Using MOSFET to switch dual power supply with common ground as a PWR/GND DPST switch for each power line

Question

I have started a new project, an automatic firing system for fireworks, powered by 2 lead-acid batteries (12V). The batteries are connected in series with a common ground (GND), so the power distribution board has 3 power terminals (+12V, GND, -12V).

The firing system will include more firing channels controlled by a STM32 board, so all the MOSFETs used will be controlled by 3.3V signals. Also each channel will have 2 outputs/terminals, NEGATIVE and POSITIVE.

Because of the project requirements, the IGNITION_POS and IGNITION_NEG should be able to handle 4 different states based on the 2 switches (STM32 GPIOs):

• Both terminals ON -> IGNITION_POS: +12V and IGNITION_NEG: -12V
• Both terminals OFF -> IGNITION_POS: GND and IGNITION_NEG: GND
• Positive terminal ON -> IGNITION_POS: +12V and IGNITION_NEG: GND
• Negative terminal ON -> IGNITION_POS: GND and IGNITION_NEG: -12V

I'm unable to find a solution to switch terminals to GND when the state of the MOSFETs is OFF. Also i want to specify that the current through terminals can sometimes be more than 30A, so we can't use a simple pull-down resistor.

For simplicity i attached a schematic which includes simple ON/OFF switches, not the actual STM32 GPIOs.

Can you help me with some suggestions to achieve this behavior ?

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

For transferring signals from STM use 4 opto-couplers.
To pulling terminals to GND use mosfets M2 and M3.
In firmware always turn on M2 delayed after M1 turns off (also other changes of mosfet states) otherwise mosfets get shot-through. Another words use dead-times.

^{simulate this circuit – Schematic created using CircuitLab}