LAOS Mainboard v05¶

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.

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

Buying parts¶

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
1	C6	100uF	Voltage buffer for VCPU.	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	U2	Hirose DM1B-DSF-PEJ or Molex 502774-0891	SD card holder	Micro SD SMD: Molex 502774-0891 Regular: Hirose DM1B-DSF-PEJ	9688862	€ 2,65	685-0788	€ 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.

Phoenix/Wurth¶

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

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 I recommend getting PCB headers with open sides instead of closed sides like the ones above because 5 pin PCB headers with closed sides will not fit.

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.

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.

Configuring the jumpers¶

• J28: Vout for the high current outputs
• J43: Endstops
• J40: VMOT/VCPU bridge
• J12, J19, J25: microstepping
• J3: CPU power from USB
• J41: O1 Source
• J42: O2 source

Testing¶

Connecting your lasercutter¶

• PWM (capacitor)