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Terry Hitts EL1883 Circuit — Parallax Forums

Terry Hitts EL1883 Circuit

s2jesses2jesse Posts: 62
edited 2008-10-05 18:00 in Propeller 1
Hey guys was looking for a tiny bit of help or insight...

Ive just been getting into propellers and i coded up a nice osd with horizon and waypoint graphics etc.

I·was protoing up a little osd based on terry hitts schematic found·at the top of· his great sample spin files. I didnt quite pull it off.

I replaed the bat54s with switching diodes 1n1478's but·i dont·even know if that was the right move. Im pretty sure i got the rest of the diagram all right but just not getting a proper sync. It looks like its nearly·working but again sync seems off. I·get a bunch of white horizontal lines that look like there trying to make up the demo text.

I know this isnt much to go off but any tips from anyone who has built the simple circuit using a El1883. Im pretty new to the electronics side. Ive researched a bunch on video signals etc and get the general idea· but the tech side is still well over my head.

Thanks a ton in advance..

Jesse <--- Newb

Comments

  • BeanBean Posts: 8,129
    edited 2008-04-10 11:10
    Jesse,
    · I don't think using different diodes would matter much.

    · Does it work when not doing overlay ? (I assume you are are using the HC-OSD firmware too).

    · Do you have the filter cap and resistor on the EL1883 circuit ?

    · Do you have an oscilloscope to look at the EL1883 output ?

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Did you know that 111,111,111 multiplied by 111,111,111 equals 12345678987654321 ?

    www.iElectronicDesigns.com

    ·
  • PerryPerry Posts: 253
    edited 2008-04-10 12:23
    I have successfully duplicated Terry's overlay circuit with an LM18881 on the demo board and the proto board, using small signal silicon diodes (ie 1N4148). The bat54s has schottky diodes that have lower forward voltage. You could try germanium diodes (1N34) if you can't find schottky diodes.

    The only times I have had problems with the circuit is with certain combinations of video source and my crappy B/W TV. If the source was not quite strong enough the TV would suck down the signal so that the sync separator would not function properly.

    Perry
  • s2jesses2jesse Posts: 62
    edited 2008-04-10 17:59
    thanks for the quick responses guys...
    no·scope here [noparse]:([/noparse]
    yep got the filter caps in place
    dont think it was working without an input either fyi.

    When i get home I'll try take a screenshot of output to see if it gives a better idea of what could be wrong. ·Yep your firmware. If i dont get anything from there ill build one more circuit from scratch to check for any·errors.
    And just to double check im only using 5 pins of the el correct?


    Thanks again

    Jesse




    ·
  • MarcusGMarcusG Posts: 6
    edited 2008-04-11 16:21
    For some reason mine ONLY works if I don't have the caps... It took me forever to figure that one out, but I was having the same type of corruption, almost looked like an old monitor when the vertical sync was off. I've had it running nearly constantly for a rather long time without any problems. I apologize if it cooks anything if you try it, but this is what worked for me.

    -Marcus

    I should probably mention that what I'm using is http://forums.parallax.com/showthread.php?p=635949

    Revision 12 http://forums.parallax.com/attachment.php?attachmentid=46843

    Post Edited (MarcusG) : 4/11/2008 5:05:05 PM GMT
  • s2jesses2jesse Posts: 62
    edited 2008-04-11 22:01
    ok cool when iget a chance hopefully tonight ill rebuild the circuit from scratch and if it doesnt work ill try a temp removal of the caps..

    ·
  • MarcusGMarcusG Posts: 6
    edited 2008-04-12 04:44
    Well hopefully you don't have to resort to pulling the caps, but if you do I hope all goes well. I'm pretty sure the caps act to clean up signals, which may be why they corrupt things. Over cleaning an already clean signal. Though, I'm by no means an electrical engineer [noparse]:D[/noparse]
  • s2jesses2jesse Posts: 62
    edited 2008-04-12 21:27
    Ok fully built the circuit again. from scratch using totally differnt el1883 's. Both with and without caps as per previus posts.

    This is the 3rd time i built it very carefully [noparse]:)[/noparse]

    I·just tripple checked everything with a multimeter etc. all seems ok.

    all 3 times ive had the exact same result which is when running HITT_Video_Overlay_018 i get some white lines nearly but not quite synced up on the left of my screen.

    This is with no video input just output only.

    Im thinking the only thing it could be is the diodes however ive tried· various switching diodes the final build here is using 1n4148's·

    Here is a couple photos of the output


    vid.jpg
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2008-04-13 17:16
    Funny, if you rotate and flip the second pic, it almost looks readable.
    reversed.gif
    383 x 413 - 95K
  • s2jesses2jesse Posts: 62
    edited 2008-04-14 18:19
    Heh that is wierd [noparse]:)[/noparse]

    hrm yeah im at a tottal loss tho at what to try next.
  • Mike_GTNMike_GTN Posts: 106
    edited 2008-04-14 19:32
    Hi Jesse,

    Don't give up on this excellent design. I also built this circuit using a National Semiconductors LM1881 and IN4148 diodes as substitutes. It does work very nicely.

    Just a couple of questions that might enable you to get this project fully working: -

    1. You say your using an EL1883, did you mount this SMD part on a carrier board? or have you produced your own PCB?
    2. Could you post a picture of the setup using?
    3. No changes to the supplied Firmware? (realise your using this for the basis of your own project later on)

    I made a couple of changes to the version that I built, I made R3 680K 1% metal film, also added a 0.1uf cap in parallel to ground.
    Changed C9 to 560pf. I never touched the Chroma filter components, or had to pull capacitors out of circuit.
    Have you checked yet again that you have the correct values for R5,R6,R7 ?

    Looking on the brightside at least your getting some video generation from the project already, now is just debug time.

    Regards

    Mike.
  • PerryPerry Posts: 253
    edited 2008-04-29 15:19
    I may have discovered your problem.

    When I accidentally started the OSD module alone I got a similar display.

    Are you starting the whole application or just the video driver?

    Perry
  • s2jesses2jesse Posts: 62
    edited 2008-05-10 07:29
    ooh good question i dont have it handy at the moment
    what is·the procedure you run to get it to work.




    ·
  • PerryPerry Posts: 253
    edited 2008-05-10 14:25
    you can change many programs here to video base 16 whith this convention
    in the CON
    area add 
    CON basepin = 16




    in mainline PUB area 
    tv_pins := (basepin & $38) << 1 | (basepin & 4 == 4) & %0101



    added before the 
    tv.start(@tv_status)



    This way many demo board programs can be adapted to Hitt's OSD or other set of video pins
    etchNsketch is a good exanple

    Perry

    P.S.
    this alone does not do overlays !!!

    Post Edited (Perry) : 5/10/2008 3:00:08 PM GMT
  • TharkunTharkun Posts: 67
    edited 2008-10-05 18:00
    Hi,

    i build a Hitt-OSD (with 1881, no sync-problems) too, and it works fine when generate graphics with colorwidth(1,0) / white .

    Now i want to make a black frame around my "white graphics" using colorwidth(2,3). The only "black" i see is a grey shadow.
    (Same problem when try to generate black graphics only)

    Anyone an idea to solve this problem ?

    Tharkun

    P.S. When bypassing the diode (at pin18) with a resistor (approx.1K), the shadow changes to black, but this not the optimal solution, is it ?

    P.P.S. Thanks to Terry Hitt for this amazing OSD.

    Post Edited (Tharkun) : 10/5/2008 6:10:22 PM GMT
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