and scoping is a line with sync and a white on period.
So using pal composite do I use a 50Hz interrupt to repeat the above so I get a vertical white bar.
Then there's the display odd lines every 25 Hz and then even lines every 25 Hz.
I'm not a tv engineer...faults were always caps.
Eventually hoping to get tv out like arduino to work with gcb.
Phew! That's a question that isn't easy to answer fully.
My suggestion would be that you ignore the odd-even line timing "stuff" unless you have lot's of processor power and even more time. Most (if not all) composite displays should cope without the interlaced lines. Theoretically it won't be "right", but it won't look too "wrong".
The interlace allowed 625 line resolution to be sent using the bandwith of 312.5 lines. Just send those 312.5 lines twice.
And I was a TV engineer. A very good one too. Was I ever annoyed when it became cheaper to throw sets away rather than repair them? All those years of experience, lost. Not the least part bitter about it either...
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mkstevo. Still researching the task..only out of interest. Looking up pal video and horizontal sync. and pic composite video.
I think the zx81 did all it's basic in the old crt flyback period and the rest of the time updated the display..but that was years ago.
The timing will be lots of nops for precision I guess.
I seem to remember a build yourself cross hatch generator using ttl chips in an electronics magazine,maybe eti.
I'll play with the idea until I give up...as usual :)
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Steve-"And I was a TV engineer. A very good one too. Was I ever annoyed when it became cheaper to throw sets away rather than repair them? All those years of experience, lost. Not the least part bitter about it either..."
was that crt days? I fixed a few..new tripler or sommat simple.
lcd tvs were usually caps in the switching supply... but I'm not a tv engineer.
fixing crt computer monitors was an earner once as they were too expensive to throw out.
now you can buy a pc lcd in a charity shop for £5.
a useful device I got from ebay for £5 was a component tester, identifies resistor,transistors,inductors and caps. Tells you the esr of the cap which is really useful.
mines a few years old but looks like image
I date back to valve radios and televisions. So yes, CRTs. Triplers? I had them stacked up once upon a time... I still had two universal triplers (which were actually quadruplers) when I locked up the TV workshop for the last time.
The reason that it always seems to be the capacitors in modern devices is that older "stuff" with valves ran on much higher voltages.
450V wasn't uncommon in a line output stage supply, this was often boosted by the transformer that they drove and the flyback voltage could peak at well over 5,000V. When operating correctly you could draw an inch long spark from the anode of a PL519 valve and would do so as a test to see if there was any damping in the circuit. Less than an inch meant significant loading in the output stage, or (more often) lack of resonance, usually an open circuit in the line scan circuit. These devices were far less critical of their power supplies. A capacitor could loose a significant level of capacitance (50% or more) before it had any visible effect. The power supplies were simple affairs with resistive limiting elements which meant the capacitors lived a relatively stress free [long] life.
The modern stuff runs on vastly lower voltages. 1.8V is not an unusual supply level for complex chips. That lower voltage means that it becomes, by its nature, more critical. At lower voltages the devices need far more current to operate which further stresses the supplies. Compounding this is that the PSU is almost always a switch mode one, operating in the high kHz range, 80kHz - 150kHz is not unusual. That passes a very high ripple current through the capacitors which causes them to heat up significantly which leads to losses, which leads to the capacitor aging at an exponential rate. The capacitors are much smaller physically too which just tortures them further as they can't lose as much heat through radiation. Now go back to that old capacitor which lost 50% of capacitance in the ten - fifteen year lifespan with little or no ill effect. The modern capacitor may only be able to lose 10% of its value before things start to play up, so if we had the same deterioration rate of 5% per year you can see why things struggle to last as long as they once did. And why "it's always the capacitors".
I had an ESR meter that I used frequently whilst still fixing electronics. I fitted a buzzer in mine so that I could hear it. As I tested the capacitors I didn't have to look up until the capacitor being tested sounded different. I've got one of those component testers like yours. Handy for identifying the pin outs of transistors. Although it's now as easy to fire up Google and ask it for the pin outs as it is to find where my tester is.
I used to repair anything electronic. From Kenwood mixers to camcorders, micro computers to microwaves. If it had electronics in it, you'll probably find I've attempted to fix it.
I would think that generating a PAL signal would need quite a lot of processing power, and some seriously accurate timing. At one time you could get PAL encoders that took RGB signals in and encoded them into a colour composite signal. If you are set on doing colour, that's the way I would do it. Generate one master "clock" then use it to synchronise other devices that generated the red, green and blue along with providing the colour encoder with the required signals for it to work the magic.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
you remember the deguass coil and the varistor that went oc quick. that was a problem as it went short or blew a fuse....happy days.
compo video from say a 328 like a uno can be done and I think if it can be done in arduino it can be done in gcb...I'm an optimist. I don't see the point though. acedemic..wear a mask.
tried a 50Hz isr to send h signal but scoped and maybe my usb scope is carp.
if I could set the h and v sync then read pixels from a var array... but that would mean getting bit values. I got other gcb things to sort out, so is this a priority... or a headache?
this is the isr. should go every 20ms
HI,has anyone tried to create composite video?
I looked at http://www.hpcc.ecs.soton.ac.uk/dan/pic/video_PIC.htm
and wired the resistors and scoped across 75R as display.
Tried
and scoping is a line with sync and a white on period.
So using pal composite do I use a 50Hz interrupt to repeat the above so I get a vertical white bar.
Then there's the display odd lines every 25 Hz and then even lines every 25 Hz.
I'm not a tv engineer...faults were always caps.
Eventually hoping to get tv out like arduino to work with gcb.
Phew! That's a question that isn't easy to answer fully.
My suggestion would be that you ignore the odd-even line timing "stuff" unless you have lot's of processor power and even more time. Most (if not all) composite displays should cope without the interlaced lines. Theoretically it won't be "right", but it won't look too "wrong".
The interlace allowed 625 line resolution to be sent using the bandwith of 312.5 lines. Just send those 312.5 lines twice.
And I was a TV engineer. A very good one too. Was I ever annoyed when it became cheaper to throw sets away rather than repair them? All those years of experience, lost. Not the least part bitter about it either...
mkstevo. Still researching the task..only out of interest. Looking up pal video and horizontal sync. and pic composite video.
I think the zx81 did all it's basic in the old crt flyback period and the rest of the time updated the display..but that was years ago.
The timing will be lots of nops for precision I guess.
I seem to remember a build yourself cross hatch generator using ttl chips in an electronics magazine,maybe eti.
I'll play with the idea until I give up...as usual :)
Steve-"And I was a TV engineer. A very good one too. Was I ever annoyed when it became cheaper to throw sets away rather than repair them? All those years of experience, lost. Not the least part bitter about it either..."
was that crt days? I fixed a few..new tripler or sommat simple.
lcd tvs were usually caps in the switching supply... but I'm not a tv engineer.
fixing crt computer monitors was an earner once as they were too expensive to throw out.
now you can buy a pc lcd in a charity shop for £5.
a useful device I got from ebay for £5 was a component tester, identifies resistor,transistors,inductors and caps. Tells you the esr of the cap which is really useful.
mines a few years old but looks like image
Last edit: stan cartwright 2020-09-15
I date back to valve radios and televisions. So yes, CRTs. Triplers? I had them stacked up once upon a time... I still had two universal triplers (which were actually quadruplers) when I locked up the TV workshop for the last time.
The reason that it always seems to be the capacitors in modern devices is that older "stuff" with valves ran on much higher voltages.
450V wasn't uncommon in a line output stage supply, this was often boosted by the transformer that they drove and the flyback voltage could peak at well over 5,000V. When operating correctly you could draw an inch long spark from the anode of a PL519 valve and would do so as a test to see if there was any damping in the circuit. Less than an inch meant significant loading in the output stage, or (more often) lack of resonance, usually an open circuit in the line scan circuit. These devices were far less critical of their power supplies. A capacitor could loose a significant level of capacitance (50% or more) before it had any visible effect. The power supplies were simple affairs with resistive limiting elements which meant the capacitors lived a relatively stress free [long] life.
The modern stuff runs on vastly lower voltages. 1.8V is not an unusual supply level for complex chips. That lower voltage means that it becomes, by its nature, more critical. At lower voltages the devices need far more current to operate which further stresses the supplies. Compounding this is that the PSU is almost always a switch mode one, operating in the high kHz range, 80kHz - 150kHz is not unusual. That passes a very high ripple current through the capacitors which causes them to heat up significantly which leads to losses, which leads to the capacitor aging at an exponential rate. The capacitors are much smaller physically too which just tortures them further as they can't lose as much heat through radiation. Now go back to that old capacitor which lost 50% of capacitance in the ten - fifteen year lifespan with little or no ill effect. The modern capacitor may only be able to lose 10% of its value before things start to play up, so if we had the same deterioration rate of 5% per year you can see why things struggle to last as long as they once did. And why "it's always the capacitors".
I had an ESR meter that I used frequently whilst still fixing electronics. I fitted a buzzer in mine so that I could hear it. As I tested the capacitors I didn't have to look up until the capacitor being tested sounded different. I've got one of those component testers like yours. Handy for identifying the pin outs of transistors. Although it's now as easy to fire up Google and ask it for the pin outs as it is to find where my tester is.
I used to repair anything electronic. From Kenwood mixers to camcorders, micro computers to microwaves. If it had electronics in it, you'll probably find I've attempted to fix it.
I would think that generating a PAL signal would need quite a lot of processing power, and some seriously accurate timing. At one time you could get PAL encoders that took RGB signals in and encoded them into a colour composite signal. If you are set on doing colour, that's the way I would do it. Generate one master "clock" then use it to synchronise other devices that generated the red, green and blue along with providing the colour encoder with the required signals for it to work the magic.
you remember the deguass coil and the varistor that went oc quick. that was a problem as it went short or blew a fuse....happy days.
compo video from say a 328 like a uno can be done and I think if it can be done in arduino it can be done in gcb...I'm an optimist. I don't see the point though. acedemic..wear a mask.
tried a 50Hz isr to send h signal but scoped and maybe my usb scope is carp.
if I could set the h and v sync then read pixels from a var array... but that would mean getting bit values. I got other gcb things to sort out, so is this a priority... or a headache?
this is the isr. should go every 20ms
Last edit: stan cartwright 2020-09-15