The Definitive Dual Res Monitor Switching Circuit (for X68k)

[segasonicfan]

Here is a really useful little circuit I came up with. It instantly switches the 31khz/15khz sync between outputs using the HD detect pin on the ISL59885. Moreover, this IC corrects all sync pulses and standardizes them (my downscanner would not work without it!)
The great benefit of this is that it can save your low-res CRT from damage and from the inconvenience of not knowing which mode your game is on boot. Just plug in 2 monitors (a VGA and low res CRT) and watch it swap the signal between the two! Great for MAME setups that have video cards set to 15khz (but they still boot at hi-res) and also works great on my Extron VSC500 downscaler using a KVM switch on my 36" low res CRT

some pics of my board:




-Segasonicfan

[undamned]

Nice work, sir!
-ud

[jskyboo]

Very cool little circuit!

[Ed Oscuro]

Seems pretty cool - though I don't think people should be risking damage to their monitors anyways. If uncertain, there's emulators or the 31KHz monitor, instead of blindly plugging into the 15KHz set.

[lettuce]

Seems pretty cool - though I don't think people should be risking damage to their monitors anyways. If uncertain, there's emulators or the 31KHz monitor, instead of blindly plugging into the 15KHz set.

Or just get a J-PAC if using a 15khz monitor

[segasonicfan]

Seems pretty cool - though I don't think people should be risking damage to their monitors anyways. If uncertain, there's emulators or the 31KHz monitor, instead of blindly plugging into the 15KHz set.

the entire point of this circuit is that eliminates the risk of monitor damage. that's the exact reason I built it.

Or just get a J-PAC if using a 15khz monitor

not a bad idea, though it is $59 + ship where as this circuit costs about ~$5. Also the J-PAC is really overkill for a X68000 application (if if would work for that at all) and I like having this in a small little box. Also the J-PAC doesnt have two monitor outputs, so you would have to disconnect it constantly if using an X68000.

I don't know what Sync processing the J-PAC uses but I wonder if it has the abilities of the ISL59885 for correcting the wacky stuff coming from PCBs. This is the chip JROK uses in his Sync Cleaner boards and as far as I know is the best thing out there for the job.

-Segasonicfan

[Ed Oscuro]

I said "should," not "solved for Murphy's Law." What you've made is of course useful and highly recommended, but I think that it should still be highlighted that people ought not to plug in without being aware of what signal they are getting and what hardware they are trying to display it on. That's all I meant.

[jskyboo]

Does anyone know if a similar simple circuit could be built to detect and switch 240p and 480i? It would be awesome to be able to extend this to switch between 240p/480i/480p.

[segasonicfan]

One could, but it wouldn't be with this chip. This chip "senses" H sync levels over 24khz and then switches. That means it won't work to switch different low-res signals.