow cmd 235 (optional) Magpie only	Troubleshooting sync view for GPS wireless sync (off by default). When enabled with sensor command `235`, the LED steps through a 5-color sequence (Yellow → Green → Cyan → Blue → Purple), one color per UTC second, in lockstep across all synced sensors — properly synchronized sensors show the same color at the same instant. Not the default because stepping the LED current each second radiates a small 1 Hz magnetic signature; reverts to solid white on reboot. Red still overrides on bad data.

Sensor Configuration Options

Retained in internal flash memory. Configurable via the user interface software or with serial commands.

Data Rate	1 / 2 / 4 / 8 / 16 / 32 / 64 / 128 / 1000 / 2000 ms
Print Items	Sensitivity / Data drop counter / Timestamp
Filters	50 or 60 Hz notch / 10 Hz low or highpass / 20 Hz low or highpass / Custom low or highpass / Off
Magnetic Environment Scalar	Noisy / Average / Quiet / Auto-optimize / Custom (SZC)
Magnetic Environment Vector	Noisy / Average / Quiet / Auto-optimize / Custom (VZC)
Vector Mode	Enabled / Disabled (requires add-on vector coils)
Vector Mode Type	Survey (default, two averaged measurements per output, requires vector-coil calibration) / Stable (single measurement, no calibration required). See Vector mode: Survey vs Stable.
Automatic Start-Up	Enabled / Disabled
Baudrate	115200 / 230400 / 19200 bits
Sync Mode	Master / Slave / External PPS Sync / GPS Sync V1_43

More info on sensor configuration: Sensor Configuration.

Serial Commands

Every QTFM Gen-2 user command lives in this one table — each appears exactly once. Commands are sent over the configured baudrate as a single ASCII character (the ASCII column) or, for the higher-numbered sync/operation commands, as their decimal value; some accept a numeric argument terminated by \r\n. The separator rows group related commands (sync, filters, print/display, measurement, vector, baud); a dash in the ASCII column marks decimal-only commands that have no printable single-character form. Step-by-step sync setup lives in the Syncing Your Gen-2 QTFM Sensors guide; this page is the command dictionary.

Decimal	ASCII	Command	Description
System & Startup
76	L	Autostart	Initiate Autostart process
79	O	Toggle self boot	Automatic autostart when sensor powers on. This command toggles the setting on or off
101	e	Reboot	Software sensor reboot
115	s	Startup settings	Print all startup settings
34	"	Print Sensor Info Short	Print sensor serial number and other permanent settings. The `#MS Mode:` line reports the active sync mode (the cached value of FPGA address 30), so this is also how you confirm Master / Slave / External PPS Sync / GPS Sync.
Utility & Custom Profile Tilde Commands tilde-prefixed commands for sensor state control, scripted configuration, and user-saveable profile slots. All tilde commands bypass the ASCII command lock, so they keep working after `~Lock_Commands~` is enabled. Decimal column is dashed because these commands have no equivalent single-character form.
—	~	~Start~	Enable autostart on power-up (writes EEPROM 269 = 1) and reboot. The sensor will begin measurements immediately after every power cycle from now on.
—	~	~Stop~ New V1_44	Universal abort. Drops the sensor into idle without rebooting: aborts any active autostart, cancels queued LI_Set / Reop_Heading / Warmup, disables autostart-on-power (EEPROM 269 = 0), turns off cell heater + laser heater + laser, restores Laser_SP / Laser_Max from EEPROM (so any RAM bumps clear cleanly), and resets internal state. The single command to use when something is going wrong or you want a known-clean idle.
—	~	~apply~ New V1_44	Re-read EEPROM into the sensor’s live runtime variables without rebooting. Pairs with `~ADDR,VAL~` (and the legacy `=ADDR\r\nVAL\r\n`) writes so a batch of changes takes effect in one shot. Covers the 26 settings in the Configuration Settings Overview plus filter coefficients (recomputes `Filter_startup()`) and the derived float at address 354. Baud rate (291) still requires a reboot.
—	~	~Warmup~ — or — ~WU~ New V1_44	Background thermal pre-warmup. Turns the laser ON at present `Laser_SP`, drives the cell heater at 50% of `CH_Auto_time`, and the laser heater at approximately 28% above `LH_mintime`. Monitors PD; when PD reaches 90% of `Light_Level_Set` the laser heater turns off and the cell heater holds. Useful for cold-start workflows where you want the sensor at operating temperature before the host triggers autostart. Cancel with `~Stop~`.
—	~	~report~ New V1_44	Print every configuration setting as a three-column table: address, current EEPROM value, and a friendly label. Closes with the supported single-address and coupled shortcuts so the operator has the syntax in front of them. Use it to confirm sensor state before `~apply~` or autostart.
—	~	~ADDR,VAL~ New V1_44	Direct EEPROM write shorthand. Writes integer VAL to address ADDR (0–400). Example: `~30,1~` sets Master mode. Floats are not supported — use the older `=ADDR\r\nVAL\r\n` form for the few float-valued addresses (laser PID gains, etc.). Bypasses the ASCII command lock.
—	~	~ADDR,VAL,PARAM~ New V1_44	Coupled-write shortcut for settings split across multiple addresses. Supported dispatches: `~285,8,fc~` (Custom Lowpass filter at fc Hz), `~315,V,N~` (VZC mode — V=0 auto / V=1 fixed, N=count), `~353,V,S~` (Fixed Measurement Time — V=0/1, S=1/2/3 → 100/200/300µs). Other addresses with three arguments are rejected with a helpful message.
—	~	~Lock_Commands~	Enable the ASCII command lock. After this, single-character decimal commands print `#Commands_Locked` and are ignored. Tilde commands still work. Useful for integrators who want to harden the sensor against stray serial keystrokes.
—	~	~Unlock_Commands~	Disable the ASCII command lock and restore normal command handling.
—	~	~SaveSlotN_name~ New V1_44	Snapshot the sensor’s current live configuration into custom profile slot N (1, 2, or 3) under name (up to 16 ASCII characters; letters, digits, underscores). Replaces any previous contents of that slot. Does not reboot. Example: `~SaveSlot1_GroundSurvey_250~`.
—	~	~LoadSlotN~ New V1_44	Apply the configuration saved in custom slot N, then reboot. You can also use the bare-name form — `~name~` — just like a built-in profile name; built-in names take precedence if there is a collision.
—	~	~ListSlots~ New V1_44	Print the contents of all three custom profile slots. Valid slots show their saved name; unused slots show `(empty)`. Does not reboot.
—	~	~DelSlotN~ New V1_44	Clear custom slot N. The slot becomes available for a new save. Does not reboot.
—	~	~profile_name~	Bare-name profile load. Looks up the name against built-in profiles first (see the Profile Configuration guide for the full catalog), then falls back to your saved custom slots. Applies the matching profile and reboots.
Filters
117	u	60 Hz Notch Filter	Turn on 60 Hz notch filter
118	v	50 Hz Notch Filter	Turn on 50 Hz notch filter
119	w	Highpass 10 Hz Filter	Turn on 10 Hz highpass filter
120	x	Highpass 20 Hz Filter	Turn on 20 Hz highpass filter
121	y	Lowpass 10 Hz Filter	Turn on 10 Hz lowpass filter
122	z	Lowpass 20 Hz Filter	Turn on 20 Hz lowpass filter
123	{	Filters Off	Turn off all filters
Print & Display Toggles on/off print items, including the onboard IMU channels (ECU V8+)
43	+	Print Sensitivity	Toggle on and off with the command
108	l	Print Data drop counter	Toggle on and off with the command
109	m	Print Timestamp	Toggle the millisecond timestamp print on and off. Leave this on unless you have a reason not to — it is the QTFM’s standard timestamp, from the sensor’s own jitter-free clock, and the correct time base for analysis. A Magpie or ACB adds its own microsecond timestamp, but that is for GPS correlation and drop monitoring, not measurement timing.
42	*	White LED Mode	Toggle on and off. Forces the ECU LED to be white. Useful for determining which sensor is connected to the COM port when multiple sensors are connected.
82	R	Toggle IMU Accel Print	Onboard ICM-20948 IMU accelerometer. Echoes `#Print IMU Acc On` / `Off`. Retained in flash (EEPROM address 286).
83	S	Toggle IMU Gyro Print	Echoes `#Print IMU Gyro On` / `Off`. Retained in flash (EEPROM address 287).
85	U	Toggle IMU Mag Print	Toggles the IMU’s secondary 3-axis magnetometer (AK09916) output. Echoes `#Print IMU V.Mag On` / `Off`. Retained in flash (EEPROM address 288).
86	V	Toggle IMU Temp Print	Echoes `#Print IMU Temp On` / `Off`. Retained in flash (EEPROM address 289).
Measurement, Environment & Zero-Crossing
125	}	Change Data Rate	Cycle through Data Rate settings
106	j	Environment Setting Vector	Cycle through environment settings for vector mode (change VZC)
107	k	Environment Setting Scalar	Cycle through environment settings for scalar mode (change SZC)
105	i	Set Custom ZC	Mem Add 2 (custom SZC): Mem Add 305 (custom VZC). Mem Write Int button to set address.
59	;	Auto optimize ZC	Automatically optimizes measured zero crossings
60	<	Announce ZC	Readback of measurement zero crossings in scalar and vector mode
Vector Mode
90	Z	Toggle Vector Mode	Vector mode on/off (enable/disable the vector output entirely). Requires add-on vector coils.
227	ã	Toggle Vector Mode Type	Toggle vector mode between Survey (default, two averaged measurements per output) and Stable (single measurement, no coil calibration required). See Vector mode: Survey vs Stable.
Baud Rate
40	(	Change Baud Rate	Needs to be followed by the desired rate. Ex. `(115200*`
41	)	Baud Rate Statement	Announce current baud rate
User Reoptimization & Calibration command-line procedures for re-tuning the sensor after long deployment, temperature drift, or hardware change. Step-by-step workflow lives in the Reoptimization guide (basic + laser-gain) and the Vector coil calibration guide (vector add-on only).
7	—	Print Optimization Parameters	Print all current optimization parameters (PID gains, lock setpoints, WL offsets, deltas) along with the sensor serial number and firmware version. Run before and after a reoptimization to confirm what changed.
3	—	Auto Reoptimization — Part 1	Start the first basic-reoptimization phase (approximately 30 s, two automatic reboots). Refines the core operating parameters that drift over long deployments.
4	—	Auto Reoptimization — Part 2	Second basic-reoptimization phase (approximately 30 s). Requires laser-lock + cell-lock + autostart-complete. Determines the WL offset and refines the lock setpoints.
5	—	Save Basic Reoptimization	Finalize the basic reoptimization by writing the new values to flash. Only takes effect when the post-reopt WL offset and `WL_R_Max` meet validity checks; otherwise prints a refusal so the operator re-runs the steps.
224	—	Recalculate Laser-Lock Gains (Standard)	Auto-recalculate the laser-lock PID gains into reoptimization staging slots (EEPROM addresses 326, 327, 342). Uses the standard starting P = 28. Requires laser-lock + cell-lock active. Sensor prints several unstable messages while it converges — expected.
225	—	Recalculate Laser-Lock Gains (Low Laser Power)	Same procedure as cmd 224 but starts from a lower P = 12. Use this variant when the laser power has been reduced from default — the higher-P gains from cmd 224 can fail to converge in reasonable time at lower laser power, while the lower-P gains here settle quickly.
223	—	Apply New Laser-Lock Gains	Promote the recalculated gains from staging (326, 327, 342) to the active locked-mode gain registers (271, 300, 335). Run after 224 or 225 and after verifying the sensor still locks through normal orientation changes.
6	—	Initiate Vector Coil Calibration	Start the vector-coil delta calibration (1–2 min). Sensor prints `#Calibrating Coil, keep sensor still` and measures Delta_X / Delta_Y / Delta_Z. Requires the vector add-on, Vector Mode enabled, laser-lock + cell-lock.
9	—	Save Vector Coil Calibration	Permanently store the measured Delta_X / Delta_Y / Delta_Z values to EEPROM (338, 339, 340). Only writes if all three deltas are > 500 (validity guard); otherwise refuses.
203	Ë	Factory Reset	Reset EEPROM to factory defaults. Two equivalent ways to send it: the decimal-203 form must be followed by the confirmation code `2023` (e.g. `Ë2023` or `2032023`); or send the tilde form `~Reset_EEPROM~` which performs the same reset without a separate confirmation code. Requires a full reoptimization afterward.
Sync — Modes, Operations & Trigger all sync commands grouped together: mode selection (32/33/112/113), the wired trigger (84), and the PPS/GPS operations (206–235)
32	space	Master Mode	Sync mode. Sensor runs on its own internal clock and pulses out a 1 Hz sync signal that downstream slaves can lock to. FPGA addr 30 = 1.
33	!	Slave Mode	Sync mode. Sensor slaves to the external clock input on the sync line (typically driven by a Master sensor); prints `#needs input clock` if the input clock is missing. FPGA addr 30 = 0.
112	p	External PPS Sync Mode New FPGA v5.05+	Sync mode. Slaves the 1 Hz cycle counter to an externally supplied PPS edge (e.g. a 1 PPS GPS pulse routed through a host ECU). No UTC time is exchanged — the shared edge keeps every sensor’s cycle boundaries aligned in lockstep. FPGA addr 30 = 2. See sync operations 231–234 below.
113	q	GPS Sync Mode New FPGA v5.05+ Magpie only	Sync mode. Same as External PPS Sync, plus the sensor accepts an 11-byte UTC time frame over UART (Serial4 on the QTFM). A Magpie with an attached GPS receiver sends the frame and the sensor realigns its internal sample counter to absolute UTC milliseconds. FPGA addr 30 = 3. Setup & frame format: Syncing guide — Wireless GPS.
84	T	Sync (wired)	Trigger a sync of all wired Master/Slave sensors chained together.
206	—	Toggle GPS Sync New	Enable / disable the sensor’s response to incoming UTC frames. When enabled, both `GPS_Sync` and `GPS_Active_Sync` flags are set; the sensor will act on the next valid UTC frame. When disabled, frames are received and logged but the sensor does not realign. `#GPS Sync: ENABLED # GPS_Sync=1, GPS_Active_Sync=1 # Sensor will realign cycle counter on next valid UTC frame + PPS edge. # Send cmd 209 to arm a one-shot edge alignment. # UTC frames received so far: good=N bad=N` When disabled, the output reads `#GPS Sync: DISABLED` and notes that incoming frames will be received but ignored.
207	—	Toggle GPS Edge Sync New	Toggle the `GPS_Edge_Sync` flag directly. Normally set as a side-effect of command 209 + a valid UTC frame; manual toggling is for advanced bring-up.
209	—	Arm Edge Sync (one-shot) New	Sets `PPS_Edge_Sync_Arm = true`. The next valid UTC frame will trigger a single one-shot alignment of the sensor’s cycle counter to the PPS edge. The arm flag clears automatically after the alignment fires; re-arm by sending the command again. `#PPS Edge Sync: ARMED # PPS_Edge_Sync_Arm=1 (one-shot - clears automatically after firing) # Next valid UTC frame will trigger a one-shot cycle realignment. # UTC frames received so far: good=N bad=N` If `GPS_Sync` is off when this command is sent, the output reminds the operator to send cmd 206 first.
230	—	Toggle Periodic Edge Re-Arm New	Toggles a background process that automatically re-arms `PPS_Edge_Sync_Arm` at a fixed interval (default 60 s). Used for long-running deployments where the sensor’s local clock would otherwise drift out of phase with the GPS-derived UTC time over hours. Persisted to EEPROM (address 356), so it survives reboots and re-engages automatically after the cell locks. PPS-loss safety. If UTC frames stop arriving (PPS lost, GPS antenna disconnected, Magpie powered off, etc.) the periodic re-arm is automatically suppressed within approximately 3 seconds, and resumes automatically when UTC frames return. `#Periodic Edge Sync Re-Arm: ENABLED # Will re-arm PPS_Edge_Sync_Arm every 60 seconds. # Suppressed if no UTC frame received in last 3000 ms (PPS lost). # UTC frames received so far: good=N bad=N` The re-arm events themselves are silent (no per-fire serial print). Visual confirmation is the steady solid white sync LED (or, with the rainbow enabled via cmd 235, the per-second color stepping in lockstep across all synced sensors).
231	—	Realign on Next PPS (one-shot) New	Arms a one-shot realignment that fires on the next valid PPS edge. “Realign” here means: reset the sensor’s millisecond timestamp, restart the averaging window, and re-coincide the vector Bx/By/Bz sample phases — the same operation the wired `Sensor_Sync()` performs. For External PPS Sync arrays: because every sensor wired to the same PPS sees the same edge, broadcasting this command to all sensors within a single PPS second makes them all realign on the same edge. One-shot — it disarms itself after firing. `#PPS realign ARMED: realign on the NEXT valid PPS edge (one-shot). # Broadcast this to all sensors within one PPS second so they fire on the same edge.` On firing: `#PPS realign DONE (ms timestamp + averaging + X/Y/Z phase reset on PPS edge).`
232	—	Realign After PPS Dropout (one-shot) New	Arms a one-shot realignment driven entirely by the PPS signal — no per-sensor command at fire time. After arming, the sensor first confirms the PPS is alive, then waits for the operator to briefly disconnect the shared PPS; when it resumes, the sensor realigns on the 3rd valid edge after resume (letting the input re-stabilize), then disarms. Cutting and restoring one shared PPS line therefore realigns an entire array together. One-shot — never auto re-arms. `#PPS realign ARMED (dropout mode): cut the shared PPS, then realign on valid edge #3 after it resumes (one-shot, never auto re-arms).`
233	—	Disarm PPS Realign New	Cancels any pending realignment armed by cmd 231 or 232. Output: `#PPS realign DISARMED.`
234	—	Toggle External-PPS Status Debug New	Toggles an approximately 1 Hz debug line used to confirm the sensor is actually receiving and locking to the external PPS — run it during External PPS bring-up before relying on the signal. `#PPS dbg: alive=1 edges=1234 dt=1000ms offset=27 locked=1 mode=0 resume_n=0` `alive` — 1 if a valid PPS edge was seen within the last 2.5 s. `edges` — running count of valid PPS edges (FPGA PPS counter). Stepping by 1 each second means the PPS is being received. `dt` — milliseconds since the last valid edge. `offset` — measured cycle-vs-PPS-edge offset, in FPGA ticks. `locked` — 1 when `offset` is inside the edge-sync window [15,35] ticks (cycle is edge-locked to the PPS). `mode` / `resume_n` — current realign arming state (0=off, 1=next-edge, 2/3/4=dropout sub-states) and the resume-edge count.
235	—	Toggle GPS-Sync LED Style New Magpie only	Switches the sync indicator between solid white (default) and a per-second rainbow, for GPS wireless sync only. Solid white (default) — steady white whenever the sensor is GPS-wireless synced and the current measurement is good. Held at constant brightness, so it adds no once-per-second LED drive-current change near the sensor. Rainbow (toggle on) — the LED steps through a 5-color sequence, one color per UTC second, in lockstep across all synced sensors. Handy as an at-a-glance confirmation that sync is live, but the per-second change radiates a small 1 Hz magnetic signature, so it is for troubleshooting rather than recording clean data. Red overrides either style whenever the latest measurement is flagged bad. Not saved — the LED returns to solid white on every reboot. Output: `#GPS sync LED: WHITE (synced + data good)` or `#GPS sync LED: RAINBOW (troubleshooting)`. Has no effect outside GPS wireless sync mode.

IMU not detected If a sensor responds to commands 82 / 83 / 85 / 86 with #No IMU Detected, ECU Must Be V8 Or Later, the ECU hardware does not have the onboard ICM-20948 IMU populated; the print flag is left unchanged.

FPGA hardware requirement Sync modes 112 (External PPS) and 113 (GPS) require the FPGA bitstream to be at v5.05 or later. On a v5.04 or older bitstream, sending command p or q is rejected with an informative message and the existing sync mode is left unchanged. Confirm the active mode anytime with " (decimal 34) — the #MS Mode: line reports the cached value of FPGA address 30. The FPGA bitstream cannot be updated remotely — sensors purchased June 2026 or later ship with v5.05+; earlier units must be returned to QuSpin for the upgrade. The wired Master/Slave method (modes 32/33) works on every Gen-2 sensor regardless of FPGA version.

Vector Mode: Survey vs Stable

When Vector Mode is enabled (command Z, decimal 90), the QTFM Gen-2 can run its vector output in one of two distinct measurement schemes. The active scheme is toggled with command 227 and retained in flash memory across reboots.

Mode	Description
Survey Default	Each vector output is the average of two vector measurements taken in opposite coil-bias states. This averaging cancels much of the high-frequency noise that would otherwise show up at the vector output, so Survey mode is the right choice when the magnetic environment is dynamic or RF-noisy. The trade-off is that the two-measurement scheme is sensitive to low-frequency drift in the vector coil response, so Survey mode requires a vector-coil calibration to keep the output accurate. See Vector coil calibration for the calibration procedure.
Stable	Each vector output is a single vector measurement. Because there is no opposite-bias averaging, Stable mode is less tolerant of high-frequency noise — the noise floor at the vector output will be higher in an RF-noisy environment. In exchange, Stable mode has extremely good long-term stability and does not require vector coil calibration, which makes it the better choice for static deployments and long-duration measurements where drift matters more than instantaneous noise.

Mode

Description

Survey Default

Each vector output is the average of two vector measurements taken in opposite coil-bias states. This averaging cancels much of the high-frequency noise that would otherwise show up at the vector output, so Survey mode is the right choice when the magnetic environment is dynamic or RF-noisy. The trade-off is that the two-measurement scheme is sensitive to low-frequency drift in the vector coil response, so Survey mode requires a vector-coil calibration to keep the output accurate. See Vector coil calibration for the calibration procedure.

Stable

Each vector output is a single vector measurement. Because there is no opposite-bias averaging, Stable mode is less tolerant of high-frequency noise — the noise floor at the vector output will be higher in an RF-noisy environment. In exchange, Stable mode has extremely good long-term stability and does not require vector coil calibration, which makes it the better choice for static deployments and long-duration measurements where drift matters more than instantaneous noise.

Switching modes

Send decimal 227 to toggle between Survey (default) and Stable. The sensor replies with one of:

#Vector_Mode: 0, Survey(default)
#Vector_Mode: 1, Stable

The new mode is written to EEPROM address 341 and applied on every subsequent boot until changed again.

Which should I use? If you operate in environments with significant RF or 60 Hz noise and can perform a vector-coil calibration every few weeks, Survey mode will give you a cleaner output. If you need set-it-and-forget-it long-term stability — especially for stationary installations — Stable mode is the better default.

Document version 2026-05-27 · matches firmware V1_43

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