Oscilloscope modules

[gusmanb]

I'm starting to get components to dessign the oscilloscope modules. The idea here is to have one or two ADC boards that can be triggered by a voltage level or a digital trigger.

For the digital trigger as we have 24 digital IO's available and the ADC's need 8 input channels for data and one clock signal I think we could have a digital trigger of up to 7 channels, or of course use a second analyzer and use the external trigger.

I have ordered a couple of ad9283 ADCs that can sample 8 bit at 100Msps, so it will give a good resolution with not an excessive price.

For the analog side of the device any help is welcome, I'm more a software/digital electronics guy than analog so any consideration, advice or help will be appreciated.

[phantomkingx]

Have you considered using the onboard pico ADCs which would provide 3 analog channels? I understand they are limited to 500kS/s but that may be quite useful for many applications. Although still not trivial the advantage would be just a firmware/software change to implement and it wouldn't use up any other channels.

Great work btw, just came across this project and see myself using the analyzer in the future.

[gusmanb]

Hi Simon!

Yes, that's something that I already have considered. It would be only useful for low frequency applications, with 500Ksps the maximum frequency that you would be sampling is 125Khz, and not in a very good fashion, only 4 samples per cycle will give you just an idea of the waveform, it would start to be useful at 60Khz~ and still I would not consider it "good".

In any case, I studied the possibility, at least for audio and low-speed I2C would be good enough but the Pico has a flaw in the ADCs which makes them useless for precise aplications, there are four concrete values that make the result to suddenly peak, you can check it on the RP2040 datasheet, check errata RP2040-E11, so I discarded totally the idea.

Anyway, I already have received two AD9283-100 IC's and a iCE40-ADC module, the AD9283-100 should be the ideal solution but will need a bit more tinkering by the user as it will need the assembling of the board, but the iCE40-ADC module is a pre-made solution that should work only by connecting 10 wires between the analyzer and the board. The best is that the firmware for both cases should be the same, so I think that having these two options available will be the best solution and will give an effective frequency of 25Mhz, which is something really useful.

Cheers!

[danielh186]

Do you know whether the flaw you are talking about got fixed in the RP2350?
Having 4 analog channels would be pretty cool. Even though I would not think of it as a replacement for a bench oscilloscope.

[phantomkingx]

Ah I see, always a fly in the ointment.