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TV Display problems — Parallax Forums

TV Display problems

Levitis LeviathanLevitis Leviathan Posts: 32
edited 2006-08-27 21:19 in Propeller 1
When I first wired up by Propeller breadboard system, I was able to get the display.spin program to run correctly. Now that I am going through the examples in the book step by step, I cannot get ANY output on the TV. I've tried several tv's and patch cables with the same results. I am using the 5 mHz external crystal. I have double checked that no wires are loose or misconnected, and have even verified the resistor values with a multimeter. Are there any others having similar problems? Are there any voltages which should be present at the chip output pins to verify that it's not a bad chip videowise?

Comments

  • SawmillerSawmiller Posts: 276
    edited 2006-08-25 02:37
    have you taken the resisters out of the breadboard/circut and put them back in ? are you on the right pins ? the A12-14 pins that the display program calls for are not the physical 12-14 pins it's more like physical 17-19 or some such ( at work right now , would look at the propstick label...)
    if all that is ok.. you could try to run 2 cogs with a blinking led in each to check the chip.... I went and accidentally put 10v to a pin and after that i could not get more than one cog to run ( which you need for the tv-display ) the chip would still blink bunches of leds, but i could not get it to run more than one cog..
    dan
  • glentechglentech Posts: 35
    edited 2006-08-25 16:09
    If you have made this up on a solderless breadboard I would suggest making sure you have a capacitor of sufficient size between + and - as I had some wierd problems until I made sure my power supply was working properly. Everything worked at slower speeds but something would go haywire at the 5mhz pll16 setting.
  • Levitis LeviathanLevitis Leviathan Posts: 32
    edited 2006-08-26 03:50
    I've verified that the correct physical pins are connected, and that blinker.spin runs correctly with multiple cogs. Input voltage is 3.3 vdc regulated from a wall wort converter.

    I thought about the power supply issues, since when I had initial success with tv output I was using 3.75 vdc from three AA batteries. I tried the battery route again without success.

    I'm going to replace the resistors and associated wiring to the rca connector tomorrow.
  • glentechglentech Posts: 35
    edited 2006-08-26 16:22
    It takes more than just a wall wart I'd say. My experience is that it takes a capacitor on the breadboard. What size are you using? I'd say at least a 10uf as it seems to dampen some sort of feedback that happens on the fast speed setting. It could be this is not your problem. Just some ideas cause I thought my chip was bad. There is an old thread somewhere you might want to read.
    http://forums.parallax.com/forums/default.aspx?f=25&m=136976&g=137109#m137109

    Also have you tried running blinker.spin at 80mhz to make sure it is working at that speed?
  • Levitis LeviathanLevitis Leviathan Posts: 32
    edited 2006-08-27 03:30
    glentech:
    I read the thread referenced, and I do have a 1 uF cap across Vss and Vdd in conjunction with the LM317T voltage regulator on the breadboard, so the chip isn't being powered by the wall wart alone.

    I tried the blinker.spin program and it does NOT work with the xtal1 + pll16x code, though it runs with xtal1 + pll4x and 8x (very much like the problem you raised in the thread.) However, if I run the same program without this line of code, the leds all blink at the apprpriately rapid rate.

    Are you suggesting the 10 uF be subbed for the 1 uF across Vss and Vdd?
    Thank for your for assistance with this tricky problem. I'm wondering if the 5.0 MHz xtal didn't go bad...
  • glentechglentech Posts: 35
    edited 2006-08-27 04:56
    Well not being in front of my project I can't remember the exact size i used but I remember that when I Put the larger size capacitor on it was just like magic and my vga monitor came to life. I think I left the 1uf connected and put the big one on with it. So yeah I'd suggest at least trying it.
  • Levitis LeviathanLevitis Leviathan Posts: 32
    edited 2006-08-27 20:26
    glentech: Tried 1 uF, 10 uF and even 100 uF caps and nothing works at xtal1 + pll16x.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2006-08-27 21:19
    A 10uF tantalum cap on the regulator's output, located very near the regulator, should be adequate for filtering. But just a filter cap on the regulator is not enough. You also need at least one ceramic bypass cap (0.1uF) from Vdd to Vss right at the pChip's Vdd and Vss pins and with the shortest leads possible. Two of them (one on either side of the DIP40) certainly wouldn't hurt.

    If your wall wart is filtered, put a 0.1uF cap on the input side of the LM317. If it's not filtered (e.g. designed for a battery charger), 1000uF on the '317's input wouldn't be too much. (You can tell whether it's filtered or not by looking at the wall wart's output on a scope. If it's smooth with a slight 120Hz ripple, it's filtered. If the voltage goes to zero periodically, it's not filtered.)

    -Phil
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