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| A High-Performance Open Source Oscilloscope: development log & future ideas |
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| nctnico:
An update on the analog front-end. No white smoke yet. What I was already afraid of turned out to be the case. I basically started with the circuit I stopped working on over a decade ago (more or less the schematic I posted earlier). This circuit has seperate attenuator sections which get switched on/off using relais. I have come up with the following attenuation / gain table to get to a wide variety of attenuation ranges: There are 3 attenuation factors: 2.5, 10 and 200 and a 10x amplification stage on top of a standard 2x amplification (where it says 1 in the table there is no attenuation / amplification; Excel just works easier this way). The ADC's maximum input amplitude is 2Vpp (differential). Now to the board: I thought I had found some nice voltage controlled capacitors for NFC applications but these turned out to have a 30k Ohm DC resistance so useless in a high impedance circuit. So back to using varicaps (which I have used before). Using some low voltage high ratio varicaps I managed to get a decent voltage controlled adjustment range which seems to work nicely using a +/- 5V supply. I added these with some hacking. The biggest problem with the circuit is that the long traces have too much inductance and thus start to resonate at frequencies well over 50MHz causing dips and peaks in the frequency response. That was the part I already was afraid off and while measuring it dawned to me that I had originally designed (and probably tested) this circuit to work to 45MHz. The NanoVNA I bought recently served as a really nice tool to measure the frequency responses quickly. All in all I will need to rethink the input divider. I can still use the board to do more testing and use it to verify some modelling of the board by including trace inductance into the divider design. Also the anti-aliasing filters need to be tested (the large number of unpopulated 0402 components). I have included a relativile steep elliptic filter and a Bessel filter. |
| tom66:
Nice work. Unfortunately, I've not had enough time to look at the Jetson again. Also, EEVblog doesn't notify me about replies on this thread for some reason, I'll try to keep up to date. |
| tom66:
I think everyone here is owed an update as it has been a long while now. Unfortunately, I've come to the conclusion that realistically, I can't gather enough time to finish this project, with my career and other work taking up most of my free time. I am currently in a precarious living situation, looking to buy a home soon but in a market that has gone crazy due to COVID/work-from-home. So, I find myself working long hours and generally not having enough time or energy left to look at this, in order to be able to provide the down payment on a home. I am kicking myself for not doing this years ago, but that is FOMO and we don't do that here. Longer term, I do want to revisit it and give another look to the platform and the software, but it probably won't be for another year or so when things have settled down on my personal side. I have a lot of ideas for how to improve the platform. I am more than happy for the community (if interested) to continue this project; as noted previously, everything is now open source, and I can supply the hardware schematics and designs in CircuitMaker (you can find them by looking for 'Scopy_MVP_Platform', they should be public). But realistically this project requires several more man-years of effort, which I just cannot give it. In any case, my day job now mostly involves dealing with Zynq and UltraScale and it's really hard to find the time or energy to continue starting at Vivado after doing 10 hours of it every day. At my old job I was only doing basic microcontroller and analog circuit design so I felt I had a lot more 'bandwidth' available to do project work after a work day. Anyway, I appreciate all of the advice and comments on here and, maybe someday, there will be a good open-source scope available. But, sadly, I don't think I will be the one to deliver it - not just yet, at least. |
| 2N3055:
--- Quote from: tom66 on June 08, 2021, 08:31:48 pm ---I think everyone here is owed an update as it has been a long while now. Unfortunately, I've come to the conclusion that realistically, I can't gather enough time to finish this project, with my career and other work taking up most of my free time. I am currently in a precarious living situation, looking to buy a home soon but in a market that has gone crazy due to COVID/work-from-home. So, I find myself working long hours and generally not having enough time or energy left to look at this, in order to be able to provide the down payment on a home. I am kicking myself for not doing this years ago, but that is FOMO and we don't do that here. Longer term, I do want to revisit it and give another look to the platform and the software, but it probably won't be for another year or so when things have settled down on my personal side. I have a lot of ideas for how to improve the platform. I am more than happy for the community (if interested) to continue this project; as noted previously, everything is now open source, and I can supply the hardware schematics and designs in CircuitMaker (you can find them by looking for 'Scopy_MVP_Platform', they should be public). But realistically this project requires several more man-years of effort, which I just cannot give it. In any case, my day job now mostly involves dealing with Zynq and UltraScale and it's really hard to find the time or energy to continue starting at Vivado after doing 10 hours of it every day. At my old job I was only doing basic microcontroller and analog circuit design so I felt I had a lot more 'bandwidth' available to do project work after a work day. Anyway, I appreciate all of the advice and comments on here and, maybe someday, there will be a good open-source scope available. But, sadly, I don't think I will be the one to deliver it - not just yet, at least. --- End quote --- Tom, Thank you for letting us know, and I wish you a good luck finding and buying a new home... Life comes first... Take care, Sinisa |
| rhb:
FWIW I'd like to note that there is a 2nd prototype with a 7020 installed which I paid for which *really* should be in the hands of someone who wants to work on it. Like Tom, I just don't have the time. I had him keep it lest there be an accident with the other prototype. Tom asked me if I'd pick up the tab for the 2nd prototype unit which I did, but I was a bit skittish about the resources in the Zynq part Tom chose. So I paid to have a 7020 instead. It's got a *lot* more resources than the 7014S. Both of us would really like to see someone grab the ball and run with it. So if anyone is interested, contact one or the other of us. Tom and I have been using iPads, Facetime and MS Whiteboard to discuss technical stuff. I can't speak for Tom, but I can certainly make time for consulting on DSP if someone wants to work on this. There are some very cool features a la high end LeCroys I want to see implemented in a low end DSO. Have Fun! Reg |
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