New Raspberry Pi 4B up and running!

For about two years now, I've been running a Raspberry Pi 3B+ as my portable/mobile computer for digital operations. In all that time, in all that banging around and being cooked, then frozen inside a car every day, the Pi has never failed.

Fairly slow, but painless test installation of the new Pi 4B, already running WSPR.

With this success in the background, I thought I'd try a Pi 4B, with 4GB RAM.  One thing I expected would make the 4B less attractive than the 3B+, itself a very capable and fast machine, is the added power consumption, fed by a lot of anxious online talk - as there also was when the 3B+ came out - about CPU heat.  I elected to fit a passive aluminium heatsink case because of this, instead of a standard plastic or metal case.  I used heat transfer compound to make contact with the chips, rather than the supplied pads.

It turns out, though, that at a fairly typical resorce load, the 4B only uses about 6% more power than the 3B+.  With all the cores pushed to the limit, the difference increases to 31%.  But use of WSJT-X is fairly undemanding, and so we can assume something like the lower limit for this application.  The heatsink proves to be only hand warm when running WSJT-X - nothing to worry about there.

What does this mean in practice?  Well, I can run the 3B+ plus its 7" Waveshare screen for at least 5 hours, and probably much longer from a small ~20Ah Li USB battery pack.  So the 4B should not suddenly see usable times come down dramatically.

Pi 4B decoding nicely!  Waveshare 7" LED touchscreen (with my own timber frame, to attach to a 'go-box' lid later on)

The real question is: do you need a 4B and its slightly higher power use for field digital operations?

My view is: no, you don't, even though the two versions cost much the same.  The 3B+ is perfectly good enough for all digital modes and has, I think, the perfect balance between performance and power use.

I can't see anything other than a marginal increase in decode speed of weak WSPR signals with the 4B.  The 3B+ has also proved itself over and over again, although there's no reason to doubt this won't also be true of the 4B.

UPDATE: I ran the Pi 4B for 4 hours and 10 minutes later in the day.  At this stage, the USB battery was still only half empty, although it may be that non-linearity in discharge means we can only expect maybe another 60-90 minutes of further reliable operation.

So, roughly 5-6 hours' operation from a hand-sized power pack, with plenty of waking the screen up during this period, is a very good result and indeed much the same as that seen with the Pi 3B+.

Accurate temperature measurement with a DMM probe inserted into the heatsink fins.

Decoding speed is a couple of seconds faster than my HP laptop with decoding set to 'deep' on both systems.

Interestingly, the Pi 4B doesn't seem to produce the RFI that is often seen with a 3B+, which can be quite strong, even when housed in a metal casing.  This strongly tips things in favour of the 4B for radio work. 

Despite having all that aluminium in intimate contact with the board, wifi connection reliability remains excellent.  Similarly, the Bluetooth connection outdoors is good out to around 15-20 metres in the clear.

Temperature measurements with a multimeter probe inserted deep into the aluminium heatsink gave 37 degrees Celsius after an hour of operation (ambient = 18.5 degrees C), confirming the low resource demand of WSJT-X.

Anyway, I've a fairly exhaustive page on setting up the Waveshare screen and some advice on WSJT-X set up here.

WaveShare 7" LCD Screen

Yesterday, I received my new, small screen for the Raspberry Pi.

I bought this so that my power consumption for a solar/battery shack is cut by 60% (to about 5W) from that of using a full sized screen (around 12W).  More importantly for radio, it also gets rid of the very RFI-noisy large monitor, restoring peace to the HF bands.  The extra space freed-up by the diminutive screen is also very welcome.

The screen is a 1024 x 600 WaveShare 7" (17.8cm) LCD, which I bought for £60 from ModMyPi.  It has a HDMI input, and touchscreen capability. 

Success, but it took me a while to get there!  The very high display quality is not really evident in this photo.

The screen comes complete, but you have to assemble the plastic enclosure, which is machined to a very high standard.  Fitting the whole thing together is quite fiddly, but simple.  You can save a fair bit of money if you buy the screen without a frame.  For radio purposes, the lack of plastic frame often makes mounting the screen easier.

There are no instructions with the screen, which is strange, because it doesn't need a lot of instructions; just a few lines are enough.

Instead, you have to visit a Wiki page for the device.  This is fine, but a little 'Chinglish' in its delivery. 

What is not clear, until you spend hours playing around with the Raspberry Pi's config.txt file, is that the configuration changes simply need to be added at the end of the config.txt file.  You don't edit those values already in the file, which is how I thought it worked.  I think the maker and/or the seller should stick a simple few lines of advice on this in the box.  But margins are so low they don't bother.

For posterity, and to help those struggling as I did, what you have to do is:

(1) Connect your Pi to a normal-sized HDMI screen such as a TV, PC monitor, or recycled laptop screen (the latter idea, with a suitable screen driver from ebay, is a good, though more cumbersome (and non-touchcreen) alternative to the Waveshare, and a little cheaper, that also does not need any of these config file modifications)

(2) Boot up your Pi.  With normal-sized screens, it detects the correct display setttings without user input.  The Raspberry Pi 4B may settle down into correct screen display without these settings, but it might prove unstable; you are much better to change the settings as given.

(3) Click on the command dialog box

(4) Type in sudo nano /boot/config.txt  (note, there must be a space between 'nano' and /boot). 

(5) Immediately below the last command that is already in the config.txt file, (i.e. do not insert spaces or blank lines, but immediately below), enter the lines below accurately:

max_usb_current=1
hdmi_group=2
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0
hdmi_drive=1

There must be no spaces before or after the '=' sign, and the numbers in the hdmi_cvt line have a space between the 'cvt' and 1024, and then spaces between each number (i.e. hdmi_cvt<space>1024<space>600<space>60<space>6<space>0<space>0<space>0)

If you use the LCD with Raspberry Pi 4 B, you need to remove the line 
dtoverlay=vc4-fkms-V3D from config.txt file

(6) Press CTRL X and press 'Y' for yes to save.

(7) type sudo reboot and press <return>  It may be better to disconnect the Pi from the large display and reconnect it to the Waveshare before pressing <return> 'blind' (without a screen to see proceedings).

(2019 December 23 - REMINDER TO ME: Audio input and output in the WSJT-X software settings should be sysdefault:codec; also on new Pi installs, make sure audio input/output is USB Codec).

One reason for making the instructions clearer is that if you get it wrong, you will have to go and edit the config file on another computer (if you can access the config file, which isn't always the case). If you can't see it on a PC, for example, the fastest turnaround is to quick-format the SD card again on a PC and reinstall the NOOBS files, then insert into the Pi for it to reinstall its OS, then go to the top of the instructions above at number (1).

Once I understood and wrote these lines into the config file, the screen immediately went from being a mess of flashing lines to a full-colour, vibrant display.  Power from a USB 'powerbank' is enough to keep both the Pi and the screen running for several hours, making backpacking a reality.

Other people have commented that this screen has a high quality display, and indeed it does!  Instead of a low resolution display like you get with so many other models, this is just like using a full-sized monitor in miniature.  It isn't a struggle to read the screen at all.

The screen has attachments for the Pi itself on the back, which then effectively gives you a Pi-based tablet, or a small laptop, with the considerable advantage of being modifiable for many practical projects.

One piece of advice for Raspberry Pi 4B applications: the screen comes with a micro-HDMI male to female adapter, which is very bulky and doesn't make for a very robust connection.  I strongly advise you to buy a micro-HDMI male to full size HDMI male cable, which is far more secure and much less heavy on the Pi's HDMI board socket. 

A great product, provided it stands the test of time! UPDATE: I've been using this screen for 4 years now, and it's seen some tough action: left in my /A site for months, which is cold and damp, and also a lot of roughing it in my car with /P seaside operations.  This is a good product!