A spot welder using caps is harder to design than using a transformer. i would suggest using a microwave Tx with the secondary removed and replaced with a few turns of 6-10 mm insulated cable to produce 3-5 volts ac. To control this a SSR is used on the primary and can turn on/off and Pwm for power adjustment using a micro or 555 timer. This is a way to test spot welding and work out the voltage,time and power needed for good welds. With usable specs then the caps and voltage needed to charge and the time for discharge can be calculated. There are many designs on the web but I could provide photos and circuit for a Tx version at least ! Gary  

Spot welding works best at 3-5 volts,anything much higher is dangerous!

Recently, I installed the Pi-OBD module on a Raspberry Pi 4 using the Raspbian Buster September 2019 release. Compared to the old Pi-OBD module installation guide provided on the Diamex website, there are two differences.1. Configuration of the serial interface In raspi-config, the configuration of the serial interface has been moved from Advanced Options to Interfacing Options. Like on the Pi 3, the first hardware serial interface /dev/serial0 (/dev/ttyAMA0) is occupied by Bluetooth on the Pi 4. To make this available for the Pi-OBD module on GPIO 14 and 15, in a command shell type   sudo raspi-config Select Interfacing Options Select Serial - Enable/Disable shell and kernel messages on the serial connection Answer question "Would you like a login shell to be accessible over serial?" with No. Answer question "Would you like the serial port hardware to be enabled?" with Yes. Select Finish to exit raspi-config. If you are asked to reboot, do not reboot yet. In a command shell type   sudo nano /boot/config.txt and in the editor window add the line   dtoverlay=disable-bt Note: You can also use dtoverlay=pi3-disable-bt like on the Pi 3 because these two overlay files are identical. Then save the file and exit the editor.2. New start script for the Pi-OBD module The gpio v2.50 command of wiringPi that comes with the Raspbian Buster September 2019 release does not function on the Pi 4. The wiringPi author declared it deprecated but provides an updated version v2.52 for it on his website. You can either install and use his new version or use the new raspi-gpio command that comes with the Raspbian Buster release instead. In a command shell type   nano ~/Desktop/startobd.sh and in the editor window enter the following lines   #! /bin/sh sudo raspi-gpio set 18 op pn dl sudo raspi-gpio set 23 op pd dl sleep 1 sudo raspi-gpio set 18 pu dh sleep 1 cd /home/pi/<change to the path where hhgui is located on your system> ./hhgui /dev/ttyAMA0 115200 init=AGV Then save the file and exit the editor. Then to make the script executable, type   sudo chmod +x ~/Desktop/startobd.sh After installation of HHGui, the OBD2 diagnostic software can be started by double-clicking the shell script, then. Notes: raspi-gpio parameters: op = output pn = pull none pd = pull down (~50 kOhm resistor) pu = pull up (~50 kOhm resistor) dl = drive low dh = drive high On the Pi-OBD module there is a pull-down resistor mounted or configured for the BIOS=low/Bootloader=high input connected to GPIO 23 because if the input is left open, BIOS is selected. On the Pi-OBD module there is a pull-up resistor mounted or configured for the Reset=low (active low) input connected to GPIO 18 because if the input is left open, no reset is active.

Yannis, I am still awaiting the cad files so am unable to give you a price.  Perhaps we need to wait until the project matures and we can access the final design. There is probably more development in progress for this project. I look forward to the final result.

This is the origin of the project... I will soon post on the lab the board I've developped to control the joysticks and the marquee...Yes you can find on the web this kind of board ready for few euros, but it is not funny. Mine handles the buttons, the joysticks, 2 coin pushers and the marquee...