Oscilloscope needed

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cosmicray
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Oscilloscope needed

Post by cosmicray » Wed Dec 17, 2014 7:59 am

Hi, I think it's time I invest in an oscilloscope. Picking one is turning into a devil of a choice.

From what I can tell, there are two basic styles, one is a conventional desktop model with integrated screen (like Sparkfun sells), the other is a USB style, which uses the PC's screen. It is possible that I will want to use this where I do not have access to AC power. The GA1102CAL, which looks like a nice product, requires AC power. That adds to the bucket list should I ever want to operate it portable (inverter, 12V source, etc). The USB powered scope (Hantek, et al) draws power from the USB bus. So plugging it into the USB on a laptop seems like a way to do portable operations.

The two concerns I have are the current draw from USB (not documented that I can find) and the notation in the Hantek documents that the PC should be grounded (presumably to limit noise from a floating power source). Does anyone have any thoughts on either of these concerns ?
First learned EE at the juncture of vacuum tubes and solid state, Still learning.

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Ross Robotics
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Re: Oscilloscope needed

Post by Ross Robotics » Wed Dec 17, 2014 9:22 am

If you are doing Arduino stuff, look into a logic analyzer. Much more useful. Well, most computers can only source up to 1A on the USB bus, so you can count on any USB device to be under that.

If you do more discrete IC projects, than a O-scope would be more useful. I would highly recommend getting a name brand unit, like a Tektronix, Onan, etc.. And make sure it's calibrated. You can find a good Tektronix 100MHz on Ebay pretty cheap.

On the ground question, most homes that were built or remodeled in the last 20 years have been inspected. So this means that every outlet should have an earth ground. So you should be good there. Another thing to note is if your project is running off AC, then you need to have the O-scope on a different circuit than your project to get away from ground loops.

A great place to start is EEVBlog. Lots of good info about O-scopes and Analyzers. I can't find the O-scope selection video though..
https://www.youtube.com/user/EEVblog/featured
http://www.eevblog.com/
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Valen
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Re: Oscilloscope needed

Post by Valen » Wed Dec 17, 2014 10:04 am

Beware of Dave's USB scope rants. He did make a favourable one last week though.

I have a hantek usb scope (DSO 2090) and it needs to be powered from 2 usb ports. It starts with just 1 plugged in but may not work correctly. So take that into account.

cosmicray
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Re: Oscilloscope needed

Post by cosmicray » Wed Dec 17, 2014 12:59 pm

Valen wrote:Beware of Dave's USB scope rants. He did make a favourable one last week though.

I have a hantek usb scope (DSO 2090) and it needs to be powered from 2 usb ports. It starts with just 1 plugged in but may not work correctly. So take that into account.
That implies that it's drawing more than 500 mA, which is what I was concerned about (seeing as how Hantek has not provided any real numbers in the spec sheets). To use one properly, I would need a special USB cable that sends data lines to the laptop, and gets power from an external source (else it would be draining the laptop battery).

Time to look at choices in the conventional scope market. Would be nice if one of them could be powered directly from 12V.
First learned EE at the juncture of vacuum tubes and solid state, Still learning.

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Re: Oscilloscope needed

Post by Valen » Wed Dec 17, 2014 3:25 pm

cosmicray wrote:...
That implies that it's drawing more than 500 mA, which is what I was concerned about (seeing as how Hantek has not provided any real numbers in the spec sheets). To use one properly, I would need a special USB cable that sends data lines to the laptop, and gets power from an external source (else it would be draining the laptop battery).
It was included when I bought it.

Something like this:

Image

[EDIT] Whoops! Being blind again:
... and gets power from an external source (else it would be draining the laptop battery)

cosmicray
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Re: Oscilloscope needed

Post by cosmicray » Wed Dec 17, 2014 3:53 pm

One picture is worth a thousand mili-amps. :clap:

Thank you.
First learned EE at the juncture of vacuum tubes and solid state, Still learning.

cosmicray
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Re: Oscilloscope needed

Post by cosmicray » Wed Dec 17, 2014 8:02 pm

It also just occurred to me, that building my own USB cable, with a Pololu D24V10F5 regulator board, would give me the 5V @ 1A, without impacting the laptop battery (assuming I have a nice 12-13V source handy). Hmmm.
First learned EE at the juncture of vacuum tubes and solid state, Still learning.

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Ross Robotics
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Re: Oscilloscope needed

Post by Ross Robotics » Wed Dec 17, 2014 8:47 pm

I have one of those 10,000mAh portable battery pack that has a USB port that can source 1A and has a 12V source (can't remember the rating on that).
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cosmicray
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Re: Oscilloscope needed

Post by cosmicray » Thu Dec 18, 2014 6:56 am

Yeah, I've got some 210,000 mAh deep cycle golf cart batteries to mess with. They mass a bit more than the unit you're speaking of, but they have more staying power. :D
First learned EE at the juncture of vacuum tubes and solid state, Still learning.

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Re: Oscilloscope needed

Post by Valen » Thu Dec 18, 2014 8:40 am

As you need to regulate it to 5 volt you do need to consider the ripple on it. As it is a measuring device you want as little of it on the 5 volt line, And take care that high frequncy switching components don't feed through. But those could be there with a computer-only connection aswel. Tldr: mind the filtering.

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Re: Oscilloscope needed

Post by stevech » Thu Dec 18, 2014 11:06 pm

My Hantek DS2090 (20MHz, $100 or so).. has a cable with 2 USB connectors; 2nd one can sum power from a different USB port. But I normally use just one and it's fine.
Bought direct from small seller in China.
Scope does well for 8MHz and lower signals. Need 3x or 4x signal freqs in bandwidth and sampling rate. But for 99% of what I do, it's fine.

Recently got a Saleae Logic 8. Great. 8 digital inputs, any can also show analog. With just a few channels enabled, the digital sampling rate gets to 50Msps and the analog bandwidth gets to a few MHz. Good value.

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Re: Oscilloscope needed

Post by Valen » Fri Dec 19, 2014 5:25 am

stevech wrote:My Hantek DS2090 (20MHz, $100 or so).. has a cable with 2 USB connectors; 2nd one can sum power from a different USB port. But I normally use just one and it's fine.
Bought direct from small seller in China.
Scope does well for 8MHz and lower signals. Need 3x or 4x signal freqs in bandwidth and sampling rate. But for 99% of what I do, it's fine.
Have you also noticed that when a channel is set to ground and the trace is aligned to the vertical center line it is spot on it. But then you offset it vertically higher or below it the trace moves slightly away from the marker. As if there is some scaling issue in sotware, or maybe even hardware.

cosmicray
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Re: Oscilloscope needed

Post by cosmicray » Fri Dec 19, 2014 6:50 am

stevech wrote:My Hantek DS2090 (20MHz, $100 or so).. has a cable with 2 USB connectors; 2nd one can sum power from a different USB port. But I normally use just one and it's fine.
Bought direct from small seller in China.
Scope does well for 8MHz and lower signals. Need 3x or 4x signal freqs in bandwidth and sampling rate. But for 99% of what I do, it's fine.

Recently got a Saleae Logic 8. Great. 8 digital inputs, any can also show analog. With just a few channels enabled, the digital sampling rate gets to 50Msps and the analog bandwidth gets to a few MHz. Good value.
Last night I saw a set of specs (for the Hantek USB powered Logic Analyzer), that mentioned power consumption.

Voltage Range - 4.5V~5.5V
Power - Max. 3.5W

That suggests a maximum current draw of 700 mA (at max). I can see where one 500 mA USB port might work sometimes, but to hit maximum you would need two. The sales page and the DSO2090 manual, do not mention max power.
First learned EE at the juncture of vacuum tubes and solid state, Still learning.

stevech
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Re: Oscilloscope needed

Post by stevech » Sat Dec 20, 2014 8:25 pm

I connected my DS2090 'scope to a USB "Power Gauge" from Adafruit, to a USB 2 port on the front panel of my desktop PC. That's got an ASUS motherboard.
http://www.adafruit.com/products/1549

It shows current flow via serial port messages and by lighting LEDs for a coarse reading.
The DS2090 caused 3 of 5 LEDs to light.
The serial port output said:
V: 4.1 I: 646 mA Watts: 2.6
V: 4.9 I: 596 mA Watts: 2.9
V: 4.9 I: 648 mA Watts: 3.2
V: 4.9 I: 648 mA Watts: 3.2
V: 4.9 I: 648 mA Watts: 3.2
V: 4.9 I: 654 mA Watts: 3.2
V: 4.9 I: 644 mA Watts: 3.2
V: 4.9 I: 628 mA Watts: 3.1
V: 4.9 I: 630 mA Watts: 3.1
V: 4.9 I: 652 mA Watts: 3.2
V: 4.9 I: 648 mA Watts: 3.2
Using port on PC case.
Using a USB2 hub with other loads on it too, the voltage fell to 4.1 from the hub. Not too good. But that hub can be externally powered.

I also have a powered USB2 and USB3 hub - 2A power. Haven't tried that. I did plug the scope into a USB2 hub, unpowered, and it worked OK.
My computer seems to be OK with providing more than 500mA which is the minimum the USB spec requires, per port. As you know, the goodness of the USB hubs varies among different products. This is the one I use most, due to its switches; It has a 5V power-in port option - very handy
http://www.ebay.com/itm/7-Port-USB-3-0- ... 3a9e142088

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