DC-DC Converter for Raspberry PI powered by 12 volt automotive power

Question

I have a basic understanding of electrical systems and want to verify my findings before I commit to buying the component or frying my hardware.

The power supply: Product & Manual.pdf

Currently the plan is to connect this to my vehicles power (Ground & 12v) along with the ignition wire on the left side of the DCDC Converter (per manual). The right side of the DCDC Converter will connect to the PI's GPIO pins (2 and 6). PSW from the DCDC Converter will connect to another GPIO pin (??) when a script on the PI detects is closed, will issue a halt command.

1. Is what I have above correct?
2. What pins should I use for the PSW from the DCDC Converter?
3. Do I need to do anything with pin 1 (3.3v)? I see other posts talking about it but I'm unclear what it does, or if its needed.

Answer 1

1. Powering the Pi with 5volt through pin 2 will work. Note however that this will bypass the poly-fuse on the Pi. The power-supply you are planning to use has a 10A fuse, but that's a lot more that the 1.1A fuse the Pi has. Personally I would just solder the micro-usb to the DCDC output, and connect it the official way. But it up to you.

2. Easiest would be to connect in to a ground pin and an input pin with a pull up resistor. So pins 13&14, 19&20 or 25&26 (don't use 9&10). The broadcom chip on the Pi has internal pull-up resistors. So no need for any external resistors. The pull-up will give a constant high signal on the gpio pin, until the PSW closes the connection between the pin and the ground-pin, pulling it to a low signal.

3. don't connects the 3.3v line. The Pi itself will create the 3.3v for the 5v input.

PS I though that board was a bit overkill, but the HARDOFF feature is very nice and useful.

PSS. sample python code for doing the shutdown, when psw pins are connected/shorted

#!/usr/bin/python
import RPi.GPIO as GPIO
import time
import subprocess

GPIO.setmode(GPIO.BOARD)

GPIO.setup(26, GPIO.IN, pull_up_down=GPIO.PUD_UP)

while True:
    pswState = GPIO.input(26)

    if pswState == False :
        # psw pins connection is closed
        subprocess.call("halt", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

    # wait 1 second
    time.sleep(1)