LAOS I2C Panel v0.4


We designed a panel with a 2x16 LCD, 4 buttons and a joystick. The heart of the panel is a ATMEGA168-20PU running a small Arduino program. The panel uses I2C communication to the MBED board, but there is also a connection for a standard USB->TTL cable. You can use such a cable to upgrade the program in the Arduino chip.
All the source files of this project are available in the i2c panel project on Github:


The user interface functionality is not implemented in this board, but in the program on the MBED. The on board ATMEGA with Arduino code only receives data for displaying on the screen and sends key press codes via I2C, basically this works as a tiny terminal. The functionality as stated here is just to show what the main LaOS controller board uses it for.

While no job is running:

  • Manual focus, using up and down buttons (for some machines this will mean that the Z-axis is moving, others will move the lens-holder up and down)
  • Moving the head to a specific location (jog in the X and Y axis)
  • Select the current location and make that the origin (x=0, y=0, z=0)
  • Select print job

While a job is printing:

  • Pause current job
  • Resume paused job
  • Cancel current job


We designed our own board and software (Arduino based) to connect the display board to the mainboard (via I2C interface). The schematics (in KiCAD) are located [here].

Most important parts:

Full part list is available in GIT

  • 16x2 LCD Display, RS stocknummer 532-6408
  • ATMega168P-20PU, RS stocknummer 696-2430
  • 4 Pushbuttons
  • 1 Joystick button
  • and of course, the PCB

Bill of Materials

Number Component RS Part No. RS Price Farnell Part No. Farnell Price Comment
1 LCD display, green, 16x2 characters 532-6408 / 720-0207 / 5326436 € 5,14
1 OR LCD display, blue, 16x2 characters 5326436 € 7,23
1 ATMega168P-20PU 738-0375 € 5,22 1636933 € 4,81
1 OR ATMega328P-20PU 696-2260 / 1715487 - either 168 or 328, not both
4 Thru hole tactileswitch12x12x7.3mm 378-6763 € 0,46
1 PCB Stick switch, 4 dir + centre push 516-316 € 2,46 1435775 € 2,47
1 Ceramic resonator THT CSTLS 16.00MHz 526-6154 € 0,56 1448129 € 0,46
1 28way low profile DIL socket,0.3in pitch 801-768 € 0,24
1 100uF capacitor 711-0703 € 0,03
2 100nF capacitor 721-5240 € 0,07
1 10K resistor 707-7745 € 0,02
1 36 way straight header,7mm top 3mm below 251-8632 € 1,034 1824426 € 0,92
2 BS270 1017689 € 0,15
1 Kingstate KPEG242 buzzer 1502726 € 2,03
3 plastic buttoncap black 378-6943 € 0,11
1 plastic buttoncap red 378-6937 € 0,11
1 JST 4 pin PCB connector B4B-XH-A (LF)(SN) 543-2733 € 0,16 1516278 € 0,20 I2C (optional)
1 lasercut cardboard
1 PCB E218213 € 7,50 Available from LaOS (see WebShop )

Mechanical construction

  • PCB is positioned directly under the display
  • I2C communication is through a 4-pin flatcable with pin-header
  • A 6-pin (USB->TTL) connector is available for easy updates of the Arduino
  • 4 standard pushbuttons
  • 1 Joystick button (with 3D printed key cap)

The design files for a frontpanel and buttons can be found here: [Frontplates]
Peter Uitenhoven posted a Joystick thumb on Thingiverse:
Mowi designed a Joystick knob:


The Arduino software on the ATMEGA chip is available on github

The electronics are based on John Crouchley's ATTiny2313 implementation. The Arduino (or Ottantotto) electronics come from Edwin Dertien.

Relevant Arduino libraries:

I2C on the Mbed: Have a look at this very enlightning drawing!

For debugging, you can use any PC with a home-made I2C adapter:

Building your own

To make life easier, we sell premade PCB's and this panel as a kit. See the WebShop.

The kit contains:

  • PCB
  • ATMEGA168-20PU, pre-programmed with the Arduino bootloader and this I2C program (so you can install it even if you do not own a USB->TTL cable).
  • LCD
  • other electronic parts
  • Buttons
  • I2C wire to motherboard

Parts it does not contain:

  • Laser cut panel. You can make one on your laser, maybe? Probably you want one to fit into your machine, anyway. See below for the panel the MiniFabLab made for its HPC LS3020
  • 3D Printed joystick button. When I design one I'm really proud of, I might include it.

Feel free to make the user interface panel yourself if you prefer. No need to buy stuff if you have an Arduino lying around with LCD and some buttons!


This board has parts on BOTH sides! The display and buttons go on one side, all the other electronic parts go on the other.

Non-display side: the side where it says "LAOS I2C rev 0.4".
  • Start by soldering the the socket for the Atmel IC, making sure the notch is on the same side as the one on the silkscreen legend.
  • Place the resistors. There is only one, that's why it's labeled R2
  • Solder the two 100nF capacitors in U1 and U4.
  • Solder the 100uF electrolytic capacitor with the plus (longer) wire in the hole with square solder pad (U2).
  • Solder in the two BS270 in Q1 and Q4.
  • Solder the 3 pin ceramic resonator (F1)
  • Solder the piezzo buzzer (SP1).
  • Solder the I2C pins. Make sure the 4-pin header matches with the cable you're going to use.
  • Place a regular 2-pin header in P3 and P7 and a 6-pin header in P1 (TTL). Place two 3-pin headers in P4.
  • Now take a 16-pin header and push it with the longer pin ends in the PCB from the bottom (solder) side of the board. The long pins will stick out on the top side of the board. The black plastic of the header in now on the bottom of the PCB. Measure with the display module to see if the pins are long enough to go just through the module. Solder the 16-pin header to the board on the TOP (component) side.
    Front (display side):
  • Place a strong piece of tape or (lasercut) cardboard on the bottom side of the board, covering the part of the board that will be under the display module, so that there cannot be any shortcircuit between the board and the display module. You can use electric shielding tape or gaffer tape.
  • Solder the 4 buttons to the board (not the joystick yet!) with the buttons on the side of the display (solder side).
  • The joystick has a very small dent in the top metal layer. If you put the joystick in, this dent should be on the right side, where there is a small mark on the print. Solder it in.
  • Solder the display module on the back side board, with the black strip of the 16-pin header in between.

Front side of the panel.

Back side of the panel.

Software installation

Installing a bootloader

These instructions are for ATMEGA168P-PU

cd /opt/arduino-1.6.4/hardware/arduino/avr/bootloaders/atmega
avrdude -p m168p -c usbasp -F -U lock:w:0x3F:m -U hfuse:w:0xDE:m -U flash:w:ATmegaBOOT_168_diecimila.hex -U efuse:w:0xF8:m
avrdude -p m168p -c usbasp -F -U lfuse:w:0xff:m

Error message while installing:

avrdude: safemode: efuse changed! Was f8, and is now 0
Would you like this fuse to be changed back? [y/n]

Answer n !

and for the ATMEGA328P-PU

<cd /opt/arduino-1.6.4/hardware/arduino/avr/bootloaders/optiboot
avrdude -p m328p -c usbasp -F -U lock:w:0x3F:m -U efuse:w:0x05:m -U hfuse:w:0xDE:m -U flash:w:optiboot_atmega328.hex -U lfuse:w:0xFF:m

Arduino Sketch

Use a USB=>TTL cable to connect the board to your computer. Install Arduino software. Get "lasercutterpanelv0_3.pde from GIT":

To test your panel, change:

#define DEBUG 0


#define DEBUG 1

Arduino settings: Board: Arduino NG or older with Atmega168

Upload the file to the board. This will give you a welcome text. After the text has disappeared, all buttons should show a number on the screen. The joystick should show 5 different values for each direction and middle push.

If it works, upload the code again with DEBUG 0. The panel is now ready to be connected to the mainboard.

Joystick knob and panel

To integrate your display in the laser, download Monique's design for a knob + display panel:

Control Panel on the HPC LS3020

To accomodate the display you can cut a replacement for the control panel.

The button laser switch was replaced by a toggle for better on/off reference. So the right serial test button could be omitted. Also the lighting switch was removed, now the light is always on. No modifications are required for the cabletree, just connect the wires from the removed switches. The air pump switch was kept as a compressor can be noisy. It is advised to use a shielded cable between the I2C panel and the board. A cutting file (.svg) of this panel is available on miniFabLab.


Previous version:

For links on previous versions and to get started on designing your own display, see the Display-alternatives page.

Cable conn: Preci-dip, RS: 702-0095

display-rev0.4.jpg View (743 KB) jaap, 2013-05-07 21:01

display-rev0.4.jpg View (49.6 KB) jaap, 2013-05-07 21:03

display-back-rev0.4.jpg View (56 KB) jaap, 2013-05-07 21:28