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Old 27th July 2010, 06:40 PM   #1
Cassiel is online now Cassiel  Libya
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Default Looking for oscilloscope recommendations.

A friend of mine needs a scope that can capture 0.1-2Hz signals with accuracy. His budget is tight, so the cheaper the better. Any recommendations that you may have would be greatly appreciated.
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Old 27th July 2010, 07:54 PM   #2
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What about using a sound card, with high resolution (24bit) and high sampling rate (192KHz)? Probably the cheaper you can find is the E-MU 0202.

About the software, there are many pc based oscilloscope ones, ranging from virtins (Virtins Technology: Turn a PC into Virtual Instrument - Home) to picoscope (which requires his own hardware PicoScope PC Oscilloscope and Data Acquisition Products from Pico Technology) to many others. Try googling "pc oscilloscope".
This one is interesting Visual Analyser 2011

But if he needs also higher frequencies, a sound card based oscilloscope won't be enough though
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Old 27th July 2010, 08:00 PM   #3
SY is offline SY  United States
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Most of them use cap coupling, so 0.1-2 Hz is going to be a bit of a reach.
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Old 27th July 2010, 08:12 PM   #4
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so you have just to remove those caps
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Old 27th July 2010, 08:21 PM   #5
jcx is online now jcx  United States
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if you know more about the signal properties and can accept PC display you may be able to use a ~ US$100 DAQ module

USB 12-Bit Multifunction Solutions from Measurement Computing

there are also standalone USB data loggers for even less
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Old 27th July 2010, 08:47 PM   #6
Cassiel is online now Cassiel  Libya
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It's for testing a subsonic network at the input of a tube amp. Beats me. Yes, he has a PC.
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Old 27th July 2010, 09:37 PM   #7
jcx is online now jcx  United States
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Quote:
Originally Posted by kingbowser View Post
so you have just to remove those caps
unfortunantly this won't often work - soundcard ADC usually are single supply and have DC input bias requirement

also the ADC are mostly delta-sigma types with high-pass built in to their hardware digital filters

Last edited by jcx; 27th July 2010 at 10:02 PM.
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Old 27th July 2010, 09:53 PM   #8
kevinkr is offline kevinkr  United States
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It's for testing a subsonic network at the input of a tube amp. Beats me. Yes, he has a PC.
I would think that demonstrating that the filter is at least -3dB at 15Hz and is dropping monotonically below that would be sufficient. Measuring lower than 10Hz with anything other than a DSO is going to be an exercise in frustration.. (Good data acquisition hardware to do this probably is out of budget, but who knows..) Truthfully a good true RMS multimeter may be as useful at these frequencies doing static measurements provided that it has usable response below 10Hz.

My PC based FFT set up is useless somewhat below 20Hz.. (Both comments in post #7 are true IMLE)
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Last edited by kevinkr; 27th July 2010 at 10:05 PM.
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Old 27th July 2010, 10:42 PM   #9
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Any decent analog scope with a AC/DC input switch can show right down to DC - if switched to DC. A real nasty cheapo may have internal AC coupling, so would be useless.

You can buy a good one new for maybe $500, or get a used HP or TEK scope for maybe around $100 that originally cost $10,000. One with a longer persistance screen would help seeing very LF signals.

Or spend maybe $1000 and get a low priced Chinese made Digital scope - that will do the job perfectly. There's a company that OEM for Agilent (HP), dunno the name.

Fitzing with sound cards etc will just become a hassle, IMO, at the very least cost a lot of time.

Regards, Allen
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Old 27th July 2010, 11:43 PM   #10
chrish is offline chrish  Australia
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If looking at cheap DSOs, I recently purchased a Rigol DS1052E 50mHz model. It is cheaper than the 100mHz model ($400 vs $600), but is identical. All that is needed is a software hack to convert it to the 100mHz model, see here EEVblog #77 – Rigol DS1052E DS1102E Oscilloscope Hack Update @ EEVblog – Electronics Engineering Video Blog Podcast
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