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Topic: budget USB oscilloscope (Read 5993 times) previous topic - next topic

Peter_n

Nov 26, 2014, 09:11 am Last Edit: Nov 26, 2014, 04:59 pm by Peter_n
Hi,
I was searching for something very specific:
- USB oscilloscope of about 100 dollars/euros.
- 2 analog channels capable to see ultrasonic waves up to 25kHz.
- 4 digital channels to watch a 4MHz SPI bus.
- Software should also run in linux.
- I prefer that the oscillocope is a shield for the Arduino Due.
- Some protection at the inputs, not just Arduino Due inputs.
- I want to buy it now, I don't want to wait for a KickStarter project.

If someone knows an USB oscilloscope that can do that, please tell me.
A 100 dollar oscilloscope can't be any good, but then I noticed a 41.90 dollar oscilloscope :
http://www.dx.com/p/usb-oscilloscope-and-logic-analyzer-93518
Can it be any good for 41.90 dollars ?


Peter_n

Thanks nilton61, but those are based on ATmega chips and the sampling rate of digital signals is too low. I need a little better.

rlogiacco

Please, do not send me personal messages containing forum related questions: I will not answer.

I share my discoveries and thoughts at http://rlogiacco.wordpress.com

polymorph

To view an analog 25kHz signal, you really need something that has a bandwidth much higher than that. And a sample rate a lot higher.

For a digital 4MHz signal, you really will find it useful to have an analog scope. A digital signal analyzer is great as long as the signal is clean, and you are only interested in looking at the data and timing. But you'll still need something with a capture rate something like 20x the maximum frequency of the clock. At least.

Think about it - a 4MHz signal has a 250ns period. But that is a 125ns time on or off. For a capture rate of 80MHz, that is only 10 samples per ton or toff, or 12.5ns granularity. But what if the duty cycle is not 50%? It gets worse, then.

If the signal isn't perfect, there may be ringing, or droop, spikes, etc. mucking up the signal. A digital analyzer can't show you what is going on.

But a 4MHz digital clock is a square wave, which is made up of the fundamental frequency and the odd harmonics in reducing power. The 9th harmonic is a realistic minimum to view a reasonably sharp square wave, ie, 10x analog bandwidth. More is better. But we need to take into account the timing issues discussed above, and duty cycles different than 50% mean different timing -and- higher harmonics necessary to reconstruct the signal.

Can you get away with the $42 DX.com USB scope? Probably 90% of the time, maybe more. But that smaller percentage will soak up an inordinate amount of your time troubleshooting a signal that you can't see clearly.

I've not seen a really good USB scope for $100. For $100, I think I'd look for a good used analog scope with at least a 100MHz bandwidth, dual channel. Or buy that $42 USB scope, and save up about $400 for a decent 1Gsps digital dual or quad trace scope. Don't waste your money on those little scopes that look like cell phones, they are a waste of money.
Steve Greenfield AE7HD
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Peter_n

rlogiacco, That is only 2 analog channels, I also want to capture more than 2 digital signals (SPI bus). And the software doesn't run in linux.

polymorph, You are right of course, but I'm looking for a "budget" scope ::) . It doesn't have to capture everything that is going on. I was thinking about 10 to 20 times the maximum frequency. You prefer 20 times at least, so that will be 500kS analog and 80kS digital. I thought that it shouldn't be so hard for a 100 dollar scope, but now it seems that my specs are for a 200 dollar scope :'(

I was hoping that someone made a shield for the Arduino Due (or Raspberry Pi, or Teensy). A shield with an ADC with parallel outputs, some memory and logic. I can almost draw the schematic.

larryd

Save your money save some more then buy the next level up.
No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

nilton61

If you are elegible as a student or academic you can get a discount on Digilents Analog Discovery

JimboZA

I recently got one of these; very happy with it for hobby use, and adequate for my needs.

4000ZAR is just under 400USD, 300EUR, 250GBP.
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Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

CrossRoads

#9
Nov 27, 2014, 06:54 am Last Edit: Nov 27, 2014, 06:54 am by CrossRoads
All the engineering students at Rensselar Polytechnic Institute, the oldest technological research university in the US (founded in 1824), are required to buy and use the Digilent Analog Discovery in their lab classeswww.rpi.edu
My son has one and says it works quite well.

I myself have a GW Instek GDS-2204A, a much more expensive 200 MHz 4-channel Visual Persistence DSO.
http://www.gwinstek.com/en/product/productdetail.aspx?pid=3&mid=7&id=1349
Captures 8 MHz SPI signals very nicely!  I also use a Saleae Logic (8) sometimes. Depends on what is being measured. https://www.saleae.com/

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Peter_n

#10
Nov 27, 2014, 07:42 am Last Edit: Nov 27, 2014, 08:15 am by Peter_n
nilton61 and CrossRoads, that Digilents Analog Discovery is awesome, and only 99 dollars for U.S. students (but 279 dollars for me).

The Saleae Logic is very nice. But digital capturing is 12MS/s cost 99 dollars (too slow) and 100MS/s cost 199 dollars (to expensive).

I can buy so many other things for 200 dollars/euros. I guess I have to wait a few more years.
Thanks for the help everyone, but I probably won't buy an oscilloscope.

CrossRoads

Shop your local electronics flea market too.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

TomGeorge

Hi, look up  on the internet for Amateur (Ham) Radio Clubs, check out when they have flea markets etc, a lot of surplus equipment, Dayton especially.
Check at ARRL web site for US stuff.

Tom....... :)
Everything runs on smoke, let the smoke out, it stops running....

Peter_n

...flea markets etc..
I might even find my own analog oscilloscope, I sold a few year ago  :smiley-mr-green:

polymorph

A digital logic analyzer paired with an inexpensive analog scope can go a long way on a budget.

Or a Bus Pirate V3 is made specifically to handle things like SPI and I2C signals. Seeed Studio is $27USD for the Bus Pirate 3.6, and $5 for the connector and probes.

http://www.seeedstudio.com/depot/bus-pirate-v3-assembled-p-609.html?cPath=174

http://www.seeedstudio.com/depot/Bus-Pirate-v3-probe-Kit-p-526.html
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

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