Configure raspberry pi wifi by writing to micro SD card

I have a raspberry pi but no external keyboard, mouse or ethernet cable to set it up - but I do have micro-sd card reader. Is there a way for me to just write my wireless internet config straight to the micro-sd card so the raspberry pi will be able to connect to the wifi, and then allow me to ssh in?

The micro-sd card already has Raspbian installed on it.

Solution

Sure.

Put the card in a drive and mount it.
Go to the partition called boot.

Create an empty file called ssh just using:

touch ssh            # Works in Linux/macOS
type NUL >> ssh      # Works in Windows

Create a file called wpa_supplicant.conf with your WiFi settings - be very sure that Windows hasn't added any .txt extension:

country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
    ssid="NETWORK-NAME"
    psk="NETWORK-PASSWORD"
}

Once it works, and you can ssh successfully into the Raspberry Pi, be sure to run:

sudo raspi-config

and permanently enable ssh for subsequent reboots.