What is DigiThin?

The place for discussion about the RPi add-on RB-TV modulator card developed by G4EWJ and supported by the BATC Shop
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G4EWJ
Posts: 640
Joined: Wed Feb 17, 2010 10:11 am

What is DigiThin?

Post by G4EWJ » Mon May 11, 2015 3:59 pm

DigiThin is a narrowband QPSK modulator pcb, which sits on the Raspberry Pi model B 26 pin header. Symbol rates of up to 333k are possible. Bandwidth is roughly 1.5 x symbol rate. RF output is 1mW.

Software by F5OEO running on the RPi takes MPEG-4 video from the RPi camera, converts the data to IQ format and sends it to the DigiThin pcb. An external local oscillator sets the transmit frequency. The modulator chip specification is 100-1000MHz, although G4KLB has had it working on 50MHz and 70MHz.

It can be received using the Tutioune software from F6DZP, with a suitable receiver. Most set top box receivers do not handle such low symbol rates, so a satellite receiver module or a PC satellite receiver card is required.

It is designed for home construction, with no difficult soldering. The chips are SOIC with 1.27mm pin spacing and the other SMD components are at least 1206 size.

It is an experimental project, rather than a finished product and there may well be circuit modifications required as more people build it. The software is likely to change, so a dsPIC33F programmer is necessary.

Partial kits are now in the BATC shop.

For more details, see the article in this BATC magazine: http://www.batc.org.uk/club_stuff/rbtv.pdf

Brian
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g0mjw
Posts: 479
Joined: Sat Sep 20, 2014 9:15 am

Re: What is DigiThin?

Post by g0mjw » Wed Apr 25, 2018 3:45 pm

My original PI based digithin DATV transmitter is still working and a useful test source. Is there any updated software? For example to allow it to display a test card instead of the camera? It's not a Portsdown and it has no screen or display but there has been quite a lot of software development since it was developed. Can it (simply) run Portsdown?

Mike

G4EWJ
Posts: 640
Joined: Wed Feb 17, 2010 10:11 am

Re: What is DigiThin?

Post by G4EWJ » Wed Apr 25, 2018 10:22 pm

I use a very old version of rpidatv on mine, to transmit .ts files. I seem to remember that I tried a more up to date version, but I couldn't make it work on the original Pi B. In theory, it should. I must try again with a later version.

I haven't gone down the Portsdown route yet, so I'm not sure about the possibility of using a DigiThin.

Brian

g0mjw
Posts: 479
Joined: Sat Sep 20, 2014 9:15 am

Re: What is DigiThin?

Post by g0mjw » Thu Apr 26, 2018 4:49 am

Mine is using a later PI B after the original stopped working, so I suppose it might have the MIPS.

Mike

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