#cetus3d

Sensor

It all starts with the sensor. Most applications rely on either an inductive sensor or a mechanical switch. The problem with inductive sensors, however, is that they rely on voltages from 6 - 36V. This voltage is not readily available on the Cetus, it’s all 5 Volt. After reading some forums and paging through Aliexpress, I found a sensor that could work, the 3D Touch sensor. 

This sensor combines two things

Actuator to drop a pin

Sensor to sense touching the bed

It needs the following connections

3-pin: Brown (-, GND) Red (+5V) Orange (control signal)

2-pin: Black (-, GND) White (Z min)

The actuator is triggered by a PWM signal on the three pin connector where the duty cycle determines the functions

3% - Push pin down

7% - Push pin up

8.4% - Self Test

10.6% - Alarm Release

5.5% - M119 Test Mode

Based on the image show earlier we have two port on the tinyFab CPU that we can use

Port 1.18 - This is connected to the second header on the extruder board.

Port 2.13 - This is attached to the door check on the mainboard

So I started with the easy stuff solder a socket to the mainboard for the door check like so

Then came the next challenge connecting the actuator. I hoped life would be easy and I could just connect the three pins to the auxiliary connector on the extruder. As can be seen, by the diagram, there is a transistor attached to pin 1.18 that pulls the signal low on a high from a pin. This meant that I needed something to make the signal go high against the GND pin. TinyFab suggested using a 10k resistor between 5V and the signal. Now I got the right signal between GND and the Signal pen. The only minor issue was that setting the pin to 3% resulted in a 97% duty cycle. By reverse logic setting it to 97% got me a 3% duty cycle and I could trigger the actuator. This is how I eventually modified my extruder board to get the right connections to the auxiliary connector.

The pins on the left are from top to bottom:

Signal (connected to 5V with 10k resistor)

GND (from Pin 3 of the Fan connector)

5V

Putting everything together and connecting the actuator to the extruder board it looks like this.

Configuration

There are three things that need to be setup in the config.txt file. First the servo, this controls the up and down movement of the pin. Modify the following lines in your config.txt file:

switch.servo.enable true switch.servo.input_on_command M280 S97.0  # 100 - 3% switch.servo.input_off_command M280 S93.0  # 100 - 7% switch.servo.output_pin 1.18 # Pin connected to the aux-port switch.servo.output_type hwpwm       # H/W PWM output settable switch.servo.pwm_period_ms  20      # Default is 50Hz

Make sure that there is no other reference in your confiuration file to pin 1.18

The second part is are the leveling settings:

leveling-strategy.three-point-leveling.enable         true           # leveling-strategy.three-point-leveling.point1         38,0       # first probe point  leveling-strategy.three-point-leveling.point2         175,0      # second probe point leveling-strategy.three-point-leveling.point3         175,180  # third probe point leveling-strategy.three-point-leveling.home_first     true             leveling-strategy.three-point-leveling.tolerance      0.03            leveling-strategy.three-point-leveling.probe_offsets  37,0,0 # based on the bracket          leveling-strategy.three-point-leveling.save_plane     false          

The final part are the z-probe settings. That determine what pin is connected to the switch.

zprobe.enable                                  true zprobe.probe_pin                               2.13 zprobe.slow_feedrate                           5     zprobe.fast_feedrate                           100   zprobe.probe_height                            10  

Most of these settings are already in the confix.txt file, you will need to modify and uncomment based on the above settings

Bracket

To mount the 3D Touch sensor to the extruder assembly I designed a bracket. This can be downloaded from Thingiverse. I printed this using 0.1 layer height and 0.2 mm nozzle. You will need 2 10mm M3 bolts to mount it on the extruder assembly and 2 10mm M3 to mount the sensor to the bracket. The end result should look something like this:

Calibration G-Code

Now that we have the sensor mounted and hooked up to the door connector and the modified auxiliary port on the extruder board we can test if everything is working. Upon startup of your printer the sensor will light up and do a self test. Use the following commands to test the up and down movement of the pin

M280 S97 - Pin up M280 S93 - Pin down

When the pin is in the down position it should be lower than the nozzle on my printer the triggerpoint of the sensor if 0.5mm higher than the requested nozzle height. To check do the following:

Home axis: G28

Drop pin: M280 S97

To go center (based on offset of sensor): G1 X52 Y90

Now move the extruder downward until the sensor is triggered (If the sensor is not triggered before nozzle hits the bed you may need to add a washer between the sensor and the bracket.

Get a reading on the Z-Height and make a note: M114

Now you can add the following code to your slicer:

G28 ; home all axes M280 S97 ; Pin Down G32 ; Level Bed G1 X52 Y90 ; Go to center G30 Z0.5 ; Set sensor offset <-- use value seen at step 5 of the previous process M280 S93 ; Pin Up

Hardware installation

This is the simplest part. Disconnect printer, open the case, carefully remove existing CPU and put the tinyFab CPU in place. Be careful to have the orientation correct. It should look something like this:

Software setup

Download the following

Latest Smoothie firmware (the CPU comes pre-installed with the Smoothieware, but always better to get the latest)

Cetus config.txt file

Plug the printer into USB and turn on. You should see a removable drive appear, out the firmware file and config.txt file here. Restart the printer by powering off and on. This will upgrade the firmware and start using the config.txt for control of the printer.

The config.txt file needs to be adjusted to your printer. Make the following changes: 

gamma_max: set this to the nozzle height in Cetus Studio

uart0.baud_rate: set this to 250000 for faster communication

Unmount the drive and restart the printer.

Calibrate nozzle height

I found the nozzle height in Cetus Studio not to be correct when starting to print with the tinyFab CPU, so I followed this procedure to set it correctly

Connect the printer through USB to either Simplify 3D printer control or repetier-host. Open the serial port to communicate directly to the printer and do:

Home axis (G28)

Move nozzle to middle of plate at 10mm above zero (G1 X90 Y90 Z10)

Use the controls in either printer control or repetier-host to lower the nozzle so that you can pass a piece of paper between nozzle and bed without the nozzle catching it.

Set new zero location (M306 Z0)

Store new zero location permanently (M500). This writes the setting in the config-override file.

Home axis (G28)

Calibrate extruder

I used the procedure described here to calibrate my extruder. The setting in the config.txt file is extruder.hotend.steps_per_mm. I ended up with 233 for my printer. Some tips:

Remove nozzle

Remove the setting from config-override before making changes in config.txt

Printer control

As we can no longer control the printer through Wifi, I have chosen to control it with OctoPrint. You need

Raspberry Pi 2/3

SD Card

Then follow the procedure on the site to install it on the SD card and set it up.

My settings

Here are the settings that I currently use for printing with my Cetus3D

config.txt