Digital Oscilloscope

[nblfyb]

Hi, my name is Sean Browne. I was doing some research for my school's design project and I came across this site. We need some help with our project. We have to design a 10Mhz dual channel, digital oscilloscope with and input voltage rage of -12/+12 volts. The display should be the waveform and it's addition and subtraction. It should be displayed on a computer via the USB port. Other requirements are multi-level triggering and aliasing detection.

As of now, our group has been searching different A/D converters and USB boards, and decided to use an op-amp to step down the input voltage to the A/D converter. We would like some suggestions in going about a project like this and what type of A/D converters, USB boards and software would be good to use for this design.

I would like to thank you in advanced for any help we receive. You can email me at nblfyb2002@yahoo.com. I look forward to hearing from you.


Sean Browne

 

[Nigel Goodwin]

You don't need an opamp to 'step down', all you need is a simple potential divider - in the case of a scope you need to compensate it though by adding capacitors as well. What you may need though is a buffer amp after the attenuator, to match the attenuator to the A2D.

 

[gramo]

Many sound cards come with excellent 24Bit Analogue to digital converters, but they have low input impedance.

To use them as a "digital cro" you will need some freeware software, and a simple input buffer to increase the input impedance to around 1M ohm

Have a look on Google " free pc digital scope"

 

[Hero999]

The problem is sound cards are limited to 20kHz, even if they're capable of sampling at 192kHz which is a total waste of bandwidth anyway.

 

[nblfyb]

PC oscope

Thanks. So, after stepping down the input voltage, we are trying to determine a good A/D converter to use, preferably one that will connect to a USB board so we can connect to the computer to display the information. In some designs I've seen online, they use other components, such as, PIC controllers, amplifiers and I can't remember the others. I am confused as of what route to take for this design. Thanks.


Sean Browne

 

[evandude]

Take a look at the bitscope. I believe it started out as a build-it-yourself scope, and they made schematics and such available. It's now a commercial product but I believe the schematics for the old version are still available. At least you can get an idea of what's involved.

It sounds like you're hoping to hook an ADC to some USB board and just send all the data to the PC in real-time and do all the processing there. Bear in mind the kind of data rate you're dealing with here. If you want to build a 10MHz scope, you need to sample each channel at at LEAST twice that, so you're looking at a minimum of 20Ms/s per channel. If you're using 8-bit ADC's that's 320 Mbps, which is not all that far from the usb 2.0 limit of 480Mbps, and is likely much more than you could possibly achieve with some kind of commercial USB board... and would likely be far too challenging for a school project.

Normal digital scopes capture data intermittently to high-speed RAM, and the data can then be transferred to a PC (or displayed on a screen, or whatever) at a more reasonable speed. I believe the bitscope has an FPGA which handles the high-speed interface between ADC's and RAM, and a microcontroller for the lower-speed PC interface.

Starting from zero and learning to use FPGA's, microcontrollers, and high-speed ADC's and RAM, along with all the other design challenges, seems like a VERY tall order for a school project. Making an oscilloscope that works somewhere in the range of tens or hundreds of KHz might be reasonable, but 10MHz is a different story, and I find it surprising that any advisor would approve such a project...

 

[Nigel Goodwin]

'School' is perhaps a bit incorrect?, 'University' sounds more like it, and he's posting from a University address - digital scopes have often been a common University project.

 

[nblfyb]

PC oscope

Ok, thank you very much for the assistance. One company suggested one of their ADC combined with USB boards. Here is the link for it:

**broken link removed**

But, we are not sure of this board because of its high price. What do you think about it. Thank you.


Sean Browne

 

[Nigel Goodwin]

Ok, thank you very much for the assistance. One company suggested one of their ADC combined with USB boards. Here is the link for it:

**broken link removed**

But, we are not sure of this board because of its high price. What do you think about it. Thank you.

But how would buying a ready made device meet the requirements of your course?, it's really no different to just going out and buying a scope?.

 

[gramo]

he's posting from a University address

How do you know this?

 

[Nigel Goodwin]

How do you know this?

All IP's are logged by the forum software, his is a university address.

 

[gramo]

Ahh, tricksy

 

[gramo]

Gratz on 17,000 Posts Nigel!!

Thats an epic amount of support! How long have you been on this site for?

 

[Nigel Goodwin]

Gratz on 17,000 Posts Nigel!!

Never noticed?.

Thats an epic amount of support! How long have you been on this site for?

You know where it says you location? (at least where it SHOULD be filled in) it gives the joined date just above that.

 

[gramo]

Ah ha

lol, was that directed at my 'lack' of location info?

I'll fill it in one day

 

[gramo]

You should know it anyhow, as you can see all of out IP's

 

[Sceadwian]

That still irks me, very invasive. You should only look up an IP if you have a legal need to. Though I do understand the whole location bit when people are asking part sourcing questions or other location specific ones. If it's that big a problem simply require a country of origin entry when creating an acount.

 

[Nigel Goodwin]

That still irks me, very invasive. You should only look up an IP if you have a legal need to. Though I do understand the whole location bit when people are asking part sourcing questions or other location specific ones. If it's that big a problem simply require a country of origin entry when creating an acount.

Grow up! - this is the 21st century, NOT the 19th - everything you do on-line is logged all over the place. If you find that a problem I suggest you move to the middle of nowhere and become a hermit?.

The rare occasions I ever mention information from IP's is only when it's relevent - I read EVERY post on these forums, and only mention it to avoid wasting bandwidth and MY time (as well as everyone elses).

 

[Torben]

Grow up! - this is the 21st century, NOT the 19th - everything you do on-line is logged all over the place. If you find that a problem I suggest you move to the middle of nowhere and become a hermit?.

The rare occasions I ever mention information from IP's is only when it's relevent - I read EVERY post on these forums, and only mention it to avoid wasting bandwidth and MY time (as well as everyone elses).

Yes, I know I'm too young on this forum to pull much weight, but I have to go with Nigel on this. I know most people's phone numbers when they call me. I know most people's IP addresses when they email me. I administrate several sites, and I know from whence my accesses come. It's just there. It's nothing diabolical.


Torben

 

[Hero999]

If you really need to keep your identity secret then use a proxy server somewhere and make sure you have a pretty good privacy protection agreement with them.