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Raspberry Pi stays cool: Tips for cooling the mini PC


Since the first model in 2012, the Raspberry Pi has seen an enormous increase in performance compared to the current Raspberry Pi 4 B. The new boards require adequate cooling. The article shows solutions using hardware and software.

With higher power and higher clock frequency, there is a higher heat emission. The first

Raspberry Pi
With an ARM processor core and a maximum clock frequency of 700 MHz, the surface of the chip alone was sufficient to remain at reasonable temperatures. For models 2 and 3 and overclocked circuit boards, glued-on heatsinks were sufficient. With the Raspberry Pi 4 with four cores and a clock frequency of up to 1.5 GHz, the heat development becomes a factor that must also be kept in mind during normal operation.

According to the specifications of the Raspberry Pi Foundation, the Raspberry Pi 4 should run reasonably well even without active cooling – and should not be damaged, especially when overheating from 85 ° C. The Cortex-A72 processor is therefore designed to automatically clock down when the heat is too high – from 1.5 GHz to 1.0 GHz and finally to 700 MHz. This means that the cooler the board runs, the higher the total output remains in continuous operation. It also means that it would be pointless to slow down a Raspberry Pi with undervolting and underclocking, the board does that itself.

Shopping cart iconSee the Raspberry Pi Foundation mainboard “Raspberry Pi 4 model B 4GB LPDDR4” at Otto

The Broadcom tool vcgencmd is used in the customized Raspberry Pi OS (formerly Raspbian) to display the current temperature and CPU clock frequency. The command

sudo vcgencmd measure_temp 

shows the temperature of the system and

sudo vcgencmd measure_clock arm 

outputs the current clock frequency of the ARM cores in Hertz. If you place a “watch” before each of these commands, you will receive an updated version every five seconds.

Raspberry Pi:

Lots of uses

Fresh firmware: less power consumption

The Raspberry Pi 4 came on the market with a power consumption of 7.28 watts, while the Raspberry Pi 3 (B +) consumes a maximum of 5.77 watts. In the meantime, five firmware updates have been released by the Raspberry Pi Foundation, which add stricter energy management, reduce energy consumption by 0.8 watts and thus curb heat development. The first step after commissioning a Raspberry Pi 4 should therefore always be a firmware update. The recommended way of a firmware update is a complete upgrade under the official Raspberry Pi OS system:

sudo apt-get full-upgrade

The command shows the date of the firmware used

and should display June 1, 2020 or later as the release date after the upgrade.

Passive cooling: stable lateral position

Practically as a paperweight: Passive heat sinks work via their thermal storage mass and the surface of the cooling fins.

Enlarge

Practically as a paperweight: Passive heat sinks work via their thermal storage mass and the surface of the cooling fins.

According to the Raspberry Pi Foundation, placing the Raspberry Pi 4 on the side of the pin strip also has an advantageous effect on heat dissipation. After measurements with a thermal imaging camera, this alignment best prevents heat build-up and keeps the overall temperature of the system up to two degrees lower under load. This procedure does not seem to be sufficient for continuous operation, because the Raspberry Pi 4 will still reach temperatures under high load, which will cause the CPU to slow down. The side position can therefore only help as a temporary solution if no other cooling methods are available.

Quiet accessories: regulated fans

A little cool breeze: The rather small fan shim from Pimoroni is sufficient to cool the CPU and has control electronics that regulate the fan motor using a system process.

Enlarge

A little cool breeze: The rather small fan shim from Pimoroni is sufficient to cool the CPU and has control electronics that regulate the fan motor using a system process.

© Pimoroni

One of the great advantages of the Raspberry Pi and other boards has always been their silent operation without a fan. The usual fans of actively cooled housings are simply plugged into the GIO pins and then run at constant speed. There is a better solution: The fan shim of the Pimoroni DIY outfitters comes with control electronics on a mini board that is attached via the GIO pins. The speed control then takes over under Raspberry Pi OS a Python control program, which switches the fan on from 65 ° C on and off again. The Pimoroni fan is in mail order

available
. The remarkable thing about this solution is that all GIO pins remain accessible and the fan is not in the way of other attachments.

Raspberry Pi 4:

An overview of the new features

Passive coolers are more expensive than actively ventilated housings, but are also acceptable when installed correctly with thermal paste. These solutions are silent, one disadvantage is the dependence of the cooling capacity on the ambient temperature. Passive cooling plates are sufficient on the desk, but in a warm server cabinet or in the drawer, such cooling is usually not enough to prevent the Raspberry Pi 4 from overclocking. Since the aluminum cooling fins are sometimes quite massive, access to the pin strip is also blocked or requires an additional riser header as a pin extension. The passive heat sink from Geeekpi is

for around 15 euros
just like the competitor product

by Pimoroni
.

It is important for these heat sinks to do without the supplied thermal pads, because they are simply too thick. It is better, as with the assembly of CPUs, high quality and thinly applied thermal paste from the tube. This measure still makes a difference of three to five degrees.

Temperature and power: monitoring via app

The Raspberry Pi at a glance: With the Raspi Check app it is easy to control temperature and frequency over the network. The query takes place via an SSH connection.

Enlarge

The Raspberry Pi at a glance: With the Raspi Check app it is easy to control temperature and frequency over the network. The query takes place via an SSH connection.

Monitoring solutions for Linux servers are oversized in order to keep an eye on the temperature and clock frequency of a Raspberry Pi in the network. An app for Android that connects to the board via SSH also does in many cases: the Android app

Raspi check
is an uncomplicated but detailed system monitor for all Raspberry Pi models with Raspberry Pi OS as a system. In addition, the German-language app can also restart or shutdown the board via SSH. After installing the app, the menu item “Add Pi” opens the settings page for the SSH login data of the Raspberry Pi in the top right. The first requirement is obvious: The SSH server must be running on the system. The user account used must have root rights (via sudo). If a Raspberry Pi is accessible via port forwarding and dynamic domain names via the Internet from outside on port 22, then the check via app will of course also work on the go via SSH.

Stress test: high load on command

To measure the effectiveness of cooling methods, benchmarks can push the Raspberry Pi to its performance limit for a defined period of time. The tool has now become available for this

Sysbench
established, especially since it is available in the standard package sources of the Raspberry Pi OS and by means of

sudo apt-get install sysbench 

is installed briskly. The command starts a benchmark of all four cores

sysbench --num-threads=4 --test=cpu --cpu-max-prime=200000 --maxtime= 300

run for five minutes, generating 100 percent load.

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