A befriended couple told me that they would like to provide multimedia entertainment for their 3 kids on the backseat of the car when going on holiday or a long road trip. Each kid has a tablet but the storage room on these is not sufficient to store enough content and it would also require storing the same content 3 times. Initially I was inspired by a Raspberry Pi project but to me that has too many disadvantages, the main being risk of corrupting the SD card from unexpected power loss which is very likely when used in a car. But that project did provide me the required functionalities:

USB port; to connect storage media and mount them
DHCP; to give connected devices an IP address
Router: to route traffic to and from sources and devices
DLNA server; to provide access to media for connected DLNA capable devices

So I looked further for a solution that provided these functionalities, would require less or no tinkering and be more robust than a RaspberryPi in these circumstances. While searching the internet for a solution it occurred to me that current router-access points have all the necessary functionality. So that's what I ended up with.

Step 1: What You Need

This is the shopping list. Total cost are around € 190,00

A router access point. I used the Netgear WNDR3700v5 because it has all the right features for this particular use. The product is on the market since 2009 and the firmware is revision 5. It is the stereotypical 'proven technology'.
A sizable USB drive. I used a 128GB Sandisk Ultra Fit because it is small and sticks out very little when inserted, reducing the risk of damage. Also performance is excellent.
A 12 Volt DC/DC car adapter. I used [P.SUP.SMP36-HQ] HQ Universal car adapter 36W because it provides enough power and stabilises to 12V exact.

You will also need a PC or Tablet to logon the router to make the necessary configurations and to copy your media files to the USB drive.

Update: Even a 128GB USB drive can only hold a limited number of media files. So we looked for more. And added two more of the same combined with a USB powered 3 port hub.

Step 2: Preparations

Before you proceed, make sure you...

Have the USB storage drive(s) ready.
Have a laptop or PC that can be connected both wired and wireless to the router.

NOTE: Assuming you already know this, I will NOT explain how to connect to a wireless or wired network, nor will I explain how to open your browser and navigate to a certain address.

You need only configure the router. You can find all available settings in the PDF manual. Below are the steps for this particular use, it should take no more than 15 minutes:

configure WAN settings
Make the USB drive shared
Activate the media server (DLNA server)

WNDR3700v5_UM_03Sept2015.pdf
Download

Step 3: Let's Get Started

Switch on your laptop (or PC, whatever you are using)
Switch on the WNDR3700v5 and wait until it is fully started
Disable wireless on your laptop
Connect your computer to the WNDR3700v5 with a cable
Wait until your computer has established the network connection with the WNDR3700v5. The WNDR3700v5 will provide an IP address to your computer, this may take a minute. If a popup shows asking for the type of network, choose home network.
Now, open your browser, you should automatically get redirected to the Netgear Genie page. If not, navigate to www.routerlogin.net. If that doesn't work, navigate to 192.168.1.1
When asked for login, the username is admin and the password is password.

You are now logged into the interface of the router to make your adjustments.

Step 4: Configure WAN Settings

(Screenshot 1) Skip the wizard, choose "No, I want to configure the router myself" and then Next.
(Screenshot 2) Where you see in red the error "not connected", click on "Internet".
(Screenshot 3) Choose "No, I want to configure the router myself" and then Next.
(Screenshot 4) Under Internet IP address, choose static IP address
1. For IP address type in 192.168.2.1.
2. For IP subnet mask type in 255.255.255.0
3. For gateway IP address type in 192.168.2.2
4. Under DNS type 8.8.8.8
Click Apply. The router may restart.
Now disconnect the wire between your computer and the WNDR3700v5.

Wait a minute or two to make sure the WNDR3700v5 has restarted fully.

Switch the wireless adapter of your laptop back on.
Connect wireless to the network with SSID name Netgear33 with the standard password that is on the factory sticker of the WNDR3700v5. NOTE: You need to connect wirelessly, because wired, somehow because of the changed IP settings, you end up in the guest network and from there no settings are available so you would be stuck.
Login to the WNDR3700v5 again as before by going to www.routerlogin.net. If that doesn't work, navigate to 192.168.1.1
After login, you start in Home. It should be like screenshot 5 (no error anymore)

Step 5: Make the USB Drive Shared

Next plug in the USB stick.

NOTE: I used a USB powered 3 port hub to connect 3 USB storage devices. So in the screenshots you see three drives. I you use only one USB storage device you will see only one, obviously.

(Screenshot 1) Go to advanced tab.

(screenshot 2) Go to USB storage and then ReadySHARE. Make sure that the storage is visible under Available network folder

(Screenshot 3) Stay under USB storage and then Advanced Settings. If you click on the link behind HTTP, you should be able to browse to the files and folders on your storage device.

Step 6: Activate the Media Server (DLNA Server)

(Screenshot 1) Stay under USB storage and then click Media Server. Tick Enable Media Server and click Apply.

That's it! Click logout (top right) and close browser.

Step 7: Connect and Play

So, assuming the WNDR3700v5 is now running, take your smart phone or tablet and connect to it wirelessly using the SSID Netgear33 or Netgear33-5G and the password on the factory sticker.

DLNA discovery

Theoretically, from any DLNA capable device that you connect (wirelessly) to the WNDR3700v5, you should be able to play the media files that are on the storage. So you need an app that will discover the DLNA server and play the files on the USB drive. If you already have an app for playing multimedia content, try that one first to see if it finds the DLNA media server and plays the files. If so, you're done, enjoy your portable media hub. If not, read on.

For Android I used GinkoDLNA and VLC, both are available for free in Google's Play store.For Apple devices I used Moliplayer, the paid version works in this setup. On my Windows laptop I used Windows media player. Sometimes it takes a while before the DLNA server is discovered, but after a while it usually appears and then you can connect and play.

Android

GinkoDLNA is an app that excellenty discovers DLNA servers in the network. VLC is a media player. Both apps are free. Open GinkoDLNA and it should give you a list of discovered DLNA servers. You should see here WNDR3700v5 (if you left it unchanged in the configuration). Tap on that and you can browse the files. When you tap on a media file, it will ask you what app to use to play (render, in DLNA terms) it. Choose VLC or any other player that you may use.

Apple

Apple is a bit tricky because Apple likes to bind you to Apple protocols. However, Moliplayer seems to be able to discover the DLNA server and play the media files. However, it did take some time and multiple tries to get it to work. The basis idea is the same as for Android, find the DLNA server, browse the files, tap on the file you want play.

Step 8: Additional Stuff

Below are some additional thoughts that went into this project that led to the choices of hard and software. I hope this tutorial was useful and enjoyable.

About the concept

Isn't there already something out there off the shelf that does the same? Actuallu yes, there is something called Mediashare from IOGear. That device costs about the same as this setup but without storage. It does have a built in battery so that gives you a little more freedom.

About the router

This instructable explains what to do based on the specified router. However, most routers contain similar functions nowadays, so it may be that you have another make and model lying around that is also usable. You should be able to find the functions based on the common names used. If you are a techie you may conclude that the specs of this WNDR3700v5 is a bit overdone for this use. You're right. The reason for this is, that after the holiday, this router will be used in the home as what it was intended for.

About the 12V DC/DC adapter

It was actually some sort of a challenge to find a good 12 Volt power supply for the car. Contrary to what you may think, the voltage in your car is not 12 Volts but more likely 14,5 Volts. The actual voltage depends on the charge state and quality of the battery, the temperature and the load on the battery. Now, the most commonly used (and cheapest) electronic parts to stabilise a DC voltage require a minimum of 3 Volts difference between input and output. This type of component would not be able to stabilise the output to 12 Volts from 14,5 Volts. So you need more expensive parts that can stabilise with a minimum of 1,5 Volts difference, or apply some electronical tricks to first crank the Voltage up and then regulate down again. I chose this product based on it specs for providing stabilised 12V. Before using it I measured the output voltage to make sure it supplied a steady 12 Volt under different circumstances.

About DLNA

To be able to use the widest range of devices to connect to the media hub, I chose to use DLNA. This is a construction or set of rules that make it easy to stream media on a network. When playing media with DLNA, there is always a Server, Controller and Renderer as software functions. The strong point of DLNA is that these three functions can, but do not need to be, on the same device. The server function will let you browse through your listing. The play, pause etc. buttons are the controller function. The screen, speakers and hardware behind it are the renderer function. If for example, you play a Youtube video from your smartphone through Chromecast on your TV, the phone is the controller, the Chromecast together with the TV is the renderer and Youtube is the server. In this instructable, the router act as server, the connected devices are both controller and renderer.

About media

DLNA servers do not care what type of media you want to play, it only serves to make it available to a connected client device. Whether or not a file can be played depends on the renderer software, like the app on a smartphone or tablet. Basic rule is that if you can play a file from the device itself (downloaded onto it), you can play it via this set up. However, sometimes less common types of files are not displayed in a listing of available files by the server. It may also be that additional functionality is available on top of the basic DLNA functions. Everything depends on how strict the software developer adheres to the DLNA specifications and / or wants to add additional functionality.