Project: HDMI/DVI out for STFM

[exxos]

Do you know of a schmitt buffer that can also do 3.3 -> 5v level translation though? That's the thing.

Any buffer will do that pretty much... The buffers are use on my STE booster are basically being driven with about 3V input... Because the rise and fall times of the GAL are pretty slow so it never reaches the full 5V...

The buffer chip runs on 5V.. And outputs a nice 5V to the CPU. As it is a schmitt buffer, its hysteresis extremely good and it filters out any tiny noise or glitches in the signals.

I did actually try regular buffers and they were frankly terrible in comparison.

[Smonson]

This is a comparison between the original (regular logic) buffer, and the clock fanout buffer at 16MHz. It's clear that the new one is a more forceful driver. The clock on the 68k pin is quite rounded still, I think 100 ohms in series is a bit on the high side to get any benefit from the squarer signal coming out of the buffer. The signal going into the buffer is also pretty sine-y after passing through the series resistor and the ribbon cable, I can experiment more with lower resistor values at some point.

old-clock.png

new-clock.png

Speaking of Schmitt triggers, do you mean something like SN74LVC1G17? I'll add a few to my next mouser order and can test one out and see how it goes.

[exxos]

This is a comparison between the original (regular logic) buffer, and the clock fanout buffer at 16MHz. It's clear that the new one is a more forceful driver. The clock on the 68k pin is quite rounded still, I think 100 ohms in series is a bit on the high side to get any benefit from the squarer signal coming out of the buffer. The signal going into the buffer is also pretty sine-y after passing through the series resistor and the ribbon cable, I can experiment more with lower resistor values at some point.

The resistor value just be there to stop the ringing.. You're not far off with your bottom image anyway.. Somewhere around 33R is normally a good value.

Speaking of Schmitt triggers, do you mean something like SN74LVC1G17? I'll add a few to my next mouser order and can test one out and see how it goes.

Yeah I think that is the one I am using on my booster....

It gets driven by something like a 1.5V - 3.5V sinewave on its input (from my GAL) and it cleans it up to a really nice square wave at 40MHz to the 68K CPU.

I normally take scope readings of things like this, but I cannot see it in my thread :(

[Smonson]

I'd like to take an informal poll, if anyone who has an opinion would care to respond -

Which video connector would you prefer to see on this mod: HDMI or DVI?

HDMI connectors are cheaper and use less board space (and need a smaller hole in the back of the ST). But the DVI connector seems a lot more physically sturdy.

Both types of connector carry the same signals and both are compatible with DVI and HDMI monitors and TVs.

In either case, audio would not be transmitted through the connector - just to be clear.

[exxos]

Didn't you say one connector was under licencing or something a while back ?

[Smonson]

Yes but I don't think anyone is really going to care, since I'm not a company.

...Right?

[exxos]

Yes but I don't think anyone is really going to care, since I'm not a company.

Yeah.. true.. only the flack I get off companies for doing nothing is unreal :roll: There was a company to verify the quality of some goods I use.. I mentioned that on my website.. then they sent me a letter last week saying I didn't have permission to do that unless I paid them.. no thanks.. Bit pointless having a company to verify products then not being able to mention them! Just greedy companies as usual..


Anyway..

I see the advantages of the larger connector with it being more robust.. But in case of connections on monitors, I'm not even sure what my it is used a larger connector any more...? My cheap TV uses a smaller HDMI connector.. So I end up doing this..

IMG_3399.JPG

So I think having the smaller connector probably more of a advantage.. Of course it may not be as strong, but we can look into options or different manufacturers of connectors to see which is the strongest one..

Of course the workaround for licensing issues, will be to not supply the connector with the board.. I don't think it is a problem to buy and sell the connectors themselves... But using that connector on a actual product would be a licensing infringement.. It may be worth looking at their licensing terms, see if there is a workaround like low-volume or prototypes can be used without licensing...

But yes, nobody should really care, but I thought that about my web shop when someone reported me got me shut down.. Only takes one person looking to cause trouble.. And I have had many over the years :(

[rpineau]

I'll also go HDMI for convenience.

[IngoQ]

I'd say stick with the DVI, just to make sure. If size is a matter you can always go with MiniDVI or MicroDVI. In addition, DVI-I would allow you to output both analog and digital RGB on the same connector.

DVI to HDMI Adaptors are cheap as chips, and could even be included, in my mind not worth the risk of a costly cease and desist letter.

[PaulJ]

I'd like to take an informal poll, if anyone who has an opinion would care to respond -

Which video connector would you prefer to see on this mod: HDMI or DVI?

HDMI connectors are cheaper and use less board space (and need a smaller hole in the back of the ST). But the DVI connector seems a lot more physically sturdy.

Both types of connector carry the same signals and both are compatible with DVI and HDMI monitors and TVs.

In either case, audio would not be transmitted through the connector - just to be clear.

Personally I'd like to see an HDMI connector. Most things today have an HDMI input and if not there are plenty of HDMI to DVI cables available.