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If you look at the specifications, you can legitimately ask whether digital signage is possible with the Raspberry Pi. The hardware and software support is exemplary and there are inexpensive starter kits. The community is huge, has a lot of experience and you can get easily supprot. The device plays beneath pictures and web sites, Full HD videos and now even works with WLAN.
Nevertheless, in my view, there are some conceptual drawbacks which limit the Digital Signage and Raspberry Pi combination severely, particularly in a network.
First of all, it was designed as a learning computer and not for media player purposes. For example, the network is connected using a USB hub in order to save costs and the overall performance is just satisfactory.
I only list this model for the sake of completeness. The Raspberry Pi Zero has been available since November 2015 for just under 5 EUR. In the variation from February 2017 even with WiFI. The Zero has only 512 MB of working memory and the CPU from the first Raspi model with only one core. Despite the video acceleration, it works much too slowly to be used as a media center or even in digital signage projects.
In the summer of 2016, I ported my garlic-player to the Zero as part of a customer project out of curiosity. It ran and even HD videos played. However, the operation was tough and it was not really fun to administrate the device. As a technology study it was of course impressive for the customer. However, this hardware was not created for serious projects in the field of media.
In June 2019, the Raspberry Pi was released in version 4. The new CPU is much more powerful and the network no longer runs over USB. The performance has been greatly improved overall and the device even runs two 4K monitors simultaneously. Moreover, it even addresses 8GB of main memory in a slightly more expensive variant since May 2020. It seems at first glance with a good heat sinking case, even less problems for use in digital signage projects to give.
Unfortunately, appearances are misleading and a second look reveals some problems. The Raspberry Pi 4 still does not accelerate 4K videos currently (April 2021). Only the LibreElec project manages to play a certain video profile. Otherwise, 4K content stutters unacceptably and and leads to overheating.
To completely address the partially up to 8GB large main memory, it requires a 64-bit operating system. The oficial 64 bit Raspberry Pi OS (formerly Rasbian) has been in the test phase since May 2020. However, the hardware acceleration for videos is completely missing there.
It is true that during one of my tests, an impressive four videos ran almost smoothly at the same time. However, since a processor that gets quite hot bears the main load instead of the video accelerator, this causes questions regarding long-term stability. Apart from the fact, of course, that there is no question of using test operating systems in productive signage projects under any circumstances.
For several months (as of April 2021) nothing significant is happening there, unfortunately. From my point of view, this is sad. In the field of low-cost digital signage projects, the Raspberry Pi 4 could set standards. Being able to display content on two 4K monitors without any problems is unique in the price category.
Usually a CMS operates the network in Digital Signage projects for repeatedly change the content quite promptly. So, the players are centrally operable and should be able to submit logs for play or error statistics. For a media player, this means lots of writing accesses to its internal storage in addition to reading accesses. A standard Raspberry Pi does not have any internal storage, so it needs to be upgraded.
There are two ways to install this memory; with a microSD card or a USB stick. However, one should not use the cheap consumer-storage. A low-price sd flash memory, which is primarily for reading only. It is optimize for usage in a smartphone or as mobile storage. For such a flash memory, writing accesses for such a large amount of data can be excruciatingly slow.
Apart from this, such types of flash memory are limited. Depending upon the technology of storage, blocks can allow a maximum of 1,000 to 1,000,000 of erasing and write cycles (P/E cycles) approximately. (Source Wikipedia).Expensive models differ from the cheaper sd cards in the number of these cycles.
In network based Digital Signage project, a lot of daily content changes and log statistics occur. Hence, you can reach this limit quickly in cheaper consumer-storage.
In principle, since eMMC memory blocks have the same technology, they also have the issue of limited erase/write cycles. However, hardware manufacturers are aware of this issue and hence usually incorporate chips of higher quality. However, a user underestimates the risk of low-priced product and takes advantage of the seemingly favorable cheaper variant for his raspberry pi.
In 2012, I supervised a project in which the same thing happened due to cost reasons. The service installed consumer USB storage into the media player. These USB storage were not even the cheapest available. Nevertheless, in less than a year, the devices failed and screen became black. In all cases, a technician service was called to replace the USB stick with a higher quality model. This exceeded the actual price by multiple times.
You don’t want such a thing to happen in your Digital Signage project.
You can avoid such a mishap by using an industrial memory in case of Digital Signage and Raspberry Pi. SLC components are one of the highest quality components. You can also use a cheaper industrial MLC flash of a higher capacity, which will allow the erase/write cycles to be evenly distributed. But, it comes with a price:
For industrial usage, MicroSD cards with SLC memory. For example, on ATP, the cost of 8GB capacity is about 93 EUR (as of January 2018) Source ATP
Industrial MicroSD cards having 8GB of cheaper MLC memory, depending upon the order amount the cost caries between 30-40 EUR Source for Panasonic
We would need a higher capacity to use MLC memory, 16 GB being the least recommended. So, at the end of the day you’d be paying approximately the same cost as that of SLC memory.
The cost aspect of thigh quality USB memory is quite comparable. There are two disadvantages also; a stick requires more power than a microSD card. The Raspberry Pi, having a standard power supply of 2.5 amperes only, could get overwhelme with that. Furthermore, a USB stick extrudes out of the device, requiring space which may not be available.
In addition, this represents a mechanical source of error that must be secured in signage projects. Someone could come up against it or remove the stick maliciously.
Raspberry Pi 3 Starter Kit with power supply and housing: approximately 60 EUR (Source Amazon)
8 GB SLC MicroSD: 93 EUR (Quelle DigiKey)
The pure hardware costs of operating Digital Signage with Raspberry Pi securely in a network are approximately 153 EUR! (As of January 2018)
We can get much more powerful and 4K-capable digital signage hardware of at least 8GB eMMC memory or higher in less than 100 EUR.
A Raspberry Pi Compute-Module 3 with a 4GB eMMC memory is currently available for 30 EUR (Quelle Raspishop – As of January 2018). However, this module doesn’t come with a WLAN chip, and 4GB memory is only suitable for SD videos and short HD playlists.
In October 2020, the Raspberry Pi Foundation released the CM4. This also has two HDMI outputs, up to 8GB of RAM and, like the CM3+ presented in January 2019, it can drive up to 32GB of flash memory. This should make space worries for HD or 4K content a thing of the past. Furthermore, the CM4 even has a PCIe 2.0 interface. It can do Bluetooth, but still no WiFi. The price ranges between 25 and 90 EUR.
Furthermore, you need a carrier board if there’s no slot with the I/O interfaces. This again costs you around 100-110 EUR. Only a few NEC monitors have an onboard Computer Module.
This means that the cost reaches to at least 130-140 EUR, which unfortunately makes it unappealing.
In principle, I think using a Raspberry Pi in digital signage projects is a mistake. As much as I'm impressed by the hardware of version 4 and its price, I wouldn't advise anyone in good conscience to run networks with it.
In my opinion, if content change and playback statistics are no longer require then you can use Digital Signage and Raspberry Pi. For instance, to run an endless loop of tool demonstration in a hardware shop or play an image video for kitchen equipment in furniture shop.
Though, for that one could also use a 5 EUR Raspberry Zero, without WiFi.
However, the situation would change if the content is regularly exchange on a weekly or daily basis and the customer requests the playback statistics. So, you need to upgrade Raspberry Pi cost-effectively. In short, it’s not worth it, and one should consider other alternatives.
In some cases, the Compute Module 3, 3+ or 4 may be of some help. For instance, if like in NEC monitors the slots already exist, the content in case of CM3 doesn’t require much memory, and you do not need integrated WIFI.
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