Here we have a Pi4, a Waveshare 10.1 DSI, a countdown timer and some relays.. not pictured is a usb rotary encoder.
Power is delivered by the stock harness to an aftermarket Metra harness that can disconnect easily from my setup. Constant power keeps the relays and the timer on standby. When the key turns on, the timer relays power to the PD charger then supplies 5v to the pi - at the same time, the key also switches a relay that is connected to a GPIO and a GND on the pi. The pi monitors this GPIO pin via script, when it is pulled low the pi will be allowed to boot. When it is pulled high (the key is turned off) the pi will initiate a proper shutdown. The timer is set so that when the key is turned off, it will countdown 15 seconds to allow the pi to shutdown completely - after which it will cut power to the pi so theres no draw from it.
Another relay is switched by the dimmer wire, this relay is connected to a GPIO and GND and is monitored via script. When the GPIO is pulled low the display dims to 10%.
I found that when the backup cameras RCA was connected to the capture card, the pi would not shut down. Somewhere along the RCA, 5V was getting introduced and was passing through the capture card and powering the pi via USB. So as a band aid I put both the signal feed and ground of the RCA into two relays that are switched by the reverse trigger.
Audio is handled by a DSP amplifier that is connected to the pi via bluetooth. The DSP is 50W x 4 and has an subwoofer RCA output. All DSP/EQ functions are controlled by an android app.
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