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LaPOD: Low cost Logic Analyzer probe for MSO5k, DHO900 and more!

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ebastler:

--- Quote from: UK on November 03, 2023, 09:47:40 am ---
--- Quote from: ebastler on November 03, 2023, 09:20:18 am ---Edit: What's wrong with mini-HDMI?  ;)

--- End quote ---
1. It's double as weaker than full-sized HDMI, while HDMI itself is not the strongest one.
2. Poor range of cables, their availability, and a bit higher price.

So I prefer to pay extra once for a taller IDC header than for useless mini-HDMI cables if this could count as an argument.

--- End quote ---

Both are valid points to consider, of course, but I don't see show-stoppers there. Mini HDMI is specified for 5000 plugging cycles vs. 10000 for full-size; seems more than enough for me. (Remember, you are not allowed to hot-plug the Rigol logic probes anyway!) And four cables including shipping start from 8.50€ on AliExpress or 12€ on Amazon, and there are many offers.

So I don't know about "useless" for mini-HDMI... But isn't it nice that we can have different breakout boards easily, all using the same pods with full-size HDMI plugs?  :)

UK:

--- Quote from: ebastler on November 03, 2023, 10:15:13 am ---Mini HDMI is specified for 5000 plugging cycles vs. 10000 for full-size; seems more than enough for me. (Remember, you are not allowed to hot-plug the Rigol logic probes anyway!)

--- End quote ---
Weaker meant not about plugging cycles, but the rigidity and strength of the connection, as well as the gripping force of smaller contact pads... since that's not a connection behind your TV (where nothing happens), it is a workbench and you can easily do !!!hot-unplug!!! just by accident while using the LA. That's why earlier I suggested a full-sized DP-port with its fixing feature.

Summarizing the arguments above, reducing the size of the connector increases the chance of accidents!


--- Quote from: ebastler on November 03, 2023, 10:15:13 am ---So I don't know about "useless" for mini-HDMI... But isn't it nice that we can have different breakout boards easily, all using the same pods with full-size HDMI plugs?  :)

--- End quote ---
All my photo and video stuff use micro-DP or micro-HDMI and it is more common nowadays, several 4th and newer 5th PIs also use micro-HDMI... that's why it's useless cable.


--- Quote from: ebastler on November 03, 2023, 10:15:13 am ---And four cables including shipping start from 8.50€ on AliExpress or 12€ on Amazon, and there are many offers.

--- End quote ---
When I'm talking about availability I mean I don't want to wait about a month for delivery from Alixresss :-DD

After all, if we back to the beginning main oliv3r's point was the versability when you can take any HDMI cable lying around and use it with LA and that's really cool! And mini-HDMI is not cool at all, except for the size of the connector.... moreover, overall savings are just a couple of millimeters at the sacrifice of reliability and rigidity of the connection.

ebastler:
Alright -- many of these aspects are a matter of personal preferences, I think.

I would definitely prefer to have a complete set of probes, cables and grabbers in the drawer anyway, so re-using existing cables is not important to me. While the micro-HDMI connectors feel flimsy to me, mini-HDMI seems sturdy enough. And yes, I would probably also be too impatient to wait for AliExpress delivery; so I'd spend the extra 3.50€ to get four cables from Amazon...

Anyway, the nice thing is that we don't need to make a hard-and-fast decision here, but can have both versions of the breakout board. If oliv3r prefers a different solution, I could always roll my own mini-HDMI version. (Or go with the 2*8 probes and fine-pitch ribbon cable; still pondering on that decision...) :)

oliv3r:

--- Quote from: ebastler on November 03, 2023, 08:28:01 am ---One more comment, if I may, regarding the LMH7324-based pod from reply #155:

The blocking capacitors for the various supply voltages are place a bit too far away from the LMH7324, for my taste. Especially when considering that we are already making compromises with the inductance by using the larger 0603 parts and 100 nF caps only (as used by Rigol too), vs. the (additional?) 10 nF suggested '7324 datasheet.

--- End quote ---
I got them as close as I could, there's traces underneath for power already, so dropping them isn't an option really. The caps are 6mm away, which I admit is further then I'd prefer too. Also, I really wanted to avoid via's, as that introduces other problems of course. There's always the possibility to add extra caps at the bottom though, like what dren.dk did, but I didn't want to compromise on the heat dissipation ability, as the bottom plane is where the ground plane gives the heatsink, adding those capacitors reduce that by quite a bit.

The only real alternative I can come up with, is route the signals on the left/right outside, and keep the top area for the capacitors, but that would make the traces considerably longer, about 3x as long is my guess. So then I ask you, is that worth it? Is it okay to have traces that are 3x as long?

oth, they are on the differential side, and adding a few cm shouldn't be a big issue. Let me mull on that for a bit.


--- Quote ---If you drop the differential output signals down to another layer right away, you would have room for the capacitors directly to the left and right of the '7324. You could bring the differential signals back to the top layer in a convenient place, just below the RN1 and RN2 arrays. That would also allow you to use arrays for the 220 Ohm termination resistors, placed just below RN1 and RN2 respectively.

Oh, and one more thought: When length-matching the four channels on the pod, it should be sufficient to make the total of "trace length on the input side + differential trace length on the output side" equal for all channels. It looks to me like, at the moment, you have separately balanced everything on the input side, and also on the output side. Maybe you can save a few wiggles and some PCB space?

--- End quote ---
All traces, from the 50 pin connector, to the output pin, should all be exactly the same length for each signal ;) I didn't length match pairs only, For obvious reasons, if I measure a 2 channel signal, across 2 pods, I don't to care which input is matched, but want to ensure the delay is identical everywhere. That's why some of the lines look a bit weird, while not being snakes, because they are length matched too.

oliv3r:

--- Quote from: UK on November 03, 2023, 08:32:12 am ---
--- Quote from: ebastler on November 03, 2023, 07:31:17 am ---But I took a photo from the net and used the connector width for scale -- attached.

--- End quote ---

Your illustration has a bit of a smaller scale... here is a real scale of 85mm, and a vertical port illustration as well.
Still do not realize why you think that vertical HDMI ports look ugly since most of the Rigol scopes have vertical USB ports on their front panels, even Rohde & Schwarz have the same.

--- End quote ---
Very true :D just the parts themselves I suppose, and it'll make the breakout board 'fat' :p idk, just a feeling if anything.

I'll print the current draft on paper, and see how it fits on the mso5000; doing a mini HDMI breakout for the DSO900 is a fun exercise :) and nice to have. The vertical jacks though, they make sense logically, as it also saves on using via's :p but the extra depth, extra height put me off. I even liked the vertical connector idea, but those special IDC connectors make me a bit cringe :p

So with all the feedback, I'll start again, bring caps closer, increase the width to fit the plastic, do a mini hdmi variant :p

edit: Suppose if you've done it 8? times, it goes a lot faster :p

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