A Z probe can be used to accurately, automatically and repeatably set the Z height, assist in the manual adjustment of the bed level, and/or allow automatic correction/compensation for errors of bed squareness and flatness. On a delta machine, it can automatically calibrate the machine dimensions.

Differing Z probe technologies vary in their ability to deliver reliability, simplicity, accuracy and low cost and no single type predominates. For a comparison of advantages and disadvantages for various Z probe options see Choosing a Z probe.

Once you have the probe connected, see how to:

• Test and calibrate a Z probe
• Setting up automatic probing of the print bed
• Using the Manual Bed Levelling Assistant
• Bed levelling using multiple independent Z motors
• Mesh bed compensation

If you don't have a Z probe, you can still use mesh bed compensation and other features normally associated with a Z probe. See Mode 0 below.

You can connect a Z probe directly to your Duet.

• On Duet 3 boards, you can connect a probe to any IO connector. Some probes may need specific capabilities e.g. analog input or PWM output; see the hardware overview for your board for IO connector capabilities.
• The Duet 2 WiFi / Ethernet and Duet 0.8.5 provide a dedicated 4-pin connector for connecting a Z probe.
• The Duet 2 Maestro provides a dedicated 5-pin connector.
• The Duet 0.6 does not have the Z-probe connector, but you can use some pins on the expansion connector for the same purpose.

Caution! The following table shows the pinout out by function, and NOT the physical order. Check the wiring diagram of your Duet for the correct pinout order. For example, the pinout of the 5-pin IO_ connectors on Duet 3 is NOT the same as the pinout of the 5-pin Z Probe connector on Duet Maestro!

Duet WiFi/Ethernet pin marking	Duet Maestro pin marking	Duet 3 pin marking	Duet 0.8.5 pin marking	Duet 0.6 expansion connector pin	Purpose
IN	IN	IN	AD12	39 (AD12)	Input from Z probe
GND	GND	GND	GND	2 (or use the GND pin on E0 endstop connector)	Ground
MOD	MOD	OUT	PC10	41 (AD14)	Control signal for some types of Z probe
3.3V	3.3V	3.3V	3.3V	3 (or use the 3V3 pin on E0 endstop connector)	Power to Z probe
-	5V	5V	-	-	5V power to Z probes that need it (e.g. BLTouch)

Note: The MOD pin on the Duet 2 WiFi/Ethernet is NOT PWM capable, so can't be used to control a servo. The IOx_out pin on Duet 3 and the MOD pin on the Duet 2 Maestro are PWM capable, and can control a servo (eg to deploy BLTouch).

The M558 Gcode configures the firmware for your Z probe. Using the P parameter configures the firmware to recognise the output mode of the Z probe you are using. For example, M558 P1 selects Z probe mode 1.

• You can use a Z probe with either an analog or a digital output; just set the mode in M558 accordingly.
• In firmware versions before 3.2, when using a probe with analog output, the firmware will slow down the probe speed when it is getting close to trigger height.
• In firmware versions from 3.2, you can use the M558 F parameter to specify a fast Z feedrate for the first probing move, followed by a slower second probing move, for any probe. eg M558 F600:120
• Some types of Z probe with digital output should be connected to the E0 endstop connector instead of the Z probe connector.

The following table gives an overview of the different Z probe modes.

Mode	Probe type	Control signal (MOD or OUT pin)	Notes
0	No probe	Not used
1	Analogue probe	HIGH
2	Analogue probe with modulation	Modulation (IR LED on/off control)
3	Analogue probe	LOW
4	Digital probe connected to E0 endstop input, or endstop input set by C parameter	Not used	Not supported in RRF 3. Use type 5 or 8. See M558 documentation
5	Digital probe connected to Z Probe input	HIGH during probing, LOW at other times
6	Digital probe connected to E1 endstop input	Not used	Not supported in RRF 3. Use type 5 or 8. See M558 documentation
7	Switch triggering Z endstop	Not used	Not supported in RRF 3. Use type 5 or 8. See M558 documentation
8	Digital probe connected to Z Probe input, unfiltered	HIGH during probing, LOW at other times
9	BLTouch with output connected to Z Probe input	OUT (Duet 3) and MOD (Duet 2 Maestro) can be configured to control deployment/retraction. MOD on Duet 2 WiFi/Ethernet is not PWM capable, so use heater pin on expansion port instead.
10	Z motor stall detection	Not used

Details:

Select this mode if you have no Z probe. When the firmware tries to execute a command to probe the bed, it will instead show a dialogue in Duet Web Control, and also on Panel Due if you are running recent Panel Due firmware, asking you to jog the head down until the nozzle just touches the bed and then press the OK button.

This is a probe with an analog output connected to the Z probe connector. The probe output must rise as it gets closer to the bed, unless you use parameter I1 in the M558 command to indicate that the probe output falls as it gets closer to the bed (the I1 parameter is supported in firmware 1.16 and later). The control signal is driven HIGH.

This is a probe with an analog output that requires the Duet to provide modulation signal and demodulate the returned signal. The probe output rises as it gets closer to the bed. The Duet drives the control signal with a 250Hz square wave. The firmware extracts that part of the analog signal received on the IN pin that is in phase with the modulation.

As mode 1 except that the control signal is driven LOW.

The trigger signal is read from the E0 endstop circuit. You can choose whether the signal is high or low when triggered. In firmware 1.15 and earlier this is done by using M574 E0 S1 to select active high, or M574 E0 S0 to select active low. In firmware 1.16 and later, use I1 in the M558 command to select active low, otherwise it defaults to active high. The device connected to the E0 STP pin must be able to sink 1.5mA for the Duet 2 WiFi and Duet 2 Ethernet, 0.3mA for the Duet 2 Maestro, or 2.1mA for the Duet 0.6 or 0.8.5. In firmware 2.03 and later you can choose a different endstop input using the C parameter of the M558 command.

A switch or digital output device connected between the IN and GND terminals of the Z probe connector. Similar to mode 4 except that the Z probe connector is used. The input must be active high when triggered, or in firmware 1.16 and later you can use the I1 parameter in the M558 command to select active low. The only pullup resistor is the 100K nominal pullup in the microcontroller so the sink current requirement is tiny.

Similar to mode 4 except that the E1 endstop input is used. Deprecated in firmware 2.03 and later, use mode 4 with parameter C4 instead.

Similar to mode 4 except that the Z endstop input is used. Deprecated in firmware 2.03 and later, use mode 4 with parameter C2 instead.

Similar to mode 5 except that the input is not filtered, for slightly faster response. Supported in firmware 1.20 and later.

Special mode for BLTouch probe. Supported in firmware 1.21 and later.

Use the Z motor stall detection as the Z probe trigger. Supported in firmware 1.21 and later. There are limitations to stall detection and it is not always appropriate for accurate Z probing however there is a detailed discussion on the forum and some users have had success.

With Duet 2 and earlier Duets: Connect the VCC, GND and OUT pins of the sensor to 3.3V, GND and IN respectively on the Z probe connector, and select mode 1 in the M558 command.

With Duet 3 main board, expansion board or tool board: Connect the VCC, GND and OUT pins of the sensor to 3.3V, GND and IN respectively on an IO probe connector, and select mode 8 in the M558 command. On Duet 3, the IR probe is always in digital mode.

See also DC42's web page on the IR sensor for more on setting up this probe.

See this guide for configuring the strain gauge-based probing on the Smart Effector: Smart effector and carriage adapters for delta printer

Connect as shown in the RepRapPro Ormerod 1 wiring instructions, using the table above to translate between expansion connector pins and Z probe connector pins if necessary, and select mode 1.

Connect as shown in the RepRapPro Ormerod 2/Huxley Duo/Mendel wiring instructions, using the table above to translate between expansion connector pins and Z probe connector pins if necessary, and select mode 2.

If not using JohnSL's trinket board: Connect the FSR(s) in parallel, between +3.3V and the IN pin of the Z-probe connector, and connect a potentiometer or fixed resistor between the IN pin and the GND pin. Select mode 1. Choose the value of the fixed resistor to give reliable triggering. With firmware 1.16 and later it is possible to connect the FSRs between IN and ground instead, and the fixed resistor between IN and +3.3V, if you use the I1 parameter in the M558 command.

If using JohnSL's trinket board: Connect its Vcc, Output and Ground pins to 3.3V, IN and GND on the Z-probe connector respectively and select mode 5.

Connect it between the STP and GND pins of the E0 connector and select mode 4. If it is a normally-closed microswitch, then with version 1.15 or earlier firmware use M574 E0 S1 to select active high trigger level. For normally-open contacts (not recommended), send M574 E0 S0 instead. With 1.16 or later firmware, include parameter I1 in the M558 command if you are using a normally-open switch.

Most Piezo kits come with a number of sensors that connect to a small controller board. The controller board connects to the Duet. See these threads for general advice wiring up and configuring Precision Piezo sensors:

https://www.duet3d.com/forum/thread.php?...

https://www.duet3d.com/forum/thread.php?...

Duet 3, Duet 2 Maestro, or revision 1.04 or later of Duet 2 WiFi or Duet 2 Ethernet: you can connect the output of the sensor directly to the Z-probe IN pin.

Duet WiFi/Ethernet revision 1.03 or earlier, and Duet 06/085: Connect the output wire of the sensor to the cathode of a diode, and the anode of the diode to the Z probe IN pin. The diode should preferably be a small-signal Schottky diode such as BAT43 or BAT85, but a small signal silicon diode such as 1N4148 works for some people.

All Duets: Connect the sensor ground wire to a ground pin on the Duet, and the sensor's + power wire to a suitable voltage (typically to VIN because these sensors usually need between 6 and 30V power).

Select mode 5 (P5) in the M558 command, also include parameter I1 in the M558 command. In the case of RRF3 the I1 to invert has been replaced by adding a ! in front of the pin name in the M558.

Connect the sensor output wire to one end of a resistor (call this R1), and connect one end of another resistor (call this R2) to GND on the Z-probe connector. Connect the free ends of R1 and R2 together and to the IN pin of the Z-probe connector.

For Duet WiFi and Duet Maestro: The values of R1 and R2 should be chosen so that about +3V appears at their junction when triggered. If R2 is 10K, then suitable values of R1 are 30K if the sensor is powered from +12V, and 68K if it is powered from +24V. If you are using the Duet Maestro or the Duet Ethernet/WiFi revision 1.04 or later, the resistor values are less critical and you can use 10K for both.

For Duet 3 and 3 Mini: all IOx.in inputs have a 27K pullup resistor to +3.3V, therefore the value of R2 must be low enough to defeat this. We suggest R2 = 2.2K. Then the value of R1 should be 4.7K to 6.8K if the sensor is powered from +12V; or use 10K to 15K if the sensor is powered from +24V.

Connect the sensor ground wire to Duet ground, and the sensor's + power wire to a suitable voltage (typically to VIN because these sensors usually need between 6 and 30V). An always-on fan connector can be used for this, but make sure you get the polarity right.

Select mode 5 in the M558 command.

See also: BLTouch Troubleshooting

NOTE: CHECK YOUR WIRING! If using a clone BLTouch, or one supplied with a manufacturer's kit, the wiring colours may not match those listed below, which are correct for genuine BLTouch from www.antclabs.com.

For example, recent BLTouch kits for Creality printers use a cable with different colours and wiring. For these, check your wiring based on the following chart (see genuine BLTouch image on right):

	GND (Left)	+5V (Left mid)	Control (Middle)	GND (Right mid)	Out (Right)
Genuine BLTouch	Brown	Red	Yellow	Black	White
Creality kit	White	Black	Yellow	Blue	Red

Connect the BLTouch to a PWM-capable IO header.

For Duet 3 MB6HC, use IO_4, IO_5 or IO_7. For more information on pin header capability, see Duet 3 Mainboard 6HC Hardware Overview

For Duet 3 Mini 5+, use IO_1, IO_2 or IO_3. For more information on pin header capability, see Duet 3 Mini 5+ Hardware overview

Connect as follows:

IO_[n] connector pin	BLTouch pin	Colour
3.3V	-	-
IN	OUT	White
GND	GND	Black + (Brown or Blue)
OUT	Control	Orange or Yellow
+5V	+5V	Red

With older BLTouch (before V3.0), the output is 5V by default. All Duet 3 IO_inputs are 30V tolerant, so it doesn't matter whether you reduce the output of the BLTouch to 3.3V or leave it at 5V.

Connect the BLTouch as follows:

Duet ZProbe connector pin	Duet expansion connector pin	BLTouch pin	Colour
IN		Out	White
GND		GND	Black
	+5V (pin 1)	+5V	Red
	Heater3 (pin 8)	Control	Orange or Yellow
	GND (pin 2)	GND	Brown or Blue

For all Duet 2 WiFi/Ethernet boards prior to version 1.04

If you have the older BLTouch (before V3.0), the output is 5V by default. However, the Z probe input on Duet 2 WiFi/Ethernet boards prior to version 1.04 is not 5V tolerant.

• Either: Connect a 240 ohm resistor between Probe GND and Probe IN.
• Or: Cut the PCB trace on the BLTouch to reduce the output to 3.3V as described in the instructions for your BLTouch version. See https://www.antclabs.com/

All BLTouch V3.0 and later are 3.3V output by default, though can be set to 5V output.

The Z probe input on the Duet 2 WiFi/Ethernet rev 1.04 and later is 30V tolerant, so it doesn't matter whether you reduce the output of the BLTouch to 3.3V or leave it at 5V.

Allocate an unused heater channel to reconfigure as the servo control for the BLTouch. For example, if the E2Heat output is unused, you can use heater 3 which corresponds to the PWM1 connector on Duex. On the Expansion Breakout Board, use heater 6 or 7.

If you have a Duex v0.9 or v0.9a board, check that you have a jumper on the "5V AUX JUMPER SELECT PINS" between the 5V AUX and 5V INT pins. See this thread on the forum for details.

Connect the BLTouch as follows:

Duet ZProbe connector pin	DueXn/BoB PWM connector pin	BLTouch pin	Colour
IN		Out	White
GND		GND	Black
	+5V	+5V	Red
	PWM	Control	Orange or yellow
	GND	GND	Brown or blue

For all Duet 2 WiFi/Ethernet boards prior to version 1.04

If you have the older BLTouch (before V3.0), the output is 5V by default. However, the Z probe input on Duet 2 WiFi/Ethernet boards prior to version 1.04 is not 5V tolerant.

• Either: Connect a 240 ohm resistor between Probe GND and Probe IN.
• Or: Cut the PCB trace on the BLTouch to reduce the output to 3.3V as described in the instructions for your BLTouch version. See https://www.antclabs.com/

All BLTouch V3.0 and later are 3.3V output by default, though can be set to 5V output.

The Z probe input on the Duet 2 WiFi/Ethernet rev 1.04 and later is 30V tolerant, so it doesn't matter whether you reduce the output of the BLTouch to 3.3V or leave it at 5V.

Connect the BLTouch to the Z probe connector as follows:

Duet ZProbe connector pin	BLTouch pin	Colour
IN	Out	White
GND	GND	Black + (Brown or Blue)
MOD	Control	Orange or Yellow
3.3V	-	-
+5V	+5V	Red

With older BLTouch (before V3.0), the output is 5V by default. The Z probe input on the Duet 2 Maestro is 30V tolerant, so it doesn't matter whether you reduce the output of the BLTouch to 3.3V or leave it at 5V.

1. Identify the name of the pin that you connected the control input of the BLTouch to.

• On Duet 3 it is the io[n].out pin, eg io7.out
• On a Duet 2 WiFi/Ethernet without an attached expansion board, it will be one of exp.heater3 thru exp.heater7
• If you have a DueX attached, one of duex.pwm1 thru duex.pwm5
• If you have a Expansion Breakout Board, it's !exp.heater6 or !exp.heater7 ('!' inverts the output, and is needed).
• On a Duet Maestro it is zprobe.mod.

If you use one of these pin names, you will not need to invert the output (except on BoB).

2. The Z probe input pin will be:

• io[n].in pin on Duet 3 eg io7.in
• ^zprobe.in on a Duet 2 (you need to enable the pullup resistor using the ^ character in front of the pin name)

3. In your M558 command, specify probe type 9 and the input pin, for example:

M558 P9 C"^zprobe.in" H5 F100 T2000

4. Create a GPIO/Servo pin index using your chosen control pin:

M950 S0 C"exp.heater3"

In this example we chose to attach GPIO/Servo index 0 to pin exp.heater3 on the expansion connector of a Duet WiFi or Duet Ethernet. On a Duet Maestro you would use C"zprobe.mod" in the M950 command.

5. Set up the probe offsets, trigger height and trigger value in G31:

G31 X20 Y0 Z3.3 P25

In this example the trigger height is 3.3mm (you will need to measure it) and the probe is offset from the head reference point by 20mm in the +X direction.

6. Create a deployprobe.g file (in the /sys folder of the SD card) it should contain the following single command:

M280 P0 S10

7. Create a retractprobe.g file (in the /sys folder of the SD card) it should contain the following single command:

M280 P0 S90

To test the setup with the nozzle maybe a 100mm up from the bed you can check if the trigger signal is reaching the Duet by attempting to extend the pin by using the following command:

M280 P0 S10

If all is well the web interface should report a value of ”0” or "N/A" in the Z probe column when the pin is extended. You can then lightly touch the extended probe pin to check that the value in the Z probe Column changes to “1000”

You can retract the pin again with

M280 P0 S90

the above two commands are also what should be in /sys/deployprobe.g and /sys/retractprobe.g, respectively. Test these are working correctly by sending M401 to deploy the probe, and M402 to retract the probe.

Before trying to home (and smashing your hot end into the bed repeatedly when it doesn't work), conduct the tests and calibrate the Z probe as described here; see Test and calibrate a Z probe

Important: In the M280 commands in the following, leave out the I1 parameter if the BLTouch is connected to a servo output on a DueX board.

1. In your software config.g file input the following G-Code commands to allow the setup to work:

M307 H3 A-1 C-1 D-1

M558 P9 H5 F100 T2000

G31 X0 Y0 Z0 P25

• Important: mode 9 is supported in firmware 1.21 and later only. If you are using earlier firmware, replace P9 in the M558 command by P5.
• In the G31 command the X and Y are the offset of the sensor in relation to the nozzle (so input your own) the number for Z is the trigger height (read on for this). This is the height that is obtained from reading the height the nozzle is from the bed when the sensor pin contacts the bed and retracts, P is the signal threshold.
• Ensure in your config-override.g file (in the /sys folder of the SD card) does not contain an M307 H3 command that overrides the above configuration.
• In the M280 commands (see below), you must invert the servo signal using “I1” in the M280 commands if you connect the BLTouch servo input to the expansion header pins, but not if you connect the BLTouch servo input to a Duex.

2. Create a deployprobe.g file (in the /sys folder of the SD card) it should contain the following single command:

M280 P3 S10 I1

See the important note earlier about including the I1 parameter or not.

3. Create a retractprobe.g file (in the /sys folder of the SD card) it should contain the following single command:

M280 P3 S90 I1

As for the Duet 2 WiFi/Ethernet with the following changes:

• The M307 line is not required
• In all M280 commands, use P64 instead of P3, and leave out the I1. This applies to the following section too.

To test the setup with the nozzle maybe a 100mm up from the bed you can check if the trigger signal is reaching the Duet by attempting to extend the pin by using the following command:

M280 P3 S10 I1

Then put the Sensor in to test mode by inputting the following command:

M280 P3 S120 I1

If all is well the web interface should report a value of ”0” in the Z probe column when the pin is extended. You can then lightly touch the extended probe pin to check that the pin retracts, the value in the Z probe Column should change to “1000”

The BL Touch will continue to cycle deploy in the test mode, to end the test mode enter:

M280 P3 S160 I1

Test deployprobe.g and retractprobe.g are working correctly by sending M401 to deploy the probe, and M402 to retract the probe.

Before trying to home (and smashing your hot end into the bed repeatedly when it doesn't work), conduct the tests and calibrate the Z probe as described here; see Test and calibrate a Z probe

The Touch-Mi is based on an IR end stop with a metal pin for probing in the z direction. While the probe is documented to run at 5v, it can also be run at 3.3v (this has been confirmed with hotends.fr, the manufacturer of the Touch MI). As such, the Touch MI can be connected to the z probe headers of the duet board as shown below.

Alternately, you can connect the Touch-Mi to a 5V pin (from the PanelDue header or from the expansion header) for VCC and to the E0 endstop for GND and IN (use the outer pins of the E0 endstop header).

The Touch-Mi probe is active low. If connected to the z probe port, the M558 configuration should be like this:

M558 P8 F500 H10 I0 T4000

`H` should be at least 3mm, but during the first runs with a new probe (or after changing out your bed), it is advisable to increase H to a safe diving height. The example sets diving height at a comfortable triple minimum distance, and you can reduce H if you are sure the probing pin won't catch after deploying and/or drag across the bed surface during moves.

Also, set trigger value, nozzle offset, trigger offset using G31:

G31 P500 Xnnn Ynnn Znnn

See the calibration section for a method to determine z offset.

The Touch-Mi is deployment is triggered via a magnet. As this magnet is usually installed so it triggers deployment by hitting X0 or X(max), the probing should be at a distance to X0/X(max). As such, it is recommended your mesh definition happens a bit inside the outer edges of your bed parameters. For a 220x220 size bed,

M557 could look like this for a 6x6 grid:

M557 X10:210 Y10:210 S40

M557, M558 and G31 P... as described here should be added to config.g.

deployprobe.g:

; deployprobe.g
; this is a manual probe deployment by touching the Touch-Mi Probe
; with the magnet  included. 

G91                       ; relative positioning
G1 Z7 F600 S2             ; lift Z relative to current position
G90                       ; absolute positioning
; G1 X0 F1800               ; move X to zero
M291 P"Trigger Magnet" S3 ; prompt for magnet action

retractprobe.g

; retractprobe.g
G0 Z0.5             ; dive to retract probe with magnetic ball bearing

homez.g

; homez.g
; called to home the Z axis

G91                ; relative positioning
G90                ; absoute position
M401               ; deploy probe
G1 X163 Y129 F1800 ; move to middle of bed plus probe offsets
G30                ; home z0
M402               ; retract probe

homeall.z

; homeall.g
; called to home all axes

G91                      ; relative positioning
G1 H1 X-225 Y-225 F1800  ; move quickly to X and Y axis endstops and stop there (first pass)
G1 X5 Y5 F6000           ; go back a few mm
G1 H1 X-225 Y-225 F360   ; move slowly to X and Y axis endstops once more (second pass)
G90                      ; absoute position
M401                     ; deploy probe
G1 X163 Y129 F1800       ; move to middle of bed plus probe offsets 
G30                      ; home z0
M402                     ; retract probe

1. Calibrate nozzle to zero manually (paper test).

2. Set Z to zero (G92 Z0)

3. Lift nozzle by 5 to 10 mm (G0 Z10)

4. Determine probe trigger height (G30 S-1) and note the result shown on the G-Code console.

5. Repeat steps 3 and 4 a couple times to ensure the result of G30 S-1 has acceptable repeatability (variance smaller or equal to 0.03mm). Note the average of these repeated measurements.

6. Set the trigger height in G31 in your config.g

See the connection and configuration guide on the TH3D site: https://support.th3dstudio.com/hc/guides...