Portsdown Power Supplies

Discussion about this major DATV Project. See also https://wiki.batc.org.uk/The_Portsdown_Transmitter
M0YDH
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Re: Portsdown Power Supplies

Post by M0YDH » Sun Feb 10, 2019 12:04 am

Hello Dave

My 2019 build today had a dodgy micro USB connector to wiring stub so I connected the Pi to the powered USB hub and the 3A buck converter [3 pots and a red board type] set at 5.3V (no load) did really well. Lime and all accessories were there too. No low voltage alerts after two transmit cycles. Is that an acceptable way to go?

My RPi model 1 was powered off a USB hub which lives in my Portsdown accessory box today. It was the recommended thing to do in the Beginning of Pi.

I saw this short connector https://thepihut.com/products/short-mic ... pi-display which would suit as the Pi sits over the hub in order to get a smaller package size.

regards

David

radiogareth
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Re: Portsdown Power Supplies

Post by radiogareth » Sun Feb 10, 2019 9:03 am

In pursuit of minimal voltage drop and to rule out any PSU induced noise, I found the relevant RPi circuit (3B & 3B+ are different IIRC) and soldered wires direct to the RPi circuit board. I used a LM338 adjustable regulator (up to 5 amps subject to dissipation) set to 5.2 volts and fed through a TO220 diode for reverse polarity protection. Tested on my heatsink with 1.2 amps load at Vin 13.8 (worst case) and it was stable at around 50C. Actual load is about half that, usually with a lower overhead too as I use 3-Cell Li-ion laptop packs as portable power.
Gareth

M0YDH
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Re: Portsdown Power Supplies

Post by M0YDH » Sun Feb 10, 2019 12:24 pm

Good point Gareth. The 3B+ circuit schematic sheet 1 shows PP2 on the supply line after the connector and before the fuse.
Ground connection PP5 is too close to PP2. PP3 is easier to access. My Pi 3B+ powered up fine with 5.2V across PP2 & PP3. So careful wire soldering is on.
Cheers
David M0YDH
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PhotoPictureResizer_190210_122355378-1008x756.jpg
Pi 3B+ power points.
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keng8vdp
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Re: Portsdown Power Supplies

Post by keng8vdp » Sun Feb 10, 2019 1:02 pm

M0YDH wrote:
Sat Feb 09, 2019 11:47 pm
Hello Ken
I've been in your shoes with Portsdown.
Many of us have bought 2 Waveshare screens. The safest bet is to get it cased up in a printed plastic surround [e.g. from radiogareth] ASAP and use a ribbon cable connector.

Colin G4KLB's Portsdown was very influential and I copied it too. It's a great piece of work and won a prize at CAT17 IIRC. Colin has a big shack with lots of desk space so can plug USB items in to the Pi without mounting them in the case. The connections on the side of the case have become a nuisance for me in my rack system. A lot of the precious space on the rear panel is taken up with buck converters. So later features like composite video/audio out and e.g. signal generator port don't feature. The band select board shown has no outputs. My first Portsdown has an accessory box for the powered USB hub to house the gear that didn't fit in. There's a further unit to do Rx/Tx changeover and amp selection.

You've found the interconnect diagram. :D I found it baffling at first! I looked at it today and its seems quite elegant. (Portsdown 2019 thatI put together today only uses 3 main groups from the breakout board - 2 if no attenuator - you're doing the full fat version ;)

The Pi needs a net 5.1 V across it from its own regulator - you are correct. A buck converter or LM338T home brew per the Texas Instruments data sheet do well. A small LCD voltmeter is handy as part of the set up so you can tweak it. Ripple filters can be added - my arrangements came from LM2756 data sheet. G4KLB's has these after each buck converter.
The ADF4351 uses one of the buck converters as it seems to need 6-8 VDC - see Wiki. I've soldered a wire to the back of the power connector housing. Only LE, CLK, DAT and GND come from the Portsdown.
I have a 7805 regulator for the LO filter (and I think FM board too) 5V. It could take supply from the same regulator as the Pi.
The 3.3V line from the breakout board does 4-Band decode and the RF switch.
The FM board is supplied from 12-13.8V supply and has on board voltage regulation. In any event do what G8GKQ says!

A Stripmaster and a crimp tool for Molex KK connectors will help enormously.
I hope this helps.
David M0YDH


David ,
Thanks for that info. very useful. By the way my touch screen got damaged whilst i was messing with a screen ribbon extender. A frend made me a bezel on his 3d printer. I also have the molex connectors all wired but was waiting for the dupont type Plug which came yesteday for the ADF435x . Fiddly things but that end of the 4 wires LE, CLK, DAT and GND is now done too.
Like you I have this morning soldered wires direct to underside of the power socket. I do have a plug with cable for it but silly me mounted the ADF board too close to the BUCKS to get the plug in !
Of all things im building into a Ferrero Rocher see through plastic box ( I ate only the last one and "she" ate the rest ). I only bought them for her at Cristmas so I could have the box !
Yes I have printed out that wiring layout / interconnect and yes I agree its quite neat.
Its the test bed and if it all works I have a very nice metal case I will build into that matches my 2 lots of Analogue gear 1 for 23cm and one for 13cm.
I dont have ALL the boards YET but ive all the bits for the 23cm 1st test.
So, Once ive connected up the 3 bucks ( after setting the voltages ) it will be test time.
The ribbon cable ( from piHUT for the screen doesnt fit nice on the pins on GPIO board and the plastic shell is too wide at the ends) I'm intending to cut off the not used pins on GPIO as the cable should fit better. It was when fiddling with this ribbon that I duffed the touch screen. However its only the touch part that gone AWOL. the actual display is fine.
Im just about to check / determine the pinouts on USB PLUG so I can use a cut off USB lead for connecting the PI to one of the Bucks. If I remember from my time replacing USB sockets on TomTom sat/navs I do already know BUT i need to be sure of course.

Once again thanks for your help. Ken G8VDP

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keng8vdp
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Re: Portsdown Power Supplies

Post by keng8vdp » Mon Feb 11, 2019 10:59 pm

I've powered everything and its working. I scanned on a satlink and I see the signal OK spot on frequency on its display, and on my ICOM 23cm mutimode. I also see it on my frequency counter. The satlink has a good signal strength of 75% or stronger. It finds and displays the frequency and the symbol rate on a blind scan. The LOCK LIGHT lights and stays lit. Ive done a PID scan too and it finds the signal and displays some parameters and tje lock light locks on. The problem is I get no picture using either the Portsdown testcard or my testcard via easycap. I can see both on the pi screen in capture mode. I've set video source, symbol rate, frequency , output etc but no image is seen on sat RX. 5 hours of trying different things and settings and no luck. For the moment I'm puzzled. I need a headache tablet, a cup of tea and a lay down.

This post is now , perhaps on wrong thread but I thought I'd put it here just to let you know your help above has got me to this point.

Thanks all Ken

G8GKQ
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Re: Portsdown Power Supplies

Post by G8GKQ » Mon Feb 11, 2019 11:10 pm

Hi Ken

Make sure that you have Encoder: MPEG-2 selected. If it is finding the PID, it seems that the SatLink simply can't decode the video.

Dave

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keng8vdp
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Re: Portsdown Power Supplies

Post by keng8vdp » Tue Feb 12, 2019 6:56 am

G8GKQ wrote:
Mon Feb 11, 2019 11:10 pm
Hi Ken

Make sure that you have Encoder: MPEG-2 selected. If it is finding the PID, it seems that the SatLink simply can't decode the video.

Dave
Dave
I "think" I've tried that but I'll try it again.

I have several satellite receivers Comag etc + a posh rack mount one. I've yet to try those.

First time I tried the Satlink was on GB3YT it took a while to get it to see it. Having gone within 500 yards of it.
Next time was on Anglesey but by then I'd learnt how to drive it. Or just got lucky !

Also my very good friend Gary M1EGI has a MiniTiouner that he can bring down. He's not old like me , he's young & keen.
I must admit, my brain still works in analogue and I'm very slow to understand FEC Bouquets PIDs etc.

I also got confused when the filter modulator board got mentioned further up this thread calling it the FM board in an earlier reply . then found out it wasn't (the FM as in SSB AM FM ) but it meant
"filter modulator". Duh !

Many thanks Ken

This is screenshot of video I took yesterday. Don't try tapping the triangle :D
IMG_20190212_073658_434.jpg
See Mpeg 2 is set
IMG_20190212_073658_434.jpg (107.4 KiB) Viewed 379 times

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keng8vdp
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Re: Portsdown Power Supplies

Post by keng8vdp » Tue Feb 12, 2019 12:37 pm

Messing & messing and more messing ..then Bingo
IMG_20190212_123550_545.jpg
IMG_20190212_123550_545.jpg (123.83 KiB) Viewed 350 times

M0YDH
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Re: Portsdown Power Supplies

Post by M0YDH » Fri Mar 08, 2019 6:51 pm

I'm able to run all 5.2V services in the Portsdown 2019 off this buck converter from Ebay
https://www.ebay.co.uk/itm/DC-DC-CC-CV- ... 2749.l2649

It is described as DC-DC CC CV Buck Converter Step-Down Power Module 7-32V To 0.8-28V 12A 300W. It has a two colour LED where blue is no load. It runs the Lime Mini, USB Hub, all USB accessories, Pi and 3.5" screen with the blue light on then blips to it red loaded LED when a command or transmit is pressed. I haven't added the 1 amp C920 web cam yet.

It runs cool and seems to be the solution to power distribution. Does anyone foresee a problem with this ? Or have any experiences of these converters in term of excessive noise?

I have a voltmeter across it which is very good. Ebay again and described as 3 Wire 0.28" DC 0-100V Voltmeter LED Panel Digital Display Voltage Meter Car LCD

Cheers

David M0YDH

G8GKQ
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Re: Portsdown Power Supplies

Post by G8GKQ » Sat Mar 09, 2019 11:01 pm

David

The only problem with that buck converter is that it does current sensing in the the negative (ground?) circuit. So your outgoing negative supply is not going to be at the same potential as your incoming negative supply. This can be an issue as most of us just use the chassis as ground - both before and after the power supply.

I use lower current (5 amp) buck converters in 3 of my Portsdowns which have this arrangement. However, I have shorted across the current sensing resistor, which gets rid of the problem, but also removes any short-circuit protection or current limiting. Increases the risk of power supply failure, but makes it work. I'm not sure that I would recommend this with a 12 amp device.

Sorry - not the answer that you wanted, but if it is working for you I would stick with it.

Dave

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