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TV Output resistors values? — Parallax Forums

TV Output resistors values?

jmspaggijmspaggi Posts: 629
edited 2010-11-13 02:09 in Propeller 1
Hi,

For the TV Output on the PPDB, the resistors are 1100, 560 and 270.

I have thousands of resistors, but not those values :(

The closest I have are:
For 270 => 220 and 330.
For 560 => 330 and 470.
For 1100 => 1000 and 1200.

So my question is:
Can I go with 1000, 330, 220 instead of 1100, 560, 270? Or does those values need to be accurate?

Thanks,

JM

Comments

  • LeonLeon Posts: 7,620
    edited 2010-11-12 06:05
    Just buy the right ones, they don't cost much. Of course, you could always build up something close by putting the ones you have in series and parallel; I think there is software around to do the sums for you.
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 06:08
    But if I buy some, I will not have them before Monday ;)

    Do you have any link for a software able to help me with that? Else I will try to do some calculation.

    Thanks,

    JM
  • LevLev Posts: 182
    edited 2010-11-12 06:25
    @JM
    (2) 2.2k resistors in parallel will give you 1100 ohms. A 220 and 330 in series is 550 ohms which is probably close enough. Add another 10 ohm resistor in series , if you have one, to get a nominal 560 ohms. If you have any 100 ohm resistors, put one in series with (2) 330 in parallel to get 265 ohms, which is close to 270.

    Lev
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 06:32
    I have 10 ohms, I have 100 ohms, I have 2.2k... Look like I have all what I need! Super!

    I even have 1 ohms so I can put 5 in series for 265 ;) Or 2 x 10 ohms parallel.

    Thanks. I will try that right away!

    JM
  • AribaAriba Posts: 2,690
    edited 2010-11-12 07:06
    It will work also with:
    220, 470, 1000 Ohm

    The values are not that critical, they just must build a 3 bit DAC, so the relation must be near to 1:2:4.
    If you want it exact, use two 470 in parallel instead of the 220R.

    Andy
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 07:11
    Ok! I see!

    so I can you an R value with 2 R in parallel, 1 R and 2 R in series?

    It's already too late, but if what I just did is not working fine, I will try that way.

    Thanks,

    JM
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-11-12 08:31
    As long as you are not trying to make some sort of test generator then as close as possible will be ok. I have always used 220, 470,1k2 as I usually only have E12 series resistors here.
    Usually it is one of those bags of 600s, 10 of most values.
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 08:47
    I just figured my mistake :(

    I'm using this breakout board: http://www.sparkfun.com/commerce/product_info.php?products_id=8826 and there is 3 pins. I thought BRL and BRK are the same so just choosed one randomly.... Wrong choice :(

    So I'm back with the solution Lev proposed since I already soldered it and it's now working fine.

    Thanks all for your help.

    JM
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 09:45
    Finally, it's not working ;)

    It worked for 30 seconds then the display stopped.

    I just plugged back the option with the 5 x 470 and seems to we working fine (way longer than 30 seconds).

    So back to the soldering iron. Just to bad I already soldered the RCA Jack to the breakout bord, else I will have make my own board with it.

    JM
  • Cluso99Cluso99 Posts: 18,069
    edited 2010-11-12 15:40
    Phil is the expert here, but I would thave thought 222, 470, 1000 would have been close enough. However, from Phil's comments in other threads, some monitors cannot handle a non-true 75 ohm impedance. He suggested a resistor and capacitor across the output to ground. IIRC 191R and 100pF. So I would try a 220R (which you have) across the output ans see if that helps.

    The other possibility is that the TV program is not tuned correctly, or you are outputting NTSC to a PAL monitor. You may have to tell us what code you are running.
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 17:03
    I used 470 resistors.

    2 in //.
    1 alone
    2 in serie.

    The screen is now on for hours and working fine. Just the colors which are a bit different than from the PPDB but I will adjust that on the software side. So so far I'm fine with the result ;)

    JM
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-11-12 17:14
    If your colors seem a little washed out (and they probably will be with those values), you can also add resistance across the final output terminals. I'd try a pair of 470-ohm resistors in parallel. See here:

    -Phil
  • jmspaggijmspaggi Posts: 629
    edited 2010-11-12 18:26
    Very interesting! It's to late for the board I did, but I will keep that link.

    Thanks.

    JM
  • Cluso99Cluso99 Posts: 18,069
    edited 2010-11-13 02:09
    Thanks Phil. I knew it was your baby but didn't have time to find the link.
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