Hardware

[g8gtz]

Hi

As Colin says the hardware design is almost finalised and tested and the performance is excellent. Big round of applause goes to Colin, John and Dave for all the work they are putting in to the project.

d.jpg (77.58 KiB) Viewed 8636 times

We're currently working out how we are going to sell it - as well as a blank PCB with component list we're looking in to whether it is practical to get some boards made up.

Watch this space.

Noel

[G8GKQ]

Sorry to keep you all waiting, but we wanted to make sure that this project has most of the bugs ironed out as early as possible. I have put the first prototype in a box, and have some facts and figures that I can publish. Here's the way that I have mounted it:

Demo Portsdown.jpg (229.73 KiB) Viewed 8626 times

The modulator board measures 95 x 79 mm and has a 5v linear regulator that needs some heatsinking. The board itself draws around 250 mA, so the regulator dissipates 2 - 3 W in normal operation. The heatsink in the picture above is not big enough for 12 V operation - I'm currently using a 9 V supply. I used a switching regulator to supply 5v for the RPi and Synthesizer, which added another 500 ma or so to the total current consumption at 12 V. I have left space in this box for an EasyCap analogue video capture dongle, a USB sound dongle and an RTL-SDR for the bonus receive capability. These will all add to the current consumption, but I do not see it getting over 1 Amp at 12 V.

Output from the modulator board depends on the band (71 - 1255 MHz), but is in the range 1 - 10 mW (0 to 10 dBm). QPSK MER measures at 31 dB on MiniTioune V0.4c. Video latency is lower than previous projects, but sound is still a work in progress for the H264 modes.

I am mounting all the connectors on the back panel, including an HDMI socket (physical standard only - they're not HDMI signals) for the RPi Camera, RPi network connection, 12 V input and RF output. I also plan to mount a USB (extension) socket, video and audio inputs and an RTL-SDR receive input. I will tidy the wiring and remove the LED indicator board when the testing and build is finalised! Note that I have left space to allow the Micro-SD card to be swapped out from the RPi (to the right of the touchscreen). The modulator board is raised from the box base to allow access to the RPi Network and USB connectors.

Great to see so much interest - it provides good motivation whilst working on the less interesting bits of the software!

Dave, G8GKQ

[G4KLB]

Well done Dave, I look forward to seeing how others fit it into a box.
The heatsinks in the parts list are designed to run on a typical portable voltage of up to 14v input but are fairly large, the one in my photo below is the small one.
There are multiple ways to fit a heatsink, there are alternative pads on the edge of the board for fitting a regulator to a chassis or laying it down flat if you don't want to use the large heatsink.
The current isn't all that large but when dropping say 9V there is a fair amount of heat to dissipate (as I say the ones in the parts list are fine).
I have used a switching power supply set 2V higher than the the regulator on all my recent projects, a small heatsink can then be used or in some cases none at all.

heat sink.jpg (311.22 KiB) Viewed 8609 times

[g0mjw]

Just for awareness really as I am sure most already know about these 7805 replacements: https://danielelectronics.com/2016/02/0 ... er-module/

If dissipation is important, the V780x(R)-1000 series are £6 from digikey - a lot more than an LM7805 but it does save a heatsink and is more efficient if you are running on batteries. A simple LC filter might help if noise is an issue. I think this route is likely to be more reliable than the ebay modules we used in the minitioune boards.

Mike

[G4KLB]

Thanks Mike,

I hadn't seen those before, could be useful for many projects.

[keng8vdp]

Great to see so much interest - it provides good motivation whilst working on the less interesting bits of the software!
Dave, G8GKQ

Wow great progress Dave, I'm getting all giddy now. We have a few interested parties here and around South Yorkshire , swapping messages and photos on our own progress getting the Raspberry Pi's , lcd's, Dongles, Easy Caps etc ready. All on Whatsapp. Some of us are a little more proficient on a PC than others and some just starting on the Pi . I'm a Pi newbie, I've eaten an Raspberry Pie before and didn't like it !
After following the Portsdown Instructions and having several problems along the way ( I don't have much hair to pull out anyway ) I have got there in the end , I think !
I have learnt a bit on the way too , which is good.
All the hard work put in already, by all those involved in the Portsdown project and also those who have gone before it even became the Portsdown, are to be commended for the superb work up to now.
I don't think you should be too concerned re the PCB / Kit/

And for Noel - G8GTZ ... having made up boards would be very very handy for some. Great idea.

Dave , Im sorry to use *"some"* of your words here but thought i would throw the ball back to you >>>
Great to see so much Progress by the team - it provides good motivation TO US whilst WE are working on the VERY interesting bits of the software ( that we could never hope to write ) and getting our heads round everything . Well done .. fear you not , we are all here willing you on.

Ken G8VDP

[M0SKM]

Hi,
This is probably a question for Colin.

Does the AD8345 run cool enough without soldering the heat transfer pad? I can do it if required but it's easier without.

Data sheet suggests it may be optional.

73 Steve

[G4KLB]

Yes, the AD8345 is fine if you don't solder the pad underneath (according to the data sheet), there are plated through holes under the pad, so its not difficult to feed some solder through those.

Don't leave the heat on too long though, or you may unsolder all the other pins, if you keep feeding solder down the holes it may slightly lift the component off the board. (Did that once on another project)

I have used it on PCBs without provision for the pad, and its never been a problem.

[M0SKM]

Finished soldering the Portsdown modulator/filter yesterday and fired it up for a first test this morning. Barring IQ balancing it works fine.

It's a birds nest of wires at the minute; but now it works I'll tidy it up.

Steve

[g8gtz]

Congratulations Steve, that must be the first one not built on the Bournemouth assembly line

Make sure it's neat and tidy as we are planning a Portsdown construction competition at CAT17 - more details in CQ-TV when we've made up the rules!

73 - Noel