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

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oliv3r:

--- Quote from: ebastler on November 07, 2023, 07:53:00 am ---
--- Quote from: oliv3r on November 07, 2023, 07:30:58 am ---So on the top-size, from the chip to the resistor/capacitor network, there's a wiggle to compensate for the length of channel 1 & 2 which come from the top of the chip, and run on the bottom side. So all traces from the chip, to the network are all 4 in identical length.  The wiggles after the network, is to match the length of the outputs going to the 2x4.

--- End quote ---

I think we are still not talking about the same traces. Referring to the attached montage, I was looking at the length-matching wiggles indicated by the two smaller circles. They seem to be for channels 0 and 3. And now you have added the wiggles for channels 1 and 2, indicated by the larger circle. These four seem to be of very similar length -- so can't you simply remove all four of them?

--- End quote ---
But I think we are :)

The yellow lines are the same four lines for all four channels, that's why the wiggles exist before the input of the resistors and caps. You could probably do some math, and reduce the bottom wiggles from the top wiggles, I certainly grant you this, but it makes it harder to raid/verify/maintain. Now you have identical wherever they are measurable. Also, making it harder, and some wiggles still remain. Also, those 'ears' on the left/right side ... plenty of space for those anyway :p Also looks a little more symmetrical this way :)


--- Quote from: ebastler on November 07, 2023, 07:53:00 am ---Edit -- some further, unrelated comments:

* I like the lowered position of the 2*4 connector; makes the vertical alignment nice and symmetrical.
* Don't forget to change the channel numbers on the top and bottom silkscreen to 0..3!
* Please correct the top silkscreen to say LMH7324.
--- End quote ---
check, check, check

ebastler:

--- Quote from: oliv3r on November 07, 2023, 09:56:48 pm ---The yellow lines are the same four lines for all four channels, that's why the wiggles exist before the input of the resistors and caps. You could probably do some math, and reduce the bottom wiggles from the top wiggles, I certainly grant you this, but it makes it harder to raid/verify/maintain. Now you have identical wherever they are measurable. Also, making it harder, and some wiggles still remain. Also, those 'ears' on the left/right side ... plenty of space for those anyway :p Also looks a little more symmetrical this way :)

--- End quote ---

Alright, I see. You prefer to match all four traces below the divider components, and then also match all traces between the divider and the LMH7324. It will certainly work; it just results in more wiggles on the board than needed. But maybe that's just an obsessive-compulsive thing for me... ;)

oliv3r:

--- Quote from: UK on November 07, 2023, 05:14:23 pm ---
--- Quote from: ebastler on November 07, 2023, 03:47:32 pm ---These connectors do not have the little tab which ensures you can't plug them in the wrong way.

--- End quote ---
Yep, it's definitely not a problem and it just could be a part of the shell.

-------

I've made a try to calculate the best dimensions for 2х2 PCB, which taking into account all shell clearances and possible margins, should have a perfect fit with both of the scopes!
Also, I want to point out that 50p header should have a slight vertical offset.

To be honest, now I'm even more interested in the version for DHO900 since I plan to get this cute little scope during the winter holidays  :-[

--- End quote ---

While I get the excitement for the vertical ports, ignoring for a moment that I used the wrong part :p, where in the world would we put the actual traces? I think even going full smd (which still requires the same amount of via's just for the holes to reach the other side, or go hybrid (smd HDMI connectors, throughole IDC connector (or vice versa) we still need a ton of via's just to route all those signals. I've also tried two options, one logical (1, 2, 3, 4) and one shortest trace (2, 1, 4, 3), which gives a rats-nest mess. What I did in the end, per your request, ordering the ports, was only possible by enlarging the PCB by half or full cm, which isn't really an option in this case?

I'd route if if I had any hopes, but with these parts, it would require going with the tiniest pitch, and probably forget about doing length-matched traces ...

oliv3r:

--- Quote from: ebastler on November 07, 2023, 10:32:52 pm ---
--- Quote from: oliv3r on November 07, 2023, 09:56:48 pm ---The yellow lines are the same four lines for all four channels, that's why the wiggles exist before the input of the resistors and caps. You could probably do some math, and reduce the bottom wiggles from the top wiggles, I certainly grant you this, but it makes it harder to raid/verify/maintain. Now you have identical wherever they are measurable. Also, making it harder, and some wiggles still remain. Also, those 'ears' on the left/right side ... plenty of space for those anyway :p Also looks a little more symmetrical this way :)

--- End quote ---

Alright, I see. You prefer to match all four traces below the divider components, and then also match all traces between the divider and the LMH7324. It will certainly work; it just results in more wiggles on the board than needed. But maybe that's just an obsessive-compulsive thing for me... ;)

--- End quote ---
Heh, my OCD says the same, but then I compromise, or convince myself, it's nicer, cleaner and more symmetric to have every measurable line matched in length. So you can pick any line on the pcb, and find its length matched trace. It just depends how you look at it I suppose :D

Trust me, my OCD is itching with the thought, I just have to convince my OCD is better then your OCD :D

ebastler:

--- Quote from: oliv3r on November 07, 2023, 10:42:14 pm ---While I get the excitement for the vertical ports, ignoring for a moment that I used the wrong part :p, where in the world would we put the actual traces? I think even going full smd (which still requires the same amount of via's just for the holes to reach the other side, or go hybrid (smd HDMI connectors, throughole IDC connector (or vice versa) we still need a ton of via's just to route all those signals. I've also tried two options, one logical (1, 2, 3, 4) and one shortest trace (2, 1, 4, 3), which gives a rats-nest mess. What I did in the end, per your request, ordering the ports, was only possible by enlarging the PCB by half or full cm, which isn't really an option in this case?

I'd route if if I had any hopes, but with these parts, it would require going with the tiniest pitch, and probably forget about doing length-matched traces ...

--- End quote ---

Umm, are you sure you have oriented the 2*25 connector the right way round? Isn't the notch, and also pin 1, facing up in the scope?

If it really needs to be flipped around, that might give you a fighting chance at routing the PCB for a "logical" HDMI connector order. It will still be very tight, no doubt about that. I agree that switching to SMD-style HDMI connectors could help a bit. (The "brick nogging" type from LCSC; they would still have through-hole mounting tabs though, which are good for stability but get in the way on all layers.)

Other degrees of freedom are rotating the HDMI connectors 180°, or moving them laterally a bit closer to the middle and moving the LEDs to the outside instead. Not sure whether either of these would help with the routing. The lateral move should at least give you a better symmetry of the trace lengths for the left vs. right connectors, requiring less overall trace length and wiggling.

EDIT: I looked again at the pinout of the 2*25 connector. It looks like it is mirrored, rather than rotated? Pin 1 should be in the upper right, I believe. -- So D0..D3 and D8..D11 will be on the right-hand side of the connector. I would definitely place their HDMI connectors on the right side too; don't see a usability problem with that.

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