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| New bench scope - Fnirsi 1014D, 7", 1GSa/s |
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| pcprogrammer:
Top. I will take a look to see what you have been up to :) About the relays, if they had only looked a bit beyond the length of their nose and used a high speed 4051 analog multiplexer it would have been easy to have more ranges then they have now. The 3 control lines for the relays are unfortunately limited in the FPGA to the allowed range it has now, instead of having the limit in software, otherwise it would have been easier to make the change. |
| donwulff:
I should have a look at that multiplexer, though the idea here is just to use the SSR to bypass the front resistor, which according to simulations is filtering the bandwidth... Because of that the on-resistance of the optoisolated SSR relay is pretty crucial, in fact if FNIRSI/whoever didn't account for it correctly, the one bypassing the AC coupling capacitor could be limiting the bandwidth further than they meant. (Also, we have to use optoisolated one there, because it's on the high-voltage size of the front-end). Once again though I'm aware that's not magic, for one thing that will cause higher frequencies to alias into lower ones due to the sample rate, however I want to test oveclocking the FPGA/ADC as well as potential for just getting phase of (known) higher frequency signals. That MAY require switching the OpAmp into the Texas Instruments one, with faster slew rate, and yeah that component's small too... In the pic the SSR is placed with legs right around the resistor it's supposed to bypass... which I should note, is really small, and I'm not at all confident about successfully soldering that. Another possibility would be placing the SSR at the corner with lots of empty space, but that would mean longer leads with associated noise. I'm not at all sure if placing the component on top of the others is better, but at least the SSR shouldn't cause much noise. If it works, it can be driven by the "special IC" pin, eventually. It seems the minimum sensitivity of the analog front-end is driven by the standard 1M resistor in the highest sensitivity configuration, so I'm not sure it's possible to push that further with sensible changes. There's been a mention of second op-amp stage somewhere. Note on the bench-top 1014D a separate analog switch for turning on extra circuits isn't entirely out of question, could be pretty indistinguishable from the standard user interface. However completely re-doing the analog front-end is just silly, and not something I particularly understand. Also the 1014D firmware doesn't do much "useful" right now, I just setup the cock gen & UART and hooked up some of the main buttons I'm experimenting with, barely clobbered up. Trigger Mode currently disabled in the code because it hangs, time-div stops working when moved too far either direction have to figure what's up with that. At least I can select trigger channel, auto-set the settings and switch time-scale to 200Msa/s|500ns/div and get some readings. 4051 multiplexer, data-sheet says it has 125 ohm ON-resistance. Of course, depends where it's used, if you have 1M+ resistor in front might not matter that much. It also seems to have no voltage isolation spec, just ESD. I'm not sure how important it is after the big resistors, but the analog relays are still 220VDC signal/1800VAC isolation, would need separate opto-isolators to be safe and maybe replace frequently. At any case the Chinese are pro's at minimizing components, you can be sure they don't plan for end-user upgrades. Was interesting seeing spot for one unplaced component on the analog front-end though, I wonder what that's for. In any case we're limited by the ADC's, I'm wondering if one could use both ADC's on single signal. FPGA's I've worked with had configurable output delays on signals, so even if there aren't free PLL resources, I'm wondering if it would be theoretically possible. Little point doing highly involved one-off customizations nobody else is likely to use though. Maintaining high-voltage separation is actually PITA with any modifications to the circuit. I wonder how much isolation the actual chip case offers. Placing the chip on top of others will also bring it closer to the tin-can cover which is connected to ground, and placing it to the empty corner would need passing long leads around the other components. The position displayed might be best spot due to that as well, but the clearances are going to suffer no matter what. I should've probably looked at the Hantek schematics earlier, though I don't think there's anything that would be useful with the analog front-end already in place in the FNIRSI. I guess https://www.ti.com/product/LMH6702/part-details/LMH6702MFX/NOPB is equivalent of what they're using as buffer OpAmp, so could've looked at that instead (Although DigiKey doesn't have them, AliExpress could send some Chinese clone?). And a differential OpAmp possibly with some gain after that? Can't use that on 1014D of course. Ah, and so much for attempting to get something else done, hah. |
| pcprogrammer:
:-DD I did not read your first post correctly. :-DD Thought you where on about the big relays and did not notice the extra component you put in :palm: I'm no expert on analog design at all, but the idea I had at some point was to just cut out the whole front end by slicing the traces to the ADC's and design a small circuit board with a new front end, but it is probably quite a bit of work to get it right and also not an easy setup for others to put in their scopes. Also things might get expensive and buying something better comes in reach quickly. To me it feels best to just tinker with the software and maybe the FPGA to learn and play. |
| Moley:
Hi all, Sorry if this isn't the right place to post - just looking for purchasing advice. I'm looking for an upgrade from my multimeter for audio frequency analysis. This scope has become quite cheap in Australia, so I thought I'd pick one up. I've considered similar Hantek models (quite a bit more expensive here), plus all the regular flagships (a LOT more expensive here) - from reading through this thread, I'm excited about the modification possibilities, and also convinced the major drawbacks won't have a significant impact on audible frequencies. At AU$264 (currently US$181.50, 167 Euro), I just wanted to check this would fit the bill for basic audio circuit analysis. Any advice would be greatly appreciated. Cheers, Moley |
| pcprogrammer:
Hi Moley, welcome to the forum. It depends on what information about your signals you want the scope to display. When it is just measuring on audio circuits to see if they come through as expected it could do the job, but keep in mind that the input sensitivity is not that high. 100mV per division with a 1x probe. (The 50mV per division is software zoom). About modification possibilities it also depends what you are after. Both hardware and software wise there is room for improvement. The 1013D version (The one without the knobs) has working open source firmware for it and might be cheaper. (See this thread) Hardware is much the same. |
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