The main focus of this session was to build the 24V subsystem. The electronics of the machine were powered by an old power supply that took the incoming 240V AC power and reduced it to 24V DC. We're replacing that with a modern switched-mode power supply, and a bank of nine relays will control the machine components. We only needed a single pole relay for each component, but when surplus multi-pole relays were available cheap on eBay, we got those and left connectors unused. The power supply and relays were all mounted to a single DIN rail.

The nine relays have been assigned to the following functions:

1. Main: Controls 220V power to the remainder of the machine. The air compressor will have power whenever Main220 is on, we rely on its own pressure control circuit to turn the actual motor on/off.
2. Vacuum Pump: Power to the vacuum pump.
3. Heater: Contactor which will turn on the 240V, 40A(?) heater element.
4. Vacuum Valve: Connects table to the vacuum tank, in order to pull work piece against the mold.
5. Up Valve: Send compressed air to the "up" side of the frame air cylinder, raising the frame.
6. Down Valve: Opposite of the above, send air to pull the frame down.
7. Heater Forward: Normally compressed air will hold the heater in the back position. This relay control the valve that switches compressed air to push the heater forward.
8. Blow-off: When the work piece is complete, compressed air can be sent to the table to help remove the work piece.
9. Magnets: When active, holds the frame closed.

The bottom row of terminal blocks will be wired to their corresponding components in the machine.

The top row of terminal blocks will be wired to allow control of those components. The first iteration will just have a row of toggle switches for manual control. Later iterations will have some kind of micro controller brain, whether it'll be an Arduino or a Raspberry Pi or something else is to be determined.

Which leads to the question... what switches do we flip, and when? We started brainstorming the machine's work cycle on the whiteboard.

Since this specific machine has never worked in our possession, we can't just write down what it used to do. We pulled up some YouTube videos of similar machines at work, looked at the components in our machine, and made our best guess. We think we have all the major pieces up on the whiteboard but some of the steps are question marks.

For one example: we were evenly divided on what to do once the vacuum forming is complete. Should we activate the blow-off valve before we open the frame, or after? The state machine has "Open" followed by "Eject", but maybe those two should be reversed. There were arguments in favor of each side and we'll just have to try both to see which works better.