Valve board A of the digital Festo valve control (box A, 8 valves). Board size 155 x 124 mm.

• STM32G030 as Modbus RTU slave, isolated RS-485 (ADM2587E), 4-bit DIP address switch, termination jumper, SWD header
• 8 high-side outputs: 1 x VNI8200XP (0.7 A per channel), one output per valve, continuous 24 V (on = open, off = closed)
• Series diode per output (protects the driver from the box's existing hand circuit on the same valve terminal) plus freewheeling diode
• J301 = +24 V to valves 1-8, J302 = 0 V return; wired in parallel to the existing hand wire at each valve terminal
• Online/hand switching: Raspberry Pi -> Modbus -> STM32 (RELAY_ON) -> Q101 -> relay K101. K101 energised = online: the supply of the existing hand circuit (J104 pin 1 -> pin 2) is opened and the driver is enabled. K101 released (Pi off, board unpowered, fault) = hand mode: the box works as before and the driver is locked in hardware (U113 pulls OUT_EN low)
• Status inputs to the STM32: hand mode (U111), 24 V behind E-stop present (U112)
• Bus connector J1 (24 V, safety chain, RS-485) from the Hauptboard, J2 = RS-485 to the next board

Related boards: Ventilsteuerung Hauptboard, Ventilsteuerung Board B (box B, 12 valves). Status: layout routed, not yet built or tested.