Saturday, 24 August 2013

Latest screenshot of Express

Here is the latest screen shot of the host software. I have made some minor
changes including a transmit delay, which shows the time delay from the video
capture to actual transmission.

I am now working on making the software more robust and tiding it up
internally. I have working versions for 32 and 64 bit Ubuntu. Also I am
trying to remove all the machine dependencies so that it should be able
to compile on a MAC. I don't intend producing a MAC version but I have
been made aware that someone wants to try doing that.  

I found an issue with USB VBUS handling which meant if you pulled the
USB cable out the board went into suspended mode and did not recover
when the cable was plugged back in. I also was not allowing enough time
after an FPGA reset before I started to try to load the FPGA configuration.
That now should perform correctly.

One outstanding problem is that libusb can be very delicate as can the V4L
stuff. there is not much I can do about that other than follow the programmer's
guides to the letter and hope.


  1. Regarding frequency stability (I apologize if you mentioned this already): I have the feeling that frequency stability must be made pretty good. Is there a spec on how good this must be? Very interesting project, and fun to read about your developments!

  2. DVB-S being consumer equipment has a fairly wide locking/tracking range. The Xtal oscillator module the board seems stable enough.
    DVB-S/S2 receivers just use cheap references.
    If people want very precise frequency control the board could be
    GPS locked. The oscillator would need removing and a slight change
    made to the Host program (to tell the PLL it now had a 10 MHz reference rather than the 20 Mhz one it comes fitted with). Also you would have to connect up your GPS source of course.

    1. Thanks! I was looking for GPSDO prices, but they all say: write for a quote, which usually means all my spare change, ha.

      The next idea, was to steal someone else's GPSDO signal, like my local US TV station HDTV pilot. Of course I have no experience in that.

      Does the onboard 20 MHz xtal drift around pretty slow (after warmup)? Also, is this a 1 ppm part, or better than that?

      Just curious technically!

  3. It is an ASE 20.000MHZ-LC from Abracon which is a 50 PPM part.
    I have not measured the drift but it is more than adequate for
    our requirements.

    1. That's great, as I had a misconception for the stability required.