Spot Welder 1-2-3 Arduino Printed Circuit Board

Some time ago I wrote an instructable where I explained how to control a spot welder in a sophisticated manner using Arduino and commonly available parts. Many people built the control circuit and I received quite some encouraging feedback.

This is a circuit operating at mains voltage and high currents, so the quality of the build is important to guarantee safe operations. While it is ok to prototype the sport welder using a non permanent setup, if you plan to build and really use this a good PCB will help a lot to achieve both a professional and a safe result.

Please read the first instructable, called Part I for short in the following, if you have not done so already. There is a lot of information there that will not be repeated here.

DISCLAIMER: I am providing some links and suggestions for third party sellers/manufactures purely for your convenience and to anticipate the questions I know will come. I have neither any relationship nor any interest in any of the third parties I mention. They purely worked well for me.

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Step 1: Updated Schematic PCB

I have combined control and power circuit in a complete schematic, where several components are added to the simplified (albeit functional) one in Part I.

These include now fuse and line protection on board, and a buzzer to support producing sounds (a clicking sound when the encoder is rotated and a continuous tone when welding are quite nice). An additional MCU pin is exposed on a connector for firmware expansion or modification in order to add new features (EXT connector), e.g. a temperature or cooling fan control.

Step 2: Board Layout

The PCB is a standard 2-layer layout and in the picture you can see how components have been arranged using the EagleCAD layout software.

I have tried to keep things pretty compact using only one side of the board for components and have separated on board the hot and cold side (jargon for the mains AC and 5V DC voltage circuits). The board is about 60 x 80mm (less than 2.5 x 3.5 inches) so it will fit into a compact enclosure.

TRIAC mounting. Please read carefully the consideration on this in Step 6 of Part I. Concerning wire cross section for the connections to the TRIAC, I have used 1.5 mm2 (AWG 15-16) wire for the wires connecting the A1, A2, and G wire pads to the TRIAC terminals, and 2,5 mm2 (AWG 13) for the wires connecting the TRIAC terminals to the MOT (brown wires marked A in the picture in Step 6 of Part I). Keep these connections reasonably short, there should be no need for them to exceed a length of 20-30cm (8-12”).

Step 3: Getting the PCB

You can order the PCB from your preferred fab house, if you have one. I use JLCPCB (www.jlcpcb.com), and in my view they do an excellent job at a very reasonable price.

I am providing the needed Gerber files in an archive data, so you do not need to be able to use EagleCAD to order a PCB, just update the zip file on the fab house site and you are in business. Other suppliers will work in a similar fashion.

The components needed for this circuit are all pretty easy to obtain. I am anyway providing a BOM for your convenience with links to the sources I used to procure the less obvious ones.

Be careful when you order the Pro Mini. There are several layouts around, but the PCB is sized to fit the packaging of the Pro Mini version shown in the picture in the next step. Other geometries will not fit the PCB’s hole pattern.

The PCB requires the 3W version of the Hi-Link power supply module (HLK-PM01 3W). The 5W variant will not fit.

The JP1 jumper marked PRG must be opened to flash the firmware without removing the Pro Mini from the PCB, and obviously kept closed for normal operation.

Step 4: Downloads

The PCB data files can be downloaded from the SpotWelder 1-2-3 PCB repository. In the REAME file in the repository you will find a table of contents.

Have fun!

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    13 Discussions

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    mpfal

    2 months ago

    Hi
    Thanks for sharing your work, it works very well, but
    "....and a buzzer to support producing sounds (a clicking sound when the encoder is rotated and a continuous tone when welding are quite nice)."
    The buzzer does not work, the D9 output does not signal. Can you help me?
    Thanks

    2 replies
    0
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    mecanicafinampfal

    Reply 2 months ago

    Hi, most likely you have swapped some connection on the transistor or the buzzer. This assuming transistor and buzzer are the right type. Unfortunately I am away with no access to the lab for a couple of weeks, so my suggestion is to double check all connections and polarities. Good luck!

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    claustro

    5 months ago

    The PCB is arrived and I waiting for the new parts. I am having problem understanding the new connections , can you help me?
    1) My HLK-PM01 seems bigger and I can't fit in the pcb holes I am missing something?
    2) MAINS 220V in pin 1 - 2
    3) DSP display pin 3 gnd - 4 5v - 5 a5 - 6 a4,
    4) FSW foot switch pin 20 - 21
    5) PNL pin 7 - 8 - 9 -10 - 11 - 12 rotary encoder manual push button and led?
    6) PRG/JP1 13 -14 ?
    7) EXT 15 -16 -17 -18 ?
    8) TRIAC A1 A2 G and the from A1 And A2 to MOT
    9) Buzzer 19 - 20

    Thank you !
    Andrea

    20190323_091051.jpg
    7 replies
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    mecanicafinaclaustro

    Reply 5 months ago

    1) You must have the 5W version that has a larger form factor, the PCB is made for the 3W version.
    2-9) I don't understand the PIN numbers you mention here, all is as per schematic, the mains connector is marked also "mains" on the PCB. Yes, PNL is the front panel connector for encoder push button and led. You don't need to use the EXT connector, that is for future expansion. Finally, the jumper JP1 marked PRG is to temporarily open the power supply connection if you need to flash the firmware for the MCU without removing it from the PCB.
    I think I will add a note about the required power supply version and the PRG jumper to the instructable.

    0
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    claustromecanicafina

    Reply 5 months ago

    Thank you for answering me.With the tester I managed to understand all the connections ( it seems) The problem , at least for me , is that on the pcb FSW PNL EXT and DSP have not pin numbers. Also on the schematics some pins are numbered from left to right looking at the the pc board ( PNL FSW) while others are right to left ( DSP and EXT).
    In the photo below I made a simple scheme for those dumb like me , can you check it?
    thx

    Also is it ok using a 240 ohm resistor instead the 250 one and 350 vs a 360 ohm?
    A.

    pinout.jpg
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    claustroclaustro

    Reply 5 months ago

    Thank you for answering me, the pins number I am refferim to are the one I indicate in red in the attached photo

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    mecanicafinaclaustro

    Reply 5 months ago

    Hi,
    1) The PCB requires the 3W variant, the 5W I suspect you have is too big.
    2-9) I don't understand the pin numers you use here, all connections are as per schematic. 5), yes, it is the front panel connector for encoder, push button and led. 6) is used to flash the MCU without removing it from PCB, see remark added in the instructable. 7) You don't need to use the EXT connector, see remark in the instructable.
    0
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    mecanicafinaclaustro

    Reply 5 months ago

    Hi,
    1) The PCB requires the 3W variant, the 5W I suspect you have is too big.
    2-9) I don't understand the pin numers you use here, all connections are as per schematic. 5), yes, it is the front panel connector for encoder, push button and led. 6) is used to flash the MCU without removing it from PCB, see remark added in the instructable. 7) You don't need to use the EXT connector, see remark in the instructable.

    0
    None
    mecanicafinaclaustro

    Reply 5 months ago

    Hi,
    1) The PCB requires the 3W variant, the 5W I suspect you have is too big.
    2-9) I don't understand the pin numers you use here, all connections are as per schematic. 5), yes, it is the front panel connector for encoder, push button and led. 6) is used to flash the MCU without removing it from PCB, see remark added in the instructable. 7) You don't need to use the EXT connector, see remark in the instructable.

    0
    None
    mecanicafinaclaustro

    Reply 5 months ago

    Hi,
    1) The PCB requires the 3W variant, the 5W I suspect you have is too big.
    2-9) I don't understand the pin numers you use here, all connections are as per schematic. 5), yes, it is the front panel connector for encoder, push button and led. 6) is used to flash the MCU without removing it from PCB, see remark added in the instructable. 7) You don't need to use the EXT connector, see remark in the instructable.

    0
    None
    mecanicafina

    5 months ago

    Hi,
    1) The PCB requires the 3W variant, the 5W I suspect you have is too big.
    2-9) I don't understand the pin numers you use here, all connections are as per schematic. 5), yes, it is the front panel connector for encoder, push button and led. 6) is used to flash the MCU without removing it from PCB, see remark added in the instructable. 7) You don't need to use the EXT connector, see remark in the instructable.
    0
    None
    claustro

    6 months ago

    WOW great job! THANK YOU very much for your work!. I already ordered some pcb from jlcpcb
    I 'll try to make a neat 3d printed case as soon I'll receive it.