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Author Topic: Using a scope
Digital-
Larry

Posts: 192
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Post Using a scope
on: February 6, 2013, 07:03
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Using a scope is very powerful for debugging circuits or simply understanding what is going on when you build something even if it does work correctly. However they are expensive and can be somewhat complicated to use. I was at Fry's yesterday, which is my local electronics store, and the cheapest one they had was an old school CRT model for a little under $400.

What I am using is an external pod which attaches to my laptop on USB and has two places to attach a 1x/10x probe so you can get dual traces.

This is the model I have. It was about $400 several years ago.

https://www.vellemanusa.com/products/view/?country=us&lang=enu&id=522377

Velleman also offers a small handheld model for about $200.

https://www.xump.com/science/Handheld-Scope-Velleman-HPS140I.cfm?SID=12&gclid=CI6vsJ_sobUCFWyCQgodCGIAbA

YouTube review:

Anyone have experience with any of these inexpensive handheld scopes for audio and FX work? Given the clock circuits in some of these BBD based FX might go up to a few hundred kHz, I'd say that a 1 MHz bandwidth would cover MOST analog FX work.

mwseniff

Posts: 149
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Post Re: Using a scope
on: February 11, 2013, 04:42
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I used the early Flukes and HPs which were OK but I am a lover of CRT scopes ( they also keep your grilled cheese sandwich warm). You can still find great deals on used CRT scopes at used electronic surplus stores and ham fests (amateur radio geek outs). I've also looked at some of the cheaper SS scopes the only problems I had were the input impedance could be too low but a 10:1 probe helps that. Audio techs usually spec 20MHz dual trace but IMHO a 50-100 MHz triple trace is best if the budget allows (2 inputs for stereo audio + a handheld probe for troubleshooting). You may well find the LCD scopes good enough for your purposes but I always found the cheaper ones to be less than satisfying for pro level work. For freezing a section of a waveform the LCD types are real winners, they are also good for triggering on events and capturing glitches. Keep in mind tho' that I have spent hours in front of an old o-scope with a grease pencil so I could mark the top and bottom of a intermittent transient peak before scopes got smarter and cheaper. I would look at one of the usb pc data acquisition interfaces and put it on an outdated PC on the bench plus you would have a PC on the bench for other uses. Not to mention that a little programming of the data acq interface and you could do long term monitoring of intermittent failures and logging of multiple voltage or current measurements. If there is a way to try one out and send it back that would be ideal. I wish I had a little more current knowledge but I've been away from it for 6+ years but I was keeping pretty close watch on them with an eye to deploying them for mobile on campus servicing. We ended up buying a few HP color LCD to pass around but I still wanted a scope in every tool box. We also setup a few PCs with data acq boards and preamps etc. for troubleshooting. The capture fcn on the digital HP scopes is a very useful feature that I wish I had about 35+ years ago on repairs I still wake up and think about in the middle of the night. The main place I really liked the LCD scope was when working around the big magnets at the chemistry dept. as you needed to be able tweak some RF trimmers for phase aligning the probe as one step in the overall probe setup routine. Not only did the LCD scope work in close proximity to very large magnets but it was small enough to place near the work area to see it and the alignment points simultaneously.

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