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This page describes the DC powered filament extruder that was designed by MOST.

Note that calibration (described below) requires a GNU/Linux system and reasonable advanced knowledge of hard- and software. In particular, you need to know how to edit a program, how to compile a program for a standalone AVR microcontroller, and how to upload that program to the microcontroller. This page explains briefly how to do those things, but the explanations are not aimed at beginners.

Control Board Assembly

Bill of Materials

• Controller printed circuit board (1)
• ATMega 328p, 32-TQFP (1 - cpu1)
• 100k smd resistor, 0805 (3 - R1, R2, R3)
• 4.7k smd resistor, 1206 (1 - R4)
• 16MHz crystal, HC49/SD (1 - Y1)
• MOSFET, IRLR2905PBFCT, TO-252, 2 pin (3 - Q1, Q2, Q3)
• 22pF smd capacitor, 0805 (2 - C1, C2)
• 10mF smd electrolytic cap, 3x5.3 (1 - C3)
• 5V 1A smd diode, DO-214AC (3 - D1, D2, D3)
• Two post screw terminals, 0.2" pitch (3 - P8, P10, P13)
• DC-DC power supply, 7-28V (1, PSU1)
• 2x3 0.1" pitch pin header (2 - P14, P15)
• 2x3 shrouded 0.1" pitch pin header (1 - P12)
• 1x2 0.1" pitch pin headers (6)
• 1x3 0.1" pitch pin headers (2)
• 1x4 0.1" pitch pin headers (3)
• OPTIONAL 1 pin for access to ATMega pins 11, 19 and 26

Assembly

The control board requires careful soldering. Ideally, a reflow oven would be used (a toaster oven can be used if proper care is exercised). Since the many of the components are surface mount, hand soldering is challenging. The following assumes the solder will be reflowed.

1. Set the DC-DC power supply output voltage to 5V. This MUST be done before soldering the DC-DC power supply to the control board. Attempting to set the voltage after it is soldered in place will destroy the ATMega AVR.

2. 

   

   Note that components will be soldered on both the back and the front of the board.

3. 

   Populate all the SMD components on the front of the board with solder paste and reflow the solder.

4. 

   Populate the back of the board with through-hole components.
5. Build and flash the controller's firmware (here).
6. Mount the board on the extruder's frame (there is no mounting board designed, yet).
7. Connect the various components to their respective labeled pins on the controller board (LCD screen, encoder, heater, etc.)
8. When the sensor board is installed, it's communication cable will connect to the icsp header on the controller board.

Sensor Board

Bill of Materials

• Sensor printed circuit board (1)
• AMS-Taos TSL1406R linear sensor array (1)
• Atmel ATTINY45-20SU 8 pin SOIC (1)
• 133-150 ohm SMD resistor, 1206 (1)
• 2x3 shrouded pin header (1)
• 1 x 2 pin header (1)
• 28-30 AWG solid copper wire (for TSL sensor)
• 3mm red LED and patch cable with 1x2 female pin housing
• 1m length of six conductor ribbon cable with keyed housings
• M2 x 12mm screw (2)
• M2 washer (2)

Assembly

The sensor has pads and holes that are smaller than the typical 0.1" (2.54mm) pitch pin headers DO NOT attempt to use a standard pin header and drilling out the sensor; they cost $30.

1. 

   Place the SMD components and reflow. Solder the 2x3 and 1x2 pin headers to the front of the board.

2. 

   Solder short pieces of copper wire into the back of the board and solder the TSL1406R sensor array to the copper wires..
3. Build and flash the firmware to the sensor's AVR (here).

4. 

   Install the LED in the shroud with epoxy.

5. 

   Install the sensor in the printed shroud with two M3 x 12mm screws and washers.

How to calibrate the DC filament extruder

This requires a GNU/Linux system and reasonable advanced knowledge of hard- and software. In particular, you need to know how to edit a program, how to compile a program for a standalone AVR microcontroller, and how to upload that program to the microcontroller. This page explains briefly how to do those things, but the explanations are not aimed at beginners.

Overview of the steps

1. Getting dependencies
2. Build debugging firmware.
3. Upload debugging firmware to sensor board.
4. Upload monitoring firmware to an Arduino.
5. Check the sensor output.
6. Adjust the debugging firmware and repeat until output is satisfactory.
7. Upload adjusted regular firmware to sensor board.
8. Adjust the firmware and repeat until output is satisfactory.
9. Upload production firmware to sensor board.
10. Build main board firmware and upload it to main board.

How these steps work

Here is some information on how these steps work.

Getting dependencies

You will need to get the library for your lcd display and put it in the libraries in your sketch book folder. You will need Arduino libraries from our GitHub and put that into your sketch book folder. Here is a link to Arduino libraries [1]. The library for your display may need to be chained depending on what it is doing.

Building firmware

The github repository contains all the sources in the firmware directory. The firmware for the main board is in extruder, for the sensor is in sensor. The code in sensor-graph is for the monitoring Arduino that is used to show the measured data on screen.

If all the requirements are installed, everything can be built using the make command. (Installing the arduino-mk package should pull everything in that you need.) The code in extruder and sensor-graph should also be buildable from the Arduino UI, but that may not work.

Uploading firmware

Firmware is uploaded using ICSP. We use a Beaglebone which connects four of its digital pins and the 3.3V power to the ICSP connector. An avrdude configuration file is required to make this work. Also, the avrdude version from Debian Jessie (and earlier) has a bug that prevents it from working. This has been fixed in Stretch. For an example of how this is done, see flash-bbb and avrdude.conf in https://github.com/mtu-most/franklin/tree/master/server/.

When uploading firmware, the ICSP connector on the board that is programmed must be used. This is the 6-pin shrouded header. The key of the header is always on the side of the power.

We are using a usb connection to connect to the beagle bone so if you are not using a usb connection these commands will not work. You need to move the firmware from the computer to the beagle bone with " scp build-uno/extruder.hex debian@192.168.7.2: " command and than from the beagle bone to the machine with " sudo avrdude -C +avrdude.conf -c bbbmelzi -p atmega328p -U lfuse:w:0xe2:m ". This command will not run if you do not have this [2] from the franklin repository. You can put that on the beagle bone with this command " scp avrdude.conf debian@192.168.7.2: ".

Running the monitor program

For this, the computer needs to have python-websocketd installed (which requires python-network and python-fhs from the same place). The firmware must be installed on an arduino, and a cable must connect all pins between the ICSP header on the Arduino and the ISCP header on the sensor board. The Arduino does not have a shrouded header; the key should be on the outside of the board. If in doubt, measure which pins have 5V on them.

The server script needs to get the serial data from the Arduino on its standard input. This means the port first needs to be set up, and then it must be given to the server:

 stty -F /dev/ttyACM0 115200 raw
 ./server < /dev/ttyACM0

Then use a browser to go to http://localhost:4567/. You should see a graph of the sensor's measurement.

Running the spy program

For the second step, the output of the regular firmware must be monitored. This is done with the sensor-spy program. It is loaded on an Arduino similar to the sensor-graph program, and it outputs the last received value of the sensor to the serial port.

To use it, simply view the output of the serial port with:

 cat /dev/ttyACM0

When moving a piece of filament through the sensor, it should change its value.

What to change

The senor firmware has two settings defined near the top that need to be changed depending on your build. They are called SKIP and DELAY. The ouput from the sensor should be approximately horizontal. In most of the sensor, it is, but near the edges it goes down to zero. Because of this, the edges are not used. SKIP defines how many pixels are skipped on both sides. Note that the total number of pixels is 768, and it measures every 2^EACHBITS pixels, so if you see something happen at pixel 20, and EACHBITS is 5, it's really pixel 20*32=640.

For monitoring, you may want to decrease EACHBITS. Note that the total number of measured pixels cannot be larger than 255.

DELAY is the integration time, in arbitrary units. Set this so the signal is as high as possible, but doesn't overexpose.

The lowest pixel is used as the position of the shadow. But if its value is higher than VALID_LIMIT, it is discarded and no measurement is sent to the main board. So make sure it is above that value normally, and the shadow takes it below that value.

When this is done, the normal firmware should be uploaded. But initially, this is done with one change: the line defining SEND_MAX should be uncommented. That makes the sensor send the maximum value of each measurement instead of the position of the shadow. The sensor-spy program should be used to check if DELAY is good, and if it isn't it should be adjusted.

Once it's good, the SEND_MAX line should be commented out again and the final version of the firmware should be uploaded. The sensor-spy can be used again to check that everything works well.

scp firmware.hex debian@athena-11.local:

make make MONITOR_PORT=/dev/ttyACM0 BOARD_TAG=mega2560 upload sudo avrdude -C +avrdude.conf -c bbbmelzi -p attiny25 -U flash:w:firmware.hex:i stty -F /dev/ttyACM0 115200 raw