Products > Test Equipment
LaPOD: Low cost Logic Analyzer probe for MSO5k, DHO900 and more!
ebastler:
--- Quote from: Mechatrommer on December 02, 2023, 12:46:28 pm ---just now trying to find comparator replacement to unobtanium LMH7322 (LMH7324 also not available from the sources i usually buy things from), not an easy task..
--- End quote ---
I doubt you will find anything compatible and cheaper. They are available from e.g. Mouser and Digikey, aren't they?
Make sure to look not only at the input specs (levels & speed), but also at the differential outputs. You need RSPECL (Reduced Swing Positive Emitter Coupled Logic) outputs to make your scope happy.
Mechatrommer:
--- Quote from: ebastler on December 02, 2023, 12:51:24 pm ---
--- Quote from: Mechatrommer on December 02, 2023, 12:46:28 pm ---just now trying to find comparator replacement to unobtanium LMH7322 (LMH7324 also not available from the sources i usually buy things from), not an easy task..
--- End quote ---
I doubt you will find anything compatible and cheaper. They are available from e.g. Mouser and Digikey, aren't they?
--- End quote ---
i'll try to find cheapest source i can get first, even from aliexpress 8pcs ADCMP576 alone will cost me $69, mouser and digikey will cost much more damage to my place guaranteed. 10pcs LT1715 is $37 though, but not look deeper on suitability. if no cheaper option, or if its not worth the effort to redesign, then i might just get the $75 probe from ebay, but then not sure what ic it is using. no prog delay spec no BW no nothing, so its shady.
--- Quote from: ebastler on December 02, 2023, 12:51:24 pm ---Make sure to look not only at the input specs (levels & speed), but also at the differential outputs. You need RSPECL (Reduced Swing Positive Emitter Coupled Logic) outputs to make your scope happy.
--- End quote ---
not sure about this yet, limited reading resources. but isnt LA input (comparator output) directly connected to DHO FPGA? ie just logic input 0 and 1? as long as within voltage limit range it should be ok, no?
ebastler:
--- Quote from: Mechatrommer on December 02, 2023, 01:05:00 pm ---if no cheaper option, or if its not worth the effort to redesign, then i might just get the $75 probe from ebay, but then not sure what ic it is using. no prog delay spec no BW no nothing, so its shady.
--- End quote ---
The low-cost probes do not use comparators with an adjustable threshold, but simpler LVDS drivers -- SN65LVDS1DBVR or similar multi-gate parts. You might be able to spot on the ebay photos what has actually been populated.
--- Quote ---not sure about this yet, limited reading resources. isnt LA input (comparator output) directly connected to DHO FPGA? ie just logic input 0 and 1? as long as within voltage limit range it should be ok, no?
--- End quote ---
The FPGA inputs are configured for LVDS (low-voltage differential signaling), and the comparator voltages are chosen such that the RSPECL outputs are compatible with that. You will need differential outputs on the comparator; they could be LVDS instead of RSPECL, I guess.
The LT1715 you mentioned does not have differential outputs, and its output voltage might damage the FPGA's LVDS inputs? LVDS logic levels are only 1.0V and 1.4V; not sure what the FPGA can tolerate as absolute maximum ratings.
Mechatrommer:
--- Quote from: ebastler on December 02, 2023, 01:40:11 pm ---The LT1715 you mentioned does not have differential outputs, and its output voltage might damage the FPGA's LVDS inputs? LVDS logic levels are only 1.0V and 1.4V; not sure what the FPGA can tolerate as absolute maximum ratings.
--- End quote ---
yes noted with concern, thanks for the info... while working on another section of dho, i got stucked since some parts havent arrived yet so i start doing reading on LA section, and i managed to pop something out of my fw hacked dho804 with help from diagram you provided earlier, without needing to flow solder the 2x DDR3L RAM in, so there's interesting hope. interestingly, sampling rate and memory depth not reduced so bad when this got activated as somebody else reported/portrayed much earlier. only halved and thats not too bad, its normal imho. 625MSps still can debug 300MHz 16ch logic, yes? ;D :-+
ps: i guess low cost probe for DHO800/900 and discussions should not be posted here right? otherwise police will tantrum? ;D i prefer to call "advisor" because advisor we can ignore, police if we ignore, we will go to jail, or got banned and cannot post in forum anymore. i sometime will become nonsense advisor myself :P
ebastler:
--- Quote from: Mechatrommer on December 02, 2023, 02:05:13 pm ---while working on another section of dho, i got stucked since some parts havent arrived yet so i start doing reading on LA section, and i managed to pop something out of my fw hacked dho804 with help from diagram you provided earlier, without needing to flow solder the 2x DDR3L RAM in, so there's interesting hope. interestingly, sampling rate and memory depth not reduced so bad when this got activated as somebody else reported/portrayed much earlier. only halved and thats not too bad, its normal imho. 625MSps still can debug 300MHz 16ch logic, yes? ;D :-+
--- End quote ---
Be careful when probing around and making connections across the 50-pin connector! There are definitely voltages there which the LVDS inputs won't like, including negative voltages.
The 625 MHz sampling rate for the LA is as expected, and I agree that it is adequate. A bit inconvenient maybe that it's such an odd number. The remaining 625 MHz for a single analog channel, or only 156 MHz when using 3 or 4 analog channels, are the disappointing part. (And the part which is not "normal" -- the analog sampling rate in MSOs is typically limited by the ADC, and does not get reduced when digital channels are activated.)
That AWG board looks promising! :) But yes, let's be good boys and move this scope-specific discussion to the DHO800 hacking thread.
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