Expansion port 5V ampage

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Vampire
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Expansion port 5V ampage

Post by Vampire »

I've made up a SCART converter + tape VSync box from my Atmos, the 74HCT244 one. Looking at the expansion port specs, its got a 5v line on it, so I was thinking about using that instead of an external power supply.

I have no idea how much drain that converter puts on the external PSU, or how much interference its going to cause. Has anyone tried using the expansion port to power one, or is that going to brown out/fry the Oric board?

Its my original machine (it replaced my oric1 in 83 or so) and I'm loathed to blow the poor thing up.

Vampire^TZT
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Post by Dbug »

I guess you are refering to this particular schematics: http://andre.cheramy.net/trucs/peritel2.pdf ?

Have you been trying it already ,with an external PSU, does the result look good?
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Post by Vampire »

Yeah, thats the one I've made. I just decided to bite the bullet and go with board power. There have been no ill effects so far.

The image quality is excelent. Had two issues to begin with though. One was my TV (only one of the scart inputs is RGB, the other only supports composite) and the other was my guff soldering on the green circuit (bridged to ground). There's a small amount of fringing on the black to white at the top, left of the screen, but that may be more to do with my Oric as the edges on the rest of the screen are super crisp. There is next to no interference vissible on border signal, as opposed to RF out that has all that noise over it.

If anyone is interested, I can post pictures and VeeCad files for the stripboard design once I have the audio interface finished. I'm making a partner box that allows me to swap between vsync and tape at the flick of a switch. It also lets me put the Oric audio through the TV.

I'm also more than willing to post my PC tool chain if anyone thinks it would be of use.

Vamps.
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Post by Dbug »

Sure, if you send me all by mail, I can host that somewhere on the site, so we guarantee it will not go away any-time soon.

The board stuff I can add to the original page describing the schematics, the tool chain can go on the ftp and be linked from the "cross development" tools forum.
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Post by Vampire »

Cool. I'll get that all sorted over the weekend. I'll include the sample code I've done for detecting the VSync too. I couldn't find it anywhere else on the site, so I kinda borrowed from Buggyboy ;)

I've just finished boxing it all up, which includes my little switchable VSync box too, and it works great.

The last problem I have is to do with the SCART sound. It works fine, but there isn't enough resistence across the line to trigger the internal speaker cut off. I know it works because it cuts the speaker when plugged into my PC. I'll have a little play and see if I can rectify this.
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Post by Twilighte »

Vampire wrote:The last problem I have is to do with the SCART sound. It works fine, but there isn't enough resistence across the line to trigger the internal speaker cut off. I know it works because it cuts the speaker when plugged into my PC. I'll have a little play and see if I can rectify this.
Interesting. I had (as with most people) assumed that the internal speaker could only be disabled in two ways. Either physically removing it or placing a rather questionable short across the sound output on the Cassette port connectors. :?

Oh and some devious people put a variable resistor across the connector so providing a crude volume control. :twisted:

I didn't think plugging the output into a pc would cut the internal speaker. For many years i used an external amplifier to listen to my Oric, i remember that didn't "cut off" my internal speaker so i disconnected it internally.

If your saying its possible to cut it off without making any internal mods then i'd certainly be interested. :shock:

I'm also very interested in the finished box and internals that Dbug offered to host. :)
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Post by Vampire »

Twilighte wrote:I had (as with most people) assumed that the internal speaker could only be disabled in two ways. Either physically removing it or placing a rather questionable short across the sound output on the Cassette port connectors. :?
I've been looking at the schematic here, and its pretty ropey. I can't make out much detail round the speaker out other than the pin 4/5 line in the tape port comes from before the internal amplifier (i.e. line out).

Now, that reminded me that I have the original Oric-1 schematic from the center spread of Oric Owner #5 (which I will scan if someone wants me to). And It shows nothing special round that way, other than its not got the entire LM390 amp on it?! I figure that my laptop is pretty much shorting pin 4 to ground, which is cutting all signal from the internal amplifier?

In other news, I've sent the stuff to Dbug already :)
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Post by Dbug »

I updated the video converter page:
http://www.defence-force.org/computing/ ... /index.htm

I fixed the issue with the 75HCT244 (should have been a 74HCT244), and added a photo of Vampire's own version. You can also download the designer files for VeeCAD on the same page.
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