Nucleo & Discovery boards oscilloscope & AWG (Kickstarter) - Page 1
Forum section: electronics / general

author: hugeone
author_rank: Contributor
timestamp: June 26, 2016, 10:58:26 am
content: Hi Guys,I have just started my Kickstarter campaign.https://www.kickstarter.com/projects/1673888854/oscilloscope-and-awg-for-arduino-st-nucleo-and-disAny feedback appreciated

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: June 26, 2016, 06:41:02 pm
content: From your kickstarter page: "Bandwidth: 20MHz+"You may wish to amend that. If there is no appropriate bandwidth limiting of the inputs for a given sampling rate I would call it a design error.I could not find any mention of the copywrite licensing scheme(s) you are releasing it under. So I assume proprietary/closed for both hardware and software.

author: hugeone
author_rank: Contributor
timestamp: June 26, 2016, 10:13:21 pm
content: Yes you are right. It is actually much higher but I will have the actual figure when I receive the pcb-s from manufacturer. I use quite fast 250MHz front end op-amps.Thank you very much.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: June 26, 2016, 11:06:10 pm
content: Quote from: hugeone on June 26, 2016, 10:13:21 pmI don't think you understood my objection, too subtle perhaps.You may wish to study nyquist and his sampling theorem. I will let the Oscilloscope gurus here explain it as they can do a better job.

author: hugeone
author_rank: Contributor
timestamp: June 26, 2016, 11:22:50 pm
content: Bandwidth is actually the front end analog parameter. It does not have anything to do with the sampling and Nyquist . It is even more complicated as the frequency response of entire circuit should be as flat as possible. Unfortunately there is no way to simulate it with enough accuracy so I have to wait for my PCB-s to come.It is quite obvious that I need at least 8 - 10 samples/period to reconstruct the signal.

author: JPortici
author_rank: Super Contributor
timestamp: June 27, 2016, 01:54:42 pm
content: i believe he's asking why the front end has +20MHz bandwidth if it will be used in a series of systems with an ADC that has a max sample rate of 10 MS/s, how will you prevent the massive aliasing, because i think this is targeted to people with little money for a scope but that will have to look at 5-10 MHz signals or more

author: hugeone
author_rank: Contributor
timestamp: June 27, 2016, 03:39:51 pm
content: Bandwidth - I believe that more is better, as the analog part has better frequency response. It should be actually much more, but I have not measured it yet. There is no way of preventing the aliasing. But I understand what you mean, and I will add the link to the page explaining what the analog bandwidth is.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 28, 2016, 04:22:41 pm
content: Quote from: hugeone on June 27, 2016, 03:39:51 pmOf course there is, you lowpass the signal so there's little-to-no contribution from frequencies above nyquist. That's why "100 MHz" scopes typically use 1 GS/s sample rates...it's not because they can't get the analog bandwidth above 100 MHz, it's because they SHOULDN'T use an analog bandwidth above 100 MHz when their sample rate is only 1 GS/s. Similarly, if you only have a sample rate of 10 MS/s, you should be designing the front end for <1 MHz bandwidth to prevent aliasing.The attenuation from the analog filter as you near the rated bandwidth is what lets you know you're approaching the scope's limits. Without a filter to prevent aliasing, how could you ever trust what you're seeing on the screen? I would much rather have higher frequencies be attenuated than have them masquerade as lower frequency signals with no way to tell the difference.

author: JPortici
author_rank: Super Contributor
timestamp: June 28, 2016, 05:56:58 pm
content: Also no point in having a rise time in the order of a couple of ns if you're sampling at less than 10MS/s. in real time sampling each sample will be 100ns apart (in this 10MS/s example. in the usual stm32f1,f3 where you have 2.4 MS/s ADC so 416 ns between each samples (or if you interleave the three ADCs into 7.2 MS/s, 138 ns)Maybe you are using ETS or some other method to "cheat" into sampling higher frequency repetitive signals? great! but in my opinion your sample rate is still too low. 10 MHz input for a 10MS/s ADC should be the most for a DSO

author: ez24
author_rank: Super Contributor
timestamp: June 28, 2016, 06:25:13 pm
content: HiCan you discuss shipping to the US. Is there any chance you could compare your scope with other arduino scopes?Is the software in the video the real thing or a simulation?thanks

author: hugeone
author_rank: Contributor
timestamp: June 29, 2016, 08:13:00 am
content: Quote from: ez24 on June 28, 2016, 06:25:13 pmThis is the real thing.It is difficult to compare to Arduino scopes as ATmega micros have very limited ADC's.Quote from: JPortici on June 28, 2016, 05:56:58 pmI will take your point into consideration. Probably on one channel I will implement switchable LPF to limit it. 10 But the aliasing is not the only problem. Any not sine signals require higher bandwidth (more harmonics) to be reproduced in their original form.