LAOS Mainboard v05¶

• Table of contents
• LAOS Mainboard v05
  • Choices
  • Buying parts
  • Connectors
    • JST connectors (HPC LS3020 Pro, HPC LS3020 and most small 2-axis lasers)
    • Phoenix/Wurth (expensive but flexible option for DIY machines)
  • Pololu Stepper Drivers
  • Other parts
  • Voltage regulation
  • Building the board
  • Configuring the jumpers
  • Testing
    • Visual double check
    • Power check
      • Power check 1
      • Power check 2
    • Insert the OPTO-Couplers
  • Test firmwareNow you should be ready to load the TestFirmware

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: https://github.com/LaosLaser/Hardware/tree/master/laos-board-rev5 .

For a pdf of the schematics see here: https://github.com/LaosLaser/Hardware/blob/master/laos-board-rev5/laos-board.pdf?raw=true

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

Choices¶

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
- 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.
- 24V transistor output: Q1 and Q2 are two heavy NPN transistors 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. Before mounting a microSD card holder, please read about know issues on the forum!

µSD issues: http://redmine.laoslaser.org/boards/1/topics/689?r=729#message-729

Note that only 2GB and smaller SD and µSD cards are supported by the LaOS firmware at the moment!

Some parts are not (yet) supported in the software and are therefore not neccesary:
- USB connector (J1)
- CAN bus (CAN1, R1, U1, C2)
LAOS_Mainboard_v05minimal
For a minimal setup, see: LAOS_Mainboard_v05minimal

Buying parts¶

(part listing for US customers: http://redmine.laoslaser.org/boards/2/topics/850 )

You will need at least these parts:

Amount	References	Value	Function	Part	Farnell	Farnell price	RS	RS Price
1				Laos mainboard
5	C1, C2, C3, C5, C8	100nF	Decoupling capacitors for diverse parts	100nF Ceramic capacitor, 5.08mm pin spacing	2112751		721-5240	€ 0,07
1	C7	22nF	Input decoupling for the 7805	22nF ceramic capacitor, 100nF is fine too	1141773		721-5268	€ 0,12
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)	€ 0,65	520-1090	€ 1,31
4	C6,C9,C10,C11	100uF	Voltage buffer for VCPU and Pololus	100uF capacitor, voltage rating at least 1.6 to 2 times VMOT	1902932		520-0996	€ 0,28
5	R10, R18, R19, R21, R22	10k	Pullup resistors for the optocoupler inputs and analog input	10 kOhm resistor	9339060		707-7745	€ 0,02
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	€ 0,02
4	R28, R29, R31, R32	330R	Current limiting resistors for the leds in the output optocouplers	330 Ohm resistor	9339418		707-7622	€ 0,02
1	R34	100R	Limiting/protection resistor for the microcontroller's analog input	100 Ohm resistor	9339043		707-7587	€ 0,02
2	R7, R8	2K2	Pullup resistors for the I2C bus	2.2kOhm resistor	9339302		707-7690	€ 0,02
1	J11	MBED NXP	The microcontroller that's the core of the board	mBed LPC1768 module	1761179	€ 49,73	703-9238	€ 49,53
1	J4	MAGJACK	Ethernet connector with magnetics	MAGJACK SI-60002-F	1137981	€ 6,27	741-8477	€ 4,38
1	J11	MBED NXP	Mbed Holder	TE Connectivity 2.54mm 40 Way 2 Row Straight PCB Socket Through Hole Socket Strip	9688862	€ 2,84	509-2925	€ 3,69
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	€ 2,65	685-0788 / 720-6072	€ 2,22
1	D1	LEDR	This led indicates that the stepper drivers are enabled.	Low cost 3mm red led	1045372		708-2753	€ 0,09
1	D2	LEDY	This led indicates the presence of VMOT	Low cost 3mm yellow led	2080002		708-2769	€ 0,11
1	D3	LEDG	This led indicates the presence of a 5V supply for the microcontroller	Low cost 3mm green led	1652494		708-2756	€ 0,11
2	IC1, IC2	KB847	Quadruple optocoupler for the endstops/outputs	Kingbright KB847	2001656	€ 2,04	619-2026
2			Socket for optocouplers, 0.3inch wide, 16 pin		1077315	€ 2,17	402-771	€ 0,18

Connectors¶

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: http://www.pololu.com/catalog/product/1182

We recommend a heatsink with the pololu, as sold here: ultimachine.com and here: reprap.me

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).

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.

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:

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

Testing¶

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¶

--> First remove the MBED, SDCARD, POLOLUs, OPTO-COUPLERS

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.

WRONG JUMPER CONNECTIONS OR BAD SOLDERING CAN CAUSE YOUR COMPONENTS (OR EVEN YOUR COMPUTER) TO START SMOKING AND CAUSE A LOT OF DAMAGE, MAKE SURE YOU CHECK AND DOUBLE-CHECK EVERYTHING BEFORE CONNECTING THINGS

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¶