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Z80
Joined: 20 Feb 2004
Posts: 96
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 10 Aug 2009 14:54 usb oscilloscope |
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Hi everybody
I've used my PC's sound card as a very basic oscilloscope for a while now but since I switched to a laptop which only has a mic input (very high sensitivity and can't be relied upon because of internal filters) I decided that I need an USB oscilloscope. Plus I'd like to upgrade the bandwidth. I searched on the net for commercial products but wasn't satisfied with the price/performance ratio, the only affordable products have a very narrow usable bandwidth. I'm currently on the reasearch for the feasibility of the project.
What I have in mind is (the bold requirements are not changable):
- use USB interface for portability
- no FPGA/CPLD (I don't have/afford a dev board and also have no usable knowledge about them)
- use a FT232R chip for USB to serial conversion
- price kept to a minimum
I'm aware of an older thread here about a PC DSO but it uses FPGA and is too complex for my hobby needs. Maybe oscilloscope is an improper name, what I have in mind is more of a voltmeter/digitizer with a PC interface. Basically a simple system consisting of a DAC connected by means of a MCU or wired logic (if possible) to the USB chip, which streams sampled data to the PC. Let's leave the details concerning the analog frontend for later.
My questions for now are:
- which is the max achievable sample rate I can squeeze out of a system like this?
- how difficult is it to handle USB software-wise?
- is a MCU mandatory for the control of the FT232R of can I get away with wired logic?
I'm not leaving out the option of buying a commercial product completely if the project proves to be unfeasible.
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wp100
Joined: 15 May 2009
Posts: 324
Helped: 45
Location: England
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10 Aug 2009 15:56 usb oscilloscope cheap |
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Hi,
Couple of things might be of interest - both the Elektor and EveryDay Practical Electronics magazines did a PC scope in 2007.
There are some details still on the web about them, athough the cost of building one might be more than buying something ready made or a decent second hand tube one.
For something much more simple - how about the Logic Analyzer Tool that is part of a Microchip Pickit2 programmer - see pfd for details - it also runs from the simple Diy Picikt2 versions as detailed in the Micro forum of this site.
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Z80
Joined: 20 Feb 2004
Posts: 96
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10 Aug 2009 16:58 usb oscilloscope kit |
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Hi wp100
Initially I considered buying an used Tek scope, but it's not portable and it's big and heavy. I really do need it to be portable from time to time.
I'll take a look at your suggestions, although an analog scope would be more suitable for my needs. But maybe a logic analyzer can be used for low bandwidth (in the 100's of khz range) analog measurements?
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wp100
Joined: 15 May 2009
Posts: 324
Helped: 45
Location: England
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10 Aug 2009 18:27 simple oscilloscope |
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Hi,
Those Pickit Logic Analyzers are strickly TTL digital.
Seems like the cheapest ready made unit to do what you want are about GB £150, if you want cheaper you might find something better on Ebay, but if its a good quality instument you want I would think buying direct from the makers/ main distrubutor is a better bet.
I bought a 60 meg dual beam Hameg scope 20 years ago for work use - its still going strong today - yes its heavy and bulky but you will have spend a lot on a modern PC scope to match its abilities.
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Z80
Joined: 20 Feb 2004
Posts: 96
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11 Aug 2009 20:15 oscilloscope simple |
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| wp100 wrote: |
Hi,
Those Pickit Logic Analyzers are strickly TTL digital.
Seems like the cheapest ready made unit to do what you want are about GB £150, if you want cheaper you might find something better on Ebay, but if its a good quality instument you want I would think buying direct from the makers/ main distrubutor is a better bet.
I bought a 60 meg dual beam Hameg scope 20 years ago for work use - its still going strong today - yes its heavy and bulky but you will have spend a lot on a modern PC scope to match its abilities. |
Buying an old CRT scope was among the (very early) options too, but since I don't need that wide a bandwidth... portability weighs a greater amount in my balance 
I found the Elektor issue that shows the USB data acquisition board (it's November 2007) and read the article. It doesn't say anything about the sample rate, but the 18F4550 datasheet states a minimum acquistion time of 2.45us which should be acceptable. I don't have a clue whether the SW supports that transfer rate. My initial idea (FT chip coupled to a ADC) promises a theoretically higher transfer rate... I'll have to study some more.
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11 Aug 2009 20:15 Ads |
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eltonjohn
Joined: 22 Feb 2002
Posts: 1751
Helped: 28
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11 Aug 2009 20:53 simple led oscilloscope |
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| Hi .. is nice to try to solve problems the easy way .I mean the cheapest way .A good scope is a MUST have . I recently bought one in ebay .I paid only $100 for a tekteronics 4 channel 100 Mhz just the price of the probes was more ! It was in mint condition and i even got all the manual .I saw there plenty of good opportunities for little money.Maybe you don't live in the US .But i think even with shipping included still a good option !.
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wp100
Joined: 15 May 2009
Posts: 324
Helped: 45
Location: England
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11 Aug 2009 21:02 ebay usb oscilloscope low cost |
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Hi Z80,
That USB Acquisition card is just that, an input data card - its nothing to do with a scope as such.
It was in the January 2007 that Elektor did their Uscope but having a look around think it didn't take off.
Also seems the chips uses in the EPE PC scope are no longer available either.
However did see this link which might be of interest, otherwise I think your are in to buying a ready made unit
http://www.seeedstudio.com/depot/digital-storage-oscilloscope-diy-kit-65288with-panels-p-166.html
See the other pages of this site for built units
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Z80
Joined: 20 Feb 2004
Posts: 96
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12 Aug 2009 17:26 quality of the usb oscilloscope |
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100$ for a 100MHz Tek puts my portability demand to question (I know, I don't change my mind easily )
But $33 for a 2Msamples/s kit is a definite WOW! I'm well past the age when soldering on a test board for a whole weekend used to sound like fun, so... :d And... $33 for the thing... did I already say WOW? Thanks a lot for that link. And eltonjohn, thank you too, I'll keep an eye on eBay too.
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eltonjohn
Joined: 22 Feb 2002
Posts: 1751
Helped: 28
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12 Aug 2009 18:47 sampling oscilloscope diy |
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The scope i bought was a tek 2246 digital readouts .Thanks to wp100 i dind't know that web site .The have great break boards and the scope is kind a nice too
cheap enough to incorporate it in some project
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Z80
Joined: 20 Feb 2004
Posts: 96
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12 Aug 2009 19:36 good quality usb oscilloscope |
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Glad to be of any help (even if unintentionally).
We use analog entry-level Tek scopes @work (don't know the exact type but I gather they're ~$3k new) and a team mate of mine told me they have a 200mV thermal drift. Thing is we (I) use them as digital scopes and we don't care about that, that's because some purchasing moron decided it's better to use crappy analog scopes for digital measurements instead of dedicated logic analyzers. And the analog guys can't use them obviously, which led to the purchasing of some LeCroy midrange scopes. Excuse my rant
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