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From the research I did it seems like you want a voltage 12-16V roughly. A 12V car battery would be a great substitute if the price of super capacitors is too much.
The resistor on the top far left is representing the battery tab or whatever you're welding resistance. So that's the place where your two welding probes would touch in otherwords.
The first version of the spot welder I used some N-Channel Mosfets from SparkFun. https://www.sparkfun.com/products/10213 I believe I used 5 or 6 of them in parallel.
The LCD screen libraries can be found from the manufacturer's website. The particular screen I used is similar to this. https://www.sainsmart.com/products/20x4-iic-i2c-twi-lcd-module
Space Farm Rotating Rack SystemView Instructable »
Power Mosfets would work too and would be cheaper. I went the IGBT route to lower the amount of components and connections needed.
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