EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: firewalker on October 14, 2011, 12:08:03 pm
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Someone asked me today what is the point of single-shot trigger in analog oscilloscopes (he didn't knew about oscilloscope cameras e.t.c.). Bla bla bla... Is there a digital storage for analog oscilloscopes? Like an add-on between the bnc connectors of the probe and the input.
Not something "crazy", just for sigle-shot events from a PSU etc.
(http://i.imgur.com/84hST.png)
Alexander.
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That would basically be a complete DSO, except the output would have to be converted to X,Y,Z instead of LCD. It would need amplification, attenuation, triggering and sampling. The LCD is not exactly the most expensive or complex part in a modern DSO. Getting a crappy low-bandwidth/voltage DSO would probably make more sense.
Analog storage was the old way of doing it, they used a special CRT that would retain the charge from the trace for a certain amount of time. This technique is inferior to a DSO, though, and completely obsolete, as opposed no normal analog scopes.
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I think Elektor published a circuit that did that back in the 80ies. That was a proper TTL grave though with just a few bytes (bits?) of sampling memory and almost certainly much worse than any of the cheap toy DSO's of today.
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Speaking for today, yes it wouldn't worth it. But analog oscilloscopes was the way to go several years ago.
Alexander.
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There's also different approach (http://hackaday.com/2011/03/16/adding-digital-storage-to-an-analog-scope/) to this topic.
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As I do not own a DSO this is the way I do it, today with digital cameras it is easier than in the days of Polaroid film but it is still a bit annoying ::).
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Triggering it within milliseconds to record a single shot trace might be tricky with cheap cameras, though.
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Triggering it within milliseconds to record a single shot trace might be tricky with cheap cameras, though.
It's actually not that difficult. All you have to do is to set the camera to a longer exposure time.
How to get nice pictures off analog scopes:
http://amplifier.cd/Technische_Berichte/Photographie_Oszilloskop/Foto_Halterung.html (http://amplifier.cd/Technische_Berichte/Photographie_Oszilloskop/Foto_Halterung.html)
There's also different approach (http://hackaday.com/2011/03/16/adding-digital-storage-to-an-analog-scope/) to this topic.
And yes that is the right and probably most practical approach to this problem.
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Long exposure works as long as ambient light levels are low or the hood is light tight. It also requires the trigger to occur within a few seconds of triggering the camera, i.e. it should not be a rare event.
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Is there a digital storage for analog oscilloscopes? Like an add-on between the bnc connectors of the probe and the input.
http://www.ebay.co.uk/itm/THURLBY-DSA524-DIGITAL-STORAGE-ADAPTOR-CABLES-INST-/380376033983?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item58902daabf (http://www.ebay.co.uk/itm/THURLBY-DSA524-DIGITAL-STORAGE-ADAPTOR-CABLES-INST-/380376033983?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item58902daabf)
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Yes, there have been a few magazine projects along these longs before PC based DSO adapters came along.
Dave.
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It's possible to do that with a CCD used as an analog shift register. If you're going to bother converting to digital and storing it, you might as well just stream it to a PC. There's little point in using an old fashioned boob tube nowadays...
An interesting hack would be to hack an old hard drive to act as an analog circular buffer. Just secure the heads in one position (easiest way is to apply a current to the linear motor), then have it record until a programmable time after a trigger, in which case it switches into playback mode.
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Iwatsu is making a 1GHz analog oscilloscope using a CCD connected to a CRT, and then display the traces on a LCD.
Tequipment has it, currently on sale, only $28k! :o
http://www.tequipment.net/IwatsuTS-81000.html (http://www.tequipment.net/IwatsuTS-81000.html)