Move car setup alternative to an issue thread
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Mike Brady
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# From [FnasBas](https://github.com/FnasBas)
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This is based on [this comment](https://github.com/mikebrady/shairport-sync/issues/482#issuecomment-402543454).
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Here's a starting point. I hope it is useful to someone :)
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# Alternative car setup approach
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This is offered in the hopes it will be useful to someone. The background is that, besides all the advantages of WiFi/AirPlay over Bluetooth,
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when travelling my phone is my only internet connection, and I want to be able to share it with other devices.
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Like an iPad or laptop. I may also want to be able to send audio to the car Shairport Sync service from my other devices while
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simultaneously having internet access on them, via the phone.
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So the basic idea is just to turn the table on which device acts as the Access Point for the WiFi. Which works perfectly well.
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The prerequisite is that your carrier/contract allows tethering, as otherwise you won't be able to have your phone act as a WiFi Access Point.
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I also think this is a bit simpler to set up as you don't need to set up `hostapd` and a DHCP server on the Pi.
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The drawback is that you need to do a gesture and tap a button on the phone to make its network discoverable when entering your car.
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## Phone configuration
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Enable tethering on your iPhone with a secure passphrase.
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## Raspberry Pi configuration
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Set up Shairport Sync according to your needs and instructions found elsewhere.
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### Network
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Configure your Raspberry Pi with only one WiFi network. Through experimentation I found that if I was in the vicinity of my home network,
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the Pi would not reliably choose the iPhone's WiFi network even though it was prioritized over the home network.
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And it seems `wpa-supplicant` in general is a bit difficult to get to roam between different WiFi networks once it's decided on one.
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Example of `/etc/wpa_supplicant/wpa_supplicant.conf`
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```
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ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
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update_config=1
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country=SE
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network={
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priority=3
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ssid="My unique clever wifi network name"
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psk="My very secure wifi key"
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}
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```
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### Read only root filesystem
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By configuring your Pi to have a read only root filesystem, you need not ever worry about an improper shutdown of the OS
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causing the Pi to fail to boot. You will also be sure that the Pi always boots to a predetermined state.
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And you will eleminate wear on the SD card completely except for when modifying the system.
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This will result in a very reliable AirPlay service.
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These instructions are a bit old but a good starting point: (https://openenergymonitor.org/forum-archive/node/5331.html)
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In addition to what's laid out there I've also:
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* Added the `/boot` fs to be mounted read-only and modified the rpi-rw/ro scripts and `/etc/fstab` accordingly
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* in `/etc/systemd/journald.conf`, set `storage=volatile`
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* As the `systemd` `ntp` client is hard-coded to use a specific path for its book keeping, I've disabled that and installed `ntpd`
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and set the drift file to `/tmp/drift`
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* Your DHCP client will complain that it can't write its lease to a file. You can work around this by setting it to write its lease
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to a file in `/tmp` or disregard it as it will work fine in any case.
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In my case I do not use a car stereo but go straight Pi>Dac>Power amplifier. So I've also set up EQ with `alsa`, and a relay module to a
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GPIO pin and some scripts that run on session start/stop that turns the power amplifier on and off accordingly.
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But this could turn in to "How I set up my car audio" rather than offering an alternative to [what's currently suggested
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for a car installation](https://github.com/mikebrady/shairport-sync/blob/master/CAR%20INSTALL.md).
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So I stop. ;)
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## Using it
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Make your phone's network discoverable. In iOS 11 there's a shortcut for this – swipe up and hold down on the connectivity section.
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There's a button to turn on Internet Sharing.
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In my experiments the Pi connects almost instantaneously to this network and a few moments later the AirPlay service offered by Shairport Sync
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will become visible.
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## Changing and Maintaining it
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Make your phone network discoverable. The Pi connects. Connect your laptop to the same network.
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The iPhone does not appear to resolve host names from one tethered device to another so you need to `ssh` to the Pi's IP-address.
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There's a number of ways to find the Pi's IP-address:
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* You can check your laptop's IP and try subtracting or adding from the last octet
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* Use a `zeroconf/avahi` browser tool and locate the AirPlay service and find the IP address that way
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* Use `nmap` or other similar utility to scan for the Pi
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`ssh` to the Pi
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```
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rpi-rw
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change stuff
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rpi-ro
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```
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### Further thinking
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Other Apple devices can wake the WiFi Access Point on the iPhone. My conclusion is that this must be accomplished via Bluetooth,
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but Apple doesn't seem to be open spec on this subject as all I've been able to find is that certain devices, when paired with Bluetooth,
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connected to iCloud etc. etc. will offer this functionality.
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Being able to reverse-engineer what Bluetooth communication is actually done in order to turn on the WiFi Access Point on the phone
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would mitigate the drawback of this method, as the Paspberry Pi could be constantly looking for the phone via Bluetooth and
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enabling Internet Sharing that way.
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