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jaap, 2016-05-07 11:25

LAOS Mainboard v05

Bare board

This page describes which parts you need to build revision 5 of the LAOS mainboard. The revision 5 mainboard is a completely redesigned version of the mainboard. It is still compatible with the older versions but the layout has changed.

The board is designed in KiCad and all design files are available on github: .

For a pdf of the schematics see here:

To assemble a Laos mainboard some soldering experience is required. Please read the whole page before ordering parts and assembling.


Before ordering the parts a few choices have to be made:
- External stepper drivers or Pololu 1182 stepper drivers. If you are going to use external stepper drivers, you can omit the Pololu drivers and their capacitors (100uF: C9, C10, C11)
- Power source for the mBed: if there is a stable 5V power source available in you laser cutter you can omit the 7805 and bridge VCPU to +5V on U3.
- Connectors: HPC's lasers use JST connectors, the footprints of the connectors also allow for 5.08mm pitch connectors like a Phoenix contact MSTBA on the PCB and MSTB on the cable.
- Switching output: Q1 and Q2 can host heavy NPN transistors/mosfets that can be used to switch external loads. If you don't want to do that you can omit J27, Q1, Q2, R17 and R15.
- SD card or microSD card: since revision 5 there is an option to mount a microSD card holder instead of the full size SD card holder. Where the regular SD card sticks out of the board, the microSD card stays inside the board. The microSD card holder is harder to mount and some microSD cards may not work with the board (SPI support is not mandatory for microSD cards). When in doubt: use the regular one. There are connection issues with the microSD, before mounting a microSD card holder, please read about know issues on the forum!:

Some parts are not (yet) supported in the software and are therefore not neccesary:
- USB connector (J1)
- CAN bus (CAN1, R1, U1, C2)

For a minimal setup, see: LAOS_Mainboard_v05minimal

Buying parts

(part listing for US customers: )

You will need at least these parts:
Amount References Value Function Part Farnell RS
1 Laos mainboard
1 J11 MBED NXP The microcontroller that's the core of the board mBed LPC1768 module 1761179 703-9238
5 C1, C2, C3, C5, C8 100nF Decoupling capacitors for diverse parts 100nF Ceramic capacitor, 5.08mm pin spacing 2112751 721-5240
1 C7 22nF Input decoupling for the 7805 22nF ceramic capacitor, 100nF is fine too 1141773 721-5268
1 C4 1000uF Voltage buffer for the Pololu's, stabilization of Vmot 1000uF capacitor, 5.0mm pin spacing, 10mm diameter; voltage rating at least 1.6 to 2 times VMOT 1855170 (moq 5) 520-1090
4 C6 100uF Voltage buffer for VCPU and Pololus 100uF capacitor, voltage rating at least 1.6 to 2 times VMOT 1902932 520-0996
5 R10, R18, R19, R21, R22 10k Pullup resistors for the optocoupler inputs and analog input 10 kOhm resistor 9339060 707-7745
13 R12, R15, R17, R30, R2, R3, R4, R5, R23, R24, R26, R27, R33 1k Diverse functions: current limiting resistors for the leds, bias resistors for the high current output transistors, voltage divider for the analog input 1kOhm resistor 9339051 707-7666
4 R28, R29, R31, R32 330R Current limiting resistors for the leds in the output optocouplers 330 Ohm resistor 9339418 707-7622
1 R34 100R Limiting/protection resistor for the microcontroller's analog input 100 Ohm resistor 9339043 707-7587
2 R7, R8 2K2 Pullup resistors for the I2C bus 2.2kOhm resistor 9339302 707-7690
1 J4 MAGJACK Ethernet connector with magnetics MAGJACK SI-60002-F 1137981 741-8477
1 J11 MBED NXP Mbed Holder TE Connectivity 2.54mm 40 Way 2 Row Straight PCB Socket Through Hole Socket Strip 9688862 509-2925
1 U2 Hirose DM1B-DSF-PEJ or Molex 502774-0891 SD card holder Micro SD SMD: Molex 502774-0891 Regular: Hirose DM1B-DSF-PEJ 2064063 / 1764373 685-0788 / 720-6072
1 D1 LEDR This led indicates that the stepper drivers are enabled. Low cost 3mm red led 1045372 708-2753
1 D2 LEDY This led indicates the presence of VMOT Low cost 3mm yellow led 2080002 708-2769
1 D3 LEDG This led indicates the presence of a 5V supply for the microcontroller Low cost 3mm green led 1652494 708-2756
2 IC1, IC2 KB847 Quadruple optocoupler for the endstops/outputs Kingbright KB847 2001656619-2026
2 Socket for optocouplers, 0.3inch wide, 16 pin 1077315 402-771


Both 2.54mm pitch connectors and 5.08mm pitch connectors fit in the board. The reference design uses Phoenix MSTBA and MSTB connectors, which are compatible with the sometimes cheaper Wurth elektronik series 351 and 313. The HPC LS3020 (pro) uses low cost JST connectors and a flatcable. The choice is yours, if you want to keep the original connectors you can use the JST connectors, if you want stronger and more solid connectors you can use the larger ones.

Note that the connectors to the stepper motor(driver)s (J9, J18 and J24) have 5 pins. You need usually only 4 of them; when using Pololu's you need the + and - for coil A and coil B. For external stepper drivers you need E, S and D and either + or GND. If you really need both + and GND get PCB headers with open sides instead of closed sides like the ones above because 5 pin PCB headers with closed sides will not fit.

JST connectors (HPC LS3020 Pro, HPC LS3020 and most small 2-axis lasers)

Count Component RS Part No. RS Price Farnell Part No. Farnell Price Comment
1 WUERTH ELEKTRONIK 3WAY PCB connector RIGHT ANGLE 5.08mm 189-6571 € 0,62 1641987 € 0,60 PCB Power connector
6 JST 4 pin PCB connector B4B-XH-A (LF)(SN) 543-2733 € 0,16 1516278 € 0,20 Stepper drivers, Endstop & Laser and I2C
2 JST 4 pin housing XHP-4 353-1636 € 0,07 1516266 € 0,10 For endstop and laser cable (usually provided with laser)
0 JST 2 pin housing XHP-2 353-1614 € 0,05 1516264 € 0,05 To add laser power modulation
10 JST Socket insert BXH-001T-P0.6 353-1591 € 0,04 1516301 € 0,05 To add laser power modulation
1 FFC / FPC connector 718-8772 (straight, untested) € 0,18 1816463 € 0,30 This connector combines X-axis and endstops!

Phoenix/Wurth (expensive but flexible option for DIY machines)

Count Component RS Part No. RS Price Farnell Part No. Farnell Price
1 Phoenix 3-pin Terminal block MSTB 2.5/ 3-ST-5.08 189-6026 € 2,27 3705365 € 2,45
1 Phoenix 3-pin PCB header MSTBA 2.5/ 3-ST-5.08 189-6111 € 0.84 3705183 € 0,88
10 Phoenix 4-pin terminal block 189-6032 € 3,05 3705377
10 Phoenix 4-pin PCB header 189-6127 € 1,04 3705195
0 Phoenix 5-pin terminal block 189-6048 € 4,00 3705389
0 Phoenix 5-pin PCB header (note: closed sides, does not fit!) 189-6133 € 1,45 3705201
0 Wurth 5-pin PCB header, open sides, black 2081466 € 3,09
0 Weidmuller 5-pin PCB header, open sides, orange 733-0399 € 1,25

Pololu Stepper Drivers

Number Component RS Part No. RS Price Farnell Part No. Farnell Price Comment
2-3 100uF capacitor as Voltage buffer for Pololus 520-0996 € 0,28 1902932
2-3 Pololu stepper drivers Depending on how many axes your machine has
4-6 8x1 pin-header socket 495-8587 € 1,25 3419101 € 0,56 You need 2 for each Pololu

The Pololu you need is of the type A4988:

We recommend a heatsink with the pololu, as sold here: and here:

Other parts

Number Reference Component RS Part No. RS Price Farnell Part No. Farnell Price Comment
1 U3 7805 398-697 € 0,23 Power regulation (see below)
1 U1 2x4 DIL socket 402-759 Canbus IC holder
1 U1 65HVD251 CAN chip 662-4321 Canbus IC
1 R1 Resistor 120 Ohm 707-7599 € 0,02 9339116 Can bus termination resistor
1 J1 USB connector 719-9438 1642033 Usb Host connector
1-2 Q1, Q2 TIP 110 485-9648 9294201 High current outputs

Voltage regulation

If your laser does not have a good 5V power supply built-in, you can add this 7805 power regulator. Note that it will get very hot if you feed it a high voltage. Anything between 7 and 12 volt should be ok. You can use a left-over power adapter to power the board.

The HPC series have a 5V power output built-in.

Building the board

Collect all the parts, put on your favorite music and heat up your soldering iron.
First solder the SD-card connector; it's recommended to use a fine tip for the small legs of the connector. (The pictures are a tiny bit different from the actual rev 0.5 board because this was a pre-production version).

SD card mounted

It's usually the easiest to solder the low parts first; in this way when you put the part in the board and flip it over the part will stay in the board because it lies directly on the table. If other parts were higher the part would fall out.
The lowest part here are the resistors, followed by the leds, ceramic capacitors, jumpers, connectors, electrolytic capacitors and finally the 7805 and large transistors.

Resistors mounted

Pinheaders, ceramic capacitors

Finished board

If you use external stepper drivers you need to make 4 bridges. Refer to the "External stepper driver" drawing on the PCB.

Refer to the following image for the correct orientiation of the flatcable connector:
Flatcable connector mounting

Configuring the jumpers

  • J28: Vout for the high current outputs. This configures what is connected to Vout on J27. This can either be +5V; the stabilized 5V output, or VCPU; the unstabilized VCPU input where the +5V is derived from.
  • J43: Endstops: 3 options: +5V (stabilized 5V), VMOT (from the VMOT input) or VCPU (from the VCPU input)
  • J40: VMOT/VCPU bridge: bridge this jumper if you want to use the same powersource for VMOT and VCPU
  • J7, J16, J22: microstepping: with these solderbridges the microstepping setting can be configured: the default is 16: all bridges connected. If you want something else you need to carefully remove the existing connection between the pads with a sharp knife or a Dremel. Refer to the table on the underside of the PCB for the settings.
  • J12, J19, J25: GND connection for the stepper motor connectors; these bridges are connected by default. If you don't want GND on pin 5 of J9, J18 or J24 remove the connection between the pads.
  • J3: CPU power from USB. You don't want this.
  • J41: O1 Source: dependent on what you want: laser enable of laser on
  • J42: O2 source: dependent on what you want: exhaust enable or laser PWM


Visual double check

Check your board without power, to see if everything is al right
  • Visually check all solder joints. If you're not sure if there is an accidental bridge: test it with a multimeter (continuity check or resistance).
  • Check all soldered wire-bridges and jumper settings

Power check


Power check 1

  • Apply power (CPU and motor). If you have a lab-powersupply with current limiting, use that; set the current limit to about 0.3A.
  • Now check the voltages on the pins of the MBED (5V on pin 2,9 and 10, no voltages on other pins)
  • Check Vmot (usually 24V) on the Pololus
  • Check ground connections on Pololus (by measuring between 5V and those pins)

Power check 2

  • Disconnect power
  • Insert the MBED (with USB connector towards network connector)
  • Connect the MBED to your PC or USB hub with the USB cable
  • Check all 3.3V logic supplies to:
    • Pololus
    • Opto-couplers
    • SD-card

If you are absolutely sure all power connections are OK, install the other components and proceed with the functional tests.


Insert the OPTO-Couplers

The KB847 chips have a tiny line on one side. With the notch on the bottom, this is the right side of the chip. So for both optocouplers the line is on the side of the 7805.

Put the Opto-coupler IC's in place, and the CAN chip and test again. Place a (max 2GB) SD card.

Test firmware
Now you should be ready to load the TestFirmware

Updated by jaap about 8 years ago · 35 revisions