The Portsdown 4 - Hardware Standard

Discussion about this major DATV Project. See also https://wiki.batc.org.uk/The_Portsdown_Transmitter
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G8GKQ
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The Portsdown 4 - Hardware Standard

Post by G8GKQ » Sat Jun 27, 2020 9:15 pm

I announced the forthcoming Portsdown 4 in CQ-TV 268, issued today.

The Portsdown 4 will be based on the Raspberry Pi 4, and I have been asked which model of RPi 4: the 1 GB, 2 GB, 4 GB or 8 GB? The reason that it wasn't stated in the article is that I don't know yet.

I am doing all my initial testing using the 2 GB model, and I think that will be sufficient - but I haven't finished all the testing yet! I certainly would not advise buying the 1 GB model (if they are still available).

Dave, G8GKQ

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Re: The Portsdown 4 - Hardware Standard

Post by G8GKQ » Mon Jun 29, 2020 9:44 pm

I have been asked whether the Rpi 4 will give any immediate advantages over the RPi 3:

The RPi 4 will be allow me to do things that the RPi 3 couldn’t because it ran out of processing power. One immediate example is that when trying to play the video input from an EasyCap (ie using the Portsdown as a monitor for local composite video or received 5.6 GHz FM), I can run it fullscreen with audio. It copes with the processing required to scale the video to 800x480. The old RPi 3 didn’t and I had to do the simple /2 scaling to 360x288 which gave a small image in the middle of the screen.

The second less obvious advantage is that it enables me to do a reset on the complete hardware specification and cease support for some legacy devices and possibly unused capabilities in the Portsdown 4 build. The first example of this is not supporting the BATC Filter Modulator Board. This reduces my workload for testing enormously! If members want to use these old capabilities, they can still buy an RPi 3 and run the old software - so nobody is disadvantaged.

Dave

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Re: The Portsdown 4 - Hardware Standard

Post by g0mjw » Mon Jun 29, 2020 10:00 pm

Hi Dave

Great progress so far. Can we standardise on GPIO use? You already know about the relay boards. I am not sure there is anything else yet apart from perhaps support for IR remotes and perhaps a rotary encoder, though we have been using mice for that. Also audio - it's mono or stereo?

Mike

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Re: The Portsdown 4 - Hardware Standard

Post by G8GKQ » Tue Jun 30, 2020 8:59 am

Hi Mike

GPIO usage will be evolved from the current Portsdown Classic standard defined here https://wiki.batc.org.uk/PTT_and_band_s ... onnections, but with modifications to enable full Langstone compatibility. I will publish the new pin allocation on the Wiki when the initial design is finalised.

The use of a GPIO-connected rotary encoder is not envisaged because it would require major software changes, and the current USB-connected mouse electronics based solution works really well. The use of IR remotes for the Portsdown is not planned; that is a Ryde capability.

Audio output is always stereo; audio input is mono if coming from the USB audio dongle, but stereo if coming from an EasyCap or C920. Transmitted audio has 0 or 2 (possibly identical) channels. Received audio is played as stereo.

Dave

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Re: The Portsdown 4 - Hardware Standard

Post by g0mjw » Tue Jun 30, 2020 11:08 am

Hi Dave

Thanks. Stereo for me is only an issue as I only fitted one speaker, which is currently on the left channel. I will modify to combine both. Should be just a matter of connecting left and right together. My audio amplifier came from EBAY. It is class D, runs off 5V and is great incidentally. Is there any point in bringing out one of the HDMI ports from the case?

Mike

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