Read gscartsw input from EXT Header via GPIO

MOTIVATION

The gscartsw is an automatic SCART switch with an EXT header that supports reading and changing the current input. This script was written to allow this feature to be used in Linux.

This script will not change the current input but will read the current input, it is written in BASH and has been tested on the latest 32-bit Raspbian (as of 1/1/2025) on a Raspberry Pi Zero W.

CREDIT

• superg for making the gscartsw
• shmups.system11.org for documenting the EXT header pinout

EXT HEADER PINOUT

Pin 1: GND
Pin 2: Override
Pin 3: N/C
Pin 4: +5V
Pin 5: IN_BIT0
Pin 6: IN_BIT1
Pin 7: IN_BIT2
Pin 8: N/C

source

RASPBERRY PI PINOUT

pinout.xyz

BUILD INSTRUCTIONS

• Connect your device's GND to EXT Header Pin 1
• Connect three of your device's GPIO pins to EXT Header Pins 5, 6 and 7
• Modify read_gscartsw.sh to match your GPIO pins, or connect as follows:
  • Connect EXT Header Pin 5 to GPIO 12
  • Connect EXT Header Pin 6 to GPIO 20
  • Connect EXT Header Pin 7 to GPIO 21
• On your device run gpiodetect to determine the name of your GPIO chip
  • If your device's GPIO chip is not named "gpiochip0" then modify read_gscartsw.sh accordingly
• Copy read_gscartsw.sh to a directory on your device
• cd to the directory on your device that you copied read_gscartsw.sh to
• Run chmod +x ./read_gscartsw.sh to make the script executable
• To execute the script run ./read_gscartsw.sh

NOTES

While the EXT header is intended to accommodate a standard 4x2 pin male DuPont header (with the help of a soldering iron), the height of the acrylic top plate on the gscartsw is too low to accommodate standard DuPont wire, I solved this by using wire cutters to reduce the height of the wire side of the female DuPont connector by ~4mm. This was tricky, and I do not necessarily recommend it, but it did work.

WARNING

Directly connecting GPIO pins is only safe if the logic level is 3.3v, which is true of gscartsw v5.2. If you have a different version you should check the logic level by testing the voltage at EXT Header Pins 5, 6 and 7 when a SCART input is active on input 8 (located closest to the SCART output). This will cause each of the pins to be driven high, allowing for easy voltage testing.

SYNOPSIS

read_gscartsw.sh

DESCRIPTION

Simple BASH script to read the current input from the gscartsw. This script accepts no arguments.

This script may return one of two values:

• 0 (Success)
• 1 (Failure)

On success this script will output (to stdout) the currently active SCART input, or zero if no input is active.

Errors are output to stderr.

LICENSE

This software is licensed under the MIT License.