Portsdown boxing/build thread

Discussion about this major DATV Project. See also https://wiki.batc.tv/The_Portsdown_Transmitter
M5TXJ
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Re: Portsdown boxing/build thread

Post by M5TXJ » Mon Oct 29, 2018 8:37 pm

2 spare USB sockets? Pi has 4;
Easy-cap, USB Sound dongle and RTL use 3 surely...
73 Dave.

radiogareth
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Re: Portsdown boxing/build thread

Post by radiogareth » Tue Oct 30, 2018 2:52 pm

Not bothering with a sound dongle, I'll use the easycap audio in (I think I've read that works) or my C920 = 2 :-)
Gareth

radiogareth
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Re: Portsdown boxing/build thread

Post by radiogareth » Wed Oct 31, 2018 7:05 pm

In an attempt at doing a 'nice tidy front panel' I'm assuming there is little point in using BOTH audio inputs to the easycap dongle? Or is it worth keeping both? for e.g. a camera with built-in audio and e.g. a separate roving mic? Equally I'm not sure its worth providing the S video socket with panel space. But at this early stage I'm happy to listen to all reasons for and against. Its already got a RPi camera on HDMI cable and a socket for my Logitech C920. As I already have the Easycap and as there is plenty of room in the case its staying 'just in case'.

Thoughts please :-)

Gareth

G8GKQ
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Re: Portsdown boxing/build thread

Post by G8GKQ » Wed Oct 31, 2018 9:13 pm

Hi Gareth

If you only use one audio input on the EasyCap, your audio will only come out of one of the receiving station's stereo speakers. So I would suggest bringing them both out, or paralleling them inside the unit and having a single socket driving both.

S-video is probably not worth it unless you have an S-video source. I don't, so none of mine make it to the panel.

Dave

radiogareth
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Re: Portsdown boxing/build thread

Post by radiogareth » Thu Nov 01, 2018 9:04 am

Thanks Dave, I presume joining L&R via a 1K resistor each would work for the parallelling of audio ins? I think the only SVideo I have is a Hi8 video camera from a very long time ago. Plenty of other sources now.
Gareth

radiogareth
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Re: Portsdown boxing/build thread

Post by radiogareth » Thu Nov 01, 2018 2:12 pm

Moving things on, I have a choice to make:
I've bought some LM338T (data here http://www.ti.com/lit/ds/symlink/lm338.pdf ) offering quite a step up in performance compared to 7805's (5 amps peak subject to overhead and current draw). The IO filter modulator already has its own (linear reg) 5 volt supply and I'm going to hard-wire my RPi3B+ as per the RPi foundations documentation +ve to PP2 and Ground to PP5 (actually 3-6). This negates to loss through the micro-USB but retains the protection the RPi was built with. I'm going to adjust the LM to give 5.2 Volts and mount it on the back panel.

OR.....
2018-11-01 12.23.11.jpg
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Alternatively, I've hacked one of these nice little SMPSU modules (original in the background) to raise the display height above components to allow for front panel mounting, allow on-the -fly adjustment without messing about removing it from the front panel and added the suggested L&C filter components to the output, finally re-soldering the output connector block. The benefit of this is the display can show V in or V out, or for miserly portable operation, display off via two push-buttons.

I like the display option, but the purist says use a linear regulator. Does it matter for the RPi and DDS/switching boards? From what I've read, no.

Thoughts....

Thanks

Gareth

g0mjw
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Re: Portsdown boxing/build thread

Post by g0mjw » Thu Nov 01, 2018 2:31 pm

radiogareth wrote:
Thu Nov 01, 2018 2:12 pm

I like the display option, but the purist says use a linear regulator. Does it matter for the RPi and DDS/switching boards? From what I've read, no.

Thoughts....

Thanks

Gareth
I don't think any noise side-bands will be a problem, I live miles away.

Linear regulators are not great at removing high frequency ripple. You might want to put an RC filter in there before the LO regulator if you have the voltage headroom.

Mike

radiogareth
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Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Thu Nov 01, 2018 5:46 pm

Now looking at audio out for the RTL dongle and streaming. This thread https://www.instructables.com/id/Raspbe ... -Easy-RCA/ looks good for connecting to the RPi audio (no audio dongle used), via a couple of Resistors (1K) and thence off to a nice little amp board I found on eBay. https://www.ebay.co.uk/itm/PAM8302-2-5W ... 2749.l2649
Got some nice mylar cone headphone speakers to try for suitable audio (when mounted in a cavity) or somewhere I have some mylar cone 4 ohms jobs.
Work in progress....
Gareth

g8vpg
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Joined: Fri Oct 11, 2013 9:35 am

Re: Portsdown boxing/build thread

Post by g8vpg » Thu Nov 01, 2018 6:23 pm

I've had a lot of trouble with these Ebay sourced switch mode step up/down boards. Its not what they do to the device they are supplying, but the wide band RF noise they produce that makes 2m talkback impossible to use for all but very strong, local signals. I've had to replace them all with alternatives and so I would recommend avoiding them.
73 Shaun.

radiogareth
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Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Wed Nov 07, 2018 9:25 am

Anything else I should/could put on the front panel? Before I commit to aluminium....
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L to R Main power and indicator, RPi touchscreen and integrated pen holder, voltmeter module for Vin (battery when portable) and VRPi to check, centre off switch below to select display or off. Video and audio in for videocap, then 5 LEDs for band and tx indicators. Seems a shame to leave space ;-)
ABout the only extras I can think of ATM would be remote RPI power and activity leds, duplicates/replacements of those on the RPi PCB.
Gareth

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