Hello,
I've been trying to control an old AppleColor RGB Monitor specs are here using Arduino, but I'm having a hard time understanding the concepts of "Composite sync., negative going TTL" (I took that from the above website).
What I want to do in the end I believe is not that hard. I want to fill the monitor with a solid color. I don't want to draw text or anything.
Based on this thread and using a VGA monitor, I was able to simulate a VGA signal and it is working nicely, but the thing is that I have 12 old (non-VGA) AppleColor RGB Monitor that no longer have any use and I was thinking about using them in an art piece I'm making.
VGA monitors have 2 different pins for Horizontal and Vertical sync, but the AppleColor only has one that is called "Composite TTL sync" (pin number 3).
So my question is:
Is it possible to put this monitor in sync using an Arduino? Any hints on how this could be done?
Any help is greatly appreciated. Thanks a lot!
Luckygoose
I found a little information on the RS-343 Standard that according to your link this display uses: [RS-170 video signal]
RS-343
RS-343 is an EIA (Electronics Industries Association) standard for non-broadcast high resolution monochrome video. RS-343 was introduced later than RS-170 and intended, according to the title, as a signal standard for "high-definition closed-circuit television", which among other things reduced the signal amplitude to 1.00 Vp-p. The signal specifications according RS-343:
White: +0.714V
Black: +0.054V
Blank: (0V reference)
Sync: -0.286V
RS-343 specifies a 60 Hz non-interlaced scan with a composite sync signal with timings that produce a non-interlace (progressive) scan at 675 to 1023 lines.
OK I'm guessing here, but most experimenting is putting forward a hypotheses and testing it so here it is.
Composite sync means that there is only one clock signal for all data transmission signals. This is probably a TTL level square wave that alternates between ground and a value set by the spec. (according to the data above -0.286V)
Now! the challenge is what is Negative going TTL.... well negative is all relative to whatever 0 is... looking at the spec that would be the blank signal or the 0V reference. On your connector there is nothing labeled this way but it may either be shell shield ground or composite sync return... time to get out the multimeter and see how those return pins compare to the shell (case ground).
I'll keep poking around, when you find a term you don't understand.... GOOGLE
Lets see who else jumps on this to give you awesome advice.
Oh, and don't get hung up on the fact that the spec was originally monochrome, it's pretty common to add more channels to a monochrome video format to make it color.
Wikipedia cleared a little up for us this is an RGB connection... pay careful attention to when it talks about RGBS which is what I think we're dealing with. If so your monitors may be very much like a SCART interface for which there should be lots of info on the internet.
RGB analog component video
The various RGB (red, green, blue) analog component video standards (e.g., RGBS, RGBHV, RG&SB) use no compression and impose no real limit on color depth or resolution, but require large bandwidth to carry the signal and contain much redundant data since each channel typically includes the same black and white image. Most modern computers offer this signal via the VGA port. Many televisions, especially in Europe, utilize RGB via the SCART connector. All arcade games, excepting early vector and black and white games, use RGB monitors.
Analog RGB is slowly falling out of favor as computers obtain better clarity using digital video (DVI) and home theater moves towards HDMI. Analog RGB has been largely ignored, despite its quality and suitability, as it cannot easily be made to support digital rights management. RGB was never popular in North America for consumer electronics as S-Video was considered sufficient for consumer use, although RGB was used extensively in commercial, professional and high-end installations.
RGB requires an additional signal for synchronizing the video display. Several methods are used:
composite sync, where the horizontal and vertical signals are mixed together on a separate wire (the S in RGBS)
separate sync, where the horizontal and vertical are each on their own wire (the H and V in RGBHV)
sync on green, where a composite sync signal is overlaid on the green wire (SoG or RGsB).
Composite sync is common in the European SCART connection scheme (using pin 17 [gnd] and 19 [out] or 20 [in]). Sometimes a full composite video signal may also serve as the sync signal, though often computer monitors will be unable to handle the extra video data. A full composite sync video signal requires four wires – red, green, blue, sync. If separate cables are used, the sync cable is usually colored white (or yellow, as is the standard for composite video).
Separate sync is most common with VGA, used worldwide for analog computer monitors. This is sometimes known as RGBHV, as the horizontal and vertical synchronization pulses are sent in separate channels. This mode requires five conductors. If separate cables are used, the sync lines are usually yellow (H) and white (V),[2] or yellow (H) and black (V), or gray (H) and black (V).[3]
Sync on Green (SoG) is the least common, and while some VGA monitors support it, most do not. Sony is a big proponent of SoG, and most of their monitors (and their PlayStation 2 video game console) use it. Like devices that use composite video or S-video, SoG devices require additional circuitry to remove the sync signal from the green line. A monitor that is not equipped to handle SoG will display an image with an extreme green tint, if any image at all, when given a SoG input.
Hello!!
First of all thanks a lot Nate and Richard. It is great to get some help on this matter. Pretty much everything here is quite new to me.
@Nate:
I also believe that the monitor is using RGBS, but honestly I never heard about SCART. I will take a look at it.
Thanks a lot for the RS-343 description. Let's see how I could put that to use.
However, Arduino should not be asked to source more than 20mA from an output pin, and video systems are designed with a 75 ohm load resistance (by definition). So you will need a transistor (a jelly-bean part like 2N2222 or something) to produce a good 5V signal with a 75 ohm source impedance.
Would you mind telling me what is a "75 ohm load resistance"? How do I produce a "75 ohm source impedance"?
Should I connect a 75 ohm resistor from 5V to the collector of a 2N2222 transistor, the emitter to ground and the base to one of the Arduino's pin?
I guess I understand now what "75 ohm load resistance" means. Here it goes:
It means that the monitor (or TV) has an internal 75 ohm resistor inside it, so one should take it into account when supplying voltage to the monitor, especially if you need to provide a precise amount of voltage (which appears not to be the case with this specific monitor).
Arduino should not be asked to source more than 20mA from an output pin, and video systems are designed with a 75 ohm load resistance (by definition).
This statement was also a bit of mystery to me... But I guess it means that based on the formula V=R*i, if using 5V from Arduino and with the 75 ohm load resistance from the monitor, this would draw 60mA from the Arduino pin, which would be more than recommended. Is that right?
I would first confirm that those inputs to the monitors measure 75 ohms each from the input to the monitor ground.
Remember we are talking about impedance not resistance. Often video inputs have a series capacitor to block DC, so while they will look like a 75R impedance they will not measure it with a simple resistance meter.
