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Dajgoro
PostPosted: Sat Dec 10, 2011 3:43 pm 
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Hello!

I've been looking for a scope for a long time, but i can't find anything cheap enough. I can't invest too much money, and ebay doesn't offer a good solution. I would require that the scope is fast enough so i can track signals on my sbc projects. Any kind of scope is good, i don't care if is an old tube rca, or a modern usb.


Last edited by Dajgoro on Fri Dec 16, 2011 10:41 pm, edited 1 time in total.

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ChuckT
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PostPosted: Sat Dec 10, 2011 6:57 pm 
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The DSO Nano and DSO quad are cheap oscilloscopes but I don't know what you need in terms of speed:

http://www.seeedstudio.com/depot/index. ... es&x=0&y=0

The Beagleboard can be an oscillloscope. And the Beagleboard is more exciting.

http://www.youtube.com/watch?v=8qME7_Ez ... r_embedded
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Dajgoro
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PostPosted: Sat Dec 10, 2011 7:13 pm 
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Ye, but this kind of portable scopes are able to get to 1MHz max, and I need at least 5-10MHz, something like the RCA WO-33A(1965)...
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GARTHWILSON
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PostPosted: Sat Dec 10, 2011 8:06 pm 
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The DSO quad referenced has a maximum sampling rate of 72MSPS which is good (but certainly not overkill) for what you want (72MSPS puts the Nyquist frequency at 36MHz). It was the built-in signal generator that topped out at 1MHz. A major factor in oscilloscopes however is the quality of the probes; and there is no info on the Mueller mcx probes listed there. Mueller's own website doesn't even seem to have them. Good probes are not cheap. Although it would be nice to have the DSO features listed there, you might do well to just watch eBay for awhile to find a basic 20MHz (or higher) dual-trace triggered analog oscilloscope with a good pair of x10 probes included.

We had a good discussion on oscilloscopes at viewtopic.php?t=1617 .

I used my workbench computer last week to imitate a 4-input, 4-trace DSO with one of my cheap 20MHz dual-trace triggered analog oscilloscopes. Note that only one input is used (which comes from the workbench computer's D/A output) and the external trigger input is used (which the workbench computer gives a pulse to to start each trace). I probably should have sampled faster to get that third trace looking smoother, but it did the job. The workbench computer sampled four inputs and stored the samples in memory, then plays them back repeatedly for the analog 'scope to display.
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Dajgoro
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PostPosted: Sun Dec 11, 2011 4:09 am 
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The osd quad is 200$ without shipping, and i don't have so much money right now(i might have one day)... And i can't find any scope on ebay except the RCA WO for a reasonable price. But also nobody on ebay wishes to ship a scope by ship, only priority mail(~100$). Also there is the problem with the customs, last time that i ordered something more expensive 2x EL34 tubes, the customs charged me 50% of the actual price!
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ChuckT
PostPosted: Sun Dec 11, 2011 6:21 pm 
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Have you considered an FPGA oscilloscope?

http://www.fpga4fun.com/Hands-on_Flashy.html
http://www.fpga4fun.com/digitalscope.html

http://www.gabotronics.com/development- ... otolab.htm
http://www.gabotronics.com/development- ... inilab.htm

http://www.edn.com/blog/Designing_Ideas ... illips.php

I'm trying to remember the other company that had one to sell.


Xprotolab - Miniature Oscilloscope and Waveform Generator

http://www.youtube.com/watch?v=Q22tB7C- ... r_embedded
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Dajgoro
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PostPosted: Sun Dec 11, 2011 10:21 pm 
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Hmm, the fpga circuit looks interesting, this looks like something i might want to have as a sbc expansion...
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PaulF
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PostPosted: Thu Dec 15, 2011 1:10 pm 
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Whatever scope you get, make sure it has sufficient bandwidth for what you want to do with it. For microprocessor use, you need a bandwidth of at least 5 times the CPU clock and 10 times the CPU clock is required for pulses to look reasonably square.

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Dajgoro
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PostPosted: Thu Dec 15, 2011 1:13 pm 
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PaulF wrote:
Whatever scope you get, make sure it has sufficient bandwidth for what you want to do with it. For microprocessor use, you need a bandwidth of at least 5 times the CPU clock and 10 times the CPU clock is required for pulses to look reasonably square.

I've found a guy who is selling an HAMEG HM512 scope 60MHz 2 channel.
Will it do?
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GARTHWILSON
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PostPosted: Thu Dec 15, 2011 7:54 pm 
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If it is in good working condition and comes with good probes, it should be a really good addition to your workbench. Again, remember that the quality of the probes is a major factor.

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Dajgoro
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PostPosted: Thu Dec 15, 2011 11:40 pm 
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The seller offers a unused probe with it, and i think i have some probes home already...

Edit: I have also a Eico tube frequency generator(found it in the attic), it actually works with a range form 150KHz to ~100MHz(proof: radio receiver turns quiet when i match the frequency), but the output is not 5V, i can't really tell what is the output voltage, and there is some voltage present on the housing, someone replaced the cable and used a cable without ground.
I found inside that there are some two sticky brown components, i supposed some kind of leaked oil capacitors, one end of them is connected to the housing, and the other two to the ac input L and 0. And they seem to cause the voltage present on the housing, if i turn the plug one way i get some greater voltage, and i found that after i got a nasty shock, and if i turn the plug the other way the voltage is still there, but lower.
I would want to try to make a Schmitt trigger circuit so that i can use it as a clock source for testing my circuits.
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GARTHWILSON
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PostPosted: Fri Dec 16, 2011 1:39 am 
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Quote:
I would want to try to make a Schmitt trigger circuit so that i can use it as a clock source for testing my circuits.

In a seminar I was in, they said that for a 60Hz interrupt rate for a product, they even connected an input pin of a microcontroller to the power line through a resistor of 22 megohms or more, just using the protection diodes at the microcontroller's input, since the few microamps of current was ok for them. Obviously you'll need a lower resistance to get any voltage with the input capacitance of the Schmitt-trigger circuit, and you'll want to bias it appropriately, but it's quite do-able.

A VFO (variable-frequency oscillator) I breadboarded (on a solder-type breadboard, not a solderless one) to slowly turn the 5V logic clock frequency up on my workbench computer to see how fast it would go is as follows (this is from my tiny ring binder that holds all the hardware documentation on my workbench computer and related projects):

Image

Another topic dealing with 5V oscillators is at viewtopic.php?t=1576 . It has more good links in it too, and my VFO shown there is a later, faster one.

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Dajgoro
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PostPosted: Fri Dec 16, 2011 12:56 pm 
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I'll stick with the Eico oscillator, because it has a big scale, so i can set the frequency quite precise.
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GARTHWILSON
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PostPosted: Fri Dec 16, 2011 7:28 pm 
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I have a Fordham SG-490 (a re-badged B&K Precision 2005B) RF signal generator, but opting for the 74HC digital VFO was easy because the SG-490 only puts out a sine wave (with some distortion); and I also have a Heathkit IM2420 frequency counter good to over 1/2 a GHz, with 8 digits and several really nice features. I have a sweep function generator but it only goes up to 2MHz.

Attachment:
FordhamSG-490RFsigGenSmall.jpg
FordhamSG-490RFsigGenSmall.jpg [ 78.72 KiB | Viewed 6720 times ]

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BigDumbDinosaur
PostPosted: Fri Dec 16, 2011 8:47 pm 
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GARTHWILSON wrote:
I have a Fordham SG-490 (a re-badged B&K Precision 2005B)...also have a Heathkit IM2420 frequency counter...

It's good to see vintage test equipment still on the job. The old stuff may not be as fancy as the new stuff, but most of the old stuff was high quality in every respect, which is why it continues to function after all these years.

I'm still lamenting the loss of my Beckman Industrial scope that kept the northeast corner of my bench warm for so many years. But not to worry! A genuine H-P 1725A (275 MHz) scope is now holding down the fort. This is 1980's vintage technology that was refurbished by a former Agilent tech, and it works like a charm. The Ø2 signal on my POC unit actually looks like a square wave for a change. :lol:

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