triofrog.blogg.se - Composite for sync checker

#Composite for sync checker serial
#Composite for sync checker portable
#Composite for sync checker series

After about 10 seconds of waiting, most of the normal startup text appeared along with some garbage characters, and in some cases automatically typed load/run commands (second picture). The most common outcome was an empty blue screen with borders (first picture).

Other video devices don't have problems with this TV.Ī) Does my assumption make sense (i.e.Caused various abnormal startup screens, including a simple black screen on a couple of boots.

No resistor causes sync failure, but faint grey pixels can be seen tumbling and rolling.įrom these findings, I'm assuming that I've bought a TV without an internal 75ohm resistor.

33k to ground gives a picture with muddy grey instead of whites.

75ohms to ground gives a nice picture with bright whites.

To cut a long story short, it will only work when there's a resistor to ground (as shown in the very first diagram in the thread).

#Composite for sync checker portable

Transistor type might want looking at to make sure it has the frequency range the 2222 was conveniently to hand.įor further testing of my TellyMate project (which uses the 2-diode, 2-resistor circuit above), I bought an old 5" portable 12v telly from a car-boot sale this morning (Â£2 - bargain!). This version - if I got my sums right! - should have two volts p-p at the base of the transistor, offset by the diode voltage drop to offset the Vbe drop it *should* give a low-impedance output protected by the 75 ohm in-line resistor into 75 ohms.

When both are at 5v, you're driving 75 ohms from 1000//330 = 248 ohms result is 1.16v If you're driving into 75 ohms, using Rsync as 1000 and Rvid as 330 ohms, when vid = 0 and sync = 5v, you're driving into 75//1000 = 61 ohms and the result is 0.28v. The analysis is not as straight-forward as you might think as there are return paths to ground through the resistor which is not being driven. Terminate with the TV's input resistor - but be aware that older TVs may have a live chassis!. In practice I do it exactly the same way you did, and tweak the resistors till it looks right.

#Composite for sync checker series

*Strictly* what you should be doing is deriving a 2.0v p-p signal and outputting that through a series 75 ohm resistor from a low-impedance source - a voltage follower or similar.

Am I safe, or do I need to check the batteries in my fire alarm?Īre there any simple improvements to the above circuit? It meets my target of 'simplicity', but should I be 'balancing' the signal or anything like that? Do I need a 75ohm resistor in series with the output? It produces a much whiter output and the TV hasn't blown up so far. The 75ohms is implied at the other end of the cable (inside the TV):Īm I right? Is the second circuit "correct"? In a fit of recklessness, I removed the 75ohm resistor from my circuit and tried it. I now believe that this circuit shouldn't have the 75ohm resistor in it. The problem is that the 'white' is very 'grey': Two output pins one sync, one pixel data. I used a project at serasidis as the foundation of the circuit. It produces a Black and White PAL composite video signal.

#Composite for sync checker serial

My 16x2 LCD serial backpack (a great project - thanks microcarl!) is becoming just too small for debugging with, so I've made myself a serial->TV display device.