EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: SuperMiguel on October 16, 2010, 02:10:03 am
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A local person is selling an Tektronix 2225 in good conditions for $75... Should i just jump into this? or should i save to get the rigol 50 Mhz one?
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Go for it!
If it's in good condition, it's worth more than $75.
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Honestly I'd consider both. I've been saving for a Rigol since March, but bills keep popping up, though I did jump on an old 465B for twice that price. There's nothing wrong with having two scopes, especially one analog and one digital as they have different strengths in the low budget price range (low noise vs. single shot capability and auto measurements). If it's truly in good shape then $75 is a good price. You can probably find old analog scopes with more bandwidth (100MHz to 200MHz is fairly common), but it can be a pain to find one locally depending on where you are.
Whenever I finally save up and buy a DSO, I won't be sad at all to have a solid analog to go with it. :)
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I have never use a scope before, so maybe its good ohysically but prob someyhing broken inside, I would not know, how can test it? Remember I never used one before, and this on has alot of buttons
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At the very least make sure it turns on and that you can see two horizontal traces on the screen. I'd say $75 is about the going rate for 2225's on ebay, so it's not that great of a bargain.
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do i have to do anything to see the horizontal lines?
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make sure it is set up correctly :P essentially you should get two lines by turning it on and selecting both channels. there should be a test output, get you friend to connect it up so that you can see it working of it's own internal calibration signal generator
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I've got a 2225 and the service manual to go with it (available from Mauritron services). It's a good scope and easy to use. The switch contacts may need a good cleaning with Servisol contact cleaner though if you buy it.
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If you can get a good 5MHz square wave to put into both channels, and compare them against the same at 1kHz, you can eyeball frequency response easily. It should check all the scopes basic capacity in one test.
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A local person is selling an Tektronix 2225 in good conditions for $75... Should i just jump into this? or should i save to get the rigol 50 Mhz one?
pay and take it, fast! dont ask any question! save money for rigol later...
this one selling calibration i think (USD395), and shipping ~= 2x calibration price... http://cgi.ebay.com.my/Tektronix-2225-50-MHz-2-channel-scope-NIST-certified-/350356739114?pt=BI_Oscilloscopes&hash=item5192e3942a (http://cgi.ebay.com.my/Tektronix-2225-50-MHz-2-channel-scope-NIST-certified-/350356739114?pt=BI_Oscilloscopes&hash=item5192e3942a)
and this one shipping is more than 4x the unit price (USD90)... http://cgi.ebay.com.my/Tektronix-2225-Oscilloscope-/250657328526?pt=BI_Oscilloscopes&hash=item3a5c574d8e (http://cgi.ebay.com.my/Tektronix-2225-Oscilloscope-/250657328526?pt=BI_Oscilloscopes&hash=item3a5c574d8e)
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If you can get a good 5MHz square wave to put into both channels, and compare them against the same at 1kHz, you can eyeball frequency response easily. It should check all the scopes basic capacity in one test.
How do I generate that signal?
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Word of warning - check the focus, brightness, horizontal course and fine pots first - if worn the replacement ones are very difficult to get hold of. The 15 odd year old unit I use at work has triggered trace jumping about the screen because the horizontal pots are worn. A few years ago the brightness pot needed replacement and I was VERY lucky to get hold of a replacement pot from Megger because it is no longer made and it was the last one they had!
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The one I have had a problem with the focus. The fault was one resistor in the focus chain that had burnt out. I replaced this and everything was OK. I did buy a spare pot just in case.
Sphere research ( http://www.sphere.bc.ca/ (http://www.sphere.bc.ca/) ) is a good source of parts and the Tekscopes yahoo group ( http://tech.groups.yahoo.com/group/TekScopes/?yguid=330951138 (http://tech.groups.yahoo.com/group/TekScopes/?yguid=330951138) ) is a good source for help.
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You'd need a good function generator, the seller may have one. How its used:
http://www.google.com/url?sa=t&source=web&cd=2&ved=0CBcQFjAB&url=http%3A%2F%2Fwww.kennethkuhn.com%2Fstudents%2Fee351%2Ftext%2Fsquare_wave_testing.pdf&rct=j&q=square%20waves%20amplifier%20pdf&ei=RvS5TPCnBoGClAe1_7mkDQ&usg=AFQjCNHNMdjks7pxoYwIsqxfSqfc_iR-kA&cad=rja (http://www.google.com/url?sa=t&source=web&cd=2&ved=0CBcQFjAB&url=http%3A%2F%2Fwww.kennethkuhn.com%2Fstudents%2Fee351%2Ftext%2Fsquare_wave_testing.pdf&rct=j&q=square%20waves%20amplifier%20pdf&ei=RvS5TPCnBoGClAe1_7mkDQ&usg=AFQjCNHNMdjks7pxoYwIsqxfSqfc_iR-kA&cad=rja)
Although the pdf is about audio amplifiers, the same principles work for a scope's input amplifiers. To see the tracing well, you'd have to work the controls too, and this would test any problems with them, as well as the quality of the screen.
If you can get a good 5MHz square wave to put into both channels, and compare them against the same at 1kHz, you can eyeball frequency response easily. It should check all the scopes basic capacity in one test.
How do I generate that signal?
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Got it and everything seems to be working fine... i have a simple question:
When im analyzing a simple LED flashing i only see a dot on the screen, i cant get a line that makes a square wave why is that??
video-2010-10-16-18-16-23 (https://www.youtube.com/watch?v=0-K_M9505rQ#)
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The LED is flashing too slowly for the CRT display persistence to keep up with and display a solid line. Try looking at some higher frequency signals, such as the probe compensation output.
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i did an arduino program with a 10ms flash rate and still not able to see it.
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100 Hz is pretty slow. Try a few orders of magnitude faster! Does the probe compensation output on the scope work?
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what do you mean by Does the probe compensation output on the scope work?
not sure what the probe compensation is
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Most oscilloscopes have a built-in square wave generator with an output somewhere on the front panel. This is used to tune the capacitance of your probes, which usually have a small tuning knob in them somewhere, to make the squarest-looking square wave.
Looking at a photo of the 2225, it appears that the output is labelled "PROBE ADJUST". Connect the probe to this and the ground to a suitable ground point, such as the outer rim of the EXT INPUT BNC connector, if you have an alligator clip for a ground.
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yes that displays a perfect square wave...
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yes that displays a perfect square wave...
Good! The signal you were generating with your Arduino is just too slow. This isn't a problem with the oscilloscope, just the display technology.
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if i just create a on and off program with out a delay.. that will get me 10 Mhz right? wil that be fast enough?
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if i just create a on and off program with out a delay.. that will get me 10 Mhz right? wil that be fast enough?
If you're using the digitalOut() functions (or whatever they're called), then possibly not - it's my understanding that these functions have some mysterious overhead and are quite slow, so you'd need to access the port directly the toggle with at top speed. No harm in trying, though - it would be an interesting experiment to calculate how much overhead the Arduino library has for this function by comparing the frequency you get to the theoretical maximum.
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i cant get a line that makes a square wave why is that??
Because your signal is to slow.
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if i just create a on and off program with out a delay.. that will get me 10 Mhz right? wil that be fast enough?
the fastest i can crack the Arduino to generate frequency using assembly is MIPS/4 (4 ops). so if AT1280 is at 16MHz, it only capable of generating 4MHz signal. but thats in assembly. In Arduino IDE? digitalOut? dont dream it! i can say the overhead will be like 36 ops (the fastest).
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You could whip together a quick 555 oscillator circuit that would give you a number of signals to view on your scope.
http://www.kpsec.freeuk.com/555timer.htm (http://www.kpsec.freeuk.com/555timer.htm)
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You could whip together a quick 555 oscillator circuit that would give you a number of signals to view on your scope.
http://www.kpsec.freeuk.com/555timer.htm (http://www.kpsec.freeuk.com/555timer.htm)
yup! to get faster signal, you should go analog, or... "Op Amp Hours"!
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If that video is true, that scope looks to be in great shape. A super steal for $75.
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You could whip together a quick 555 oscillator circuit that would give you a number of signals to view on your scope.
http://www.kpsec.freeuk.com/555timer.htm (http://www.kpsec.freeuk.com/555timer.htm)
Hoe fast should I make it?
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Hoe fast should I make it?
quick check the datasheet indicates 555 only run up to 500KHz. but i can be mistaken. so i'll leave the detail to the original suggestor. here is one basic op amp thread thats good for beginner like me https://www.eevblog.com/forum/index.php?topic=791.0. (https://www.eevblog.com/forum/index.php?topic=791.0.) maybe you can check the Arduino Oscillator pins to get faster signal, but should make the V/div to minimum i think.
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A 0.1uF cap and (R1+2R2)= 1Kohm should put you about 10KHz, which should do find to see stuff on your scope.
Here's another site that I refer to frequently when I'm mucking around with 555 circuits....
http://home.cogeco.ca/~rpaisley4/LM555.html (http://home.cogeco.ca/~rpaisley4/LM555.html)
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A 0.1uF cap and (R1+2R2)= 1Kohm should put you about 10KHz, which should do find to see stuff on your scope.
Here's another site that I refer to frequently when I'm mucking around with 555 circuits....
http://home.cogeco.ca/~rpaisley4/LM555.html (http://home.cogeco.ca/~rpaisley4/LM555.html)
will use one of this http://www.radioshack.com/product/index.jsp?productId=2102589 (http://www.radioshack.com/product/index.jsp?productId=2102589) have to go purchase it today, and test
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So i made a 555 timer using 2 x 330 ohms resistors and a 0.1uf cap using a 9v input which gives me a 14KHz frequency...
So i set my oscilloscope to: Sec/Dvi = 20 microseconds and 10V on the 10x probe and got:
video-2010-10-19-19-53-06 (https://www.youtube.com/watch?v=UlBbvLRMJOQ#)
why is it flickering?
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Could be unstable triggering? Try playing with the trigger level.
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I'd also try looking at it over a long time scale (50, 100, 1000ms/div, etc.) to see if the oscillation remains stable over time, or if it's stopping and starting.
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Could be unstable triggering? Try playing with the trigger level.
That was it :)
(http://lh3.ggpht.com/_gh5Sm-hBmxM/TL42FStPouI/AAAAAAAADdc/ASeShNGUX7I/s400/2010-10-19%2020.21.05.jpg)
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Awesome :) And congrats, seems like that scope was a great score!
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the flickering thing seems unusual. its like some power surge in our home and our lamplights start flickering ???
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the flickering thing seems unusual. its like some power surge in our home and our lamplights start flickering ???
Whats the deal with ground?some people tell me that yhe scope is grounded directly to the wall jack and that I should not need the ground cable, but if I dont use it, I cant get a signal...
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Whats the deal with ground?some people tell me that yhe scope is grounded directly to the wall jack and that I should not need the ground cable, but if I dont use it, I cant get a signal...
Ground is just a reference potential. The safety ground of the scope is the scope's reference, true, but most low voltage circuitry will be at a different (usually oscillating due to noise) potential. By linking the two grounds they're both working from the same reference.
Think of it this way, say you switch the scope to DC coupling and put the probe on the positive terminal of a 9V battery. Nothing happens, or at most you get some noise. There's nothing completing the circuit from the other side of the battery to the scope (or saftety ground), so the scope can't measure anything. The battery is at a 'floating' voltage, the grounds are unrelated. By connecting the probe ground you complete the circuit. You could connect the negative terminal of the battery to safety earth and get the same result, but there would be a lot more noise because the current has a huge loop (antenna) to flow through.
To see this effect in action, try setting your scope to about 200mV/div (AC or DC coupling) and touch the end of the probe with your finger. This is the same as holding the tip of a cable attached to a guitar amp. That horrid buzzing is now a waveform on your screen. You may have to do some work to dial it in, and you'll see it best if you switch your trigger to 'Line' (triggers directly off of the AC line voltage). This is a floating measurement using you as an antenna. Try the same thing with one hand near a dimmable light or adjustable fan and you'll see the horrid waveforms that triacs emit.
Any circuit that's referenced to safety earth (ground or otherwise) won't require the probe ground, but it's still useful. By using it you cut out a huge amount of loop area and cut your noise down to a minimum. In a floating circuit you can also take differential measurements between any two points because you're free to define your measurement ground by whatever you clip your probe ground to. For example you could swap the battery around and you'd get negative 9V on your scope (well, a bit more than 9V, check a fresh one with a meter to see what I mean).
Hope that helps some. If I messed anything up I'm sure folks will set me right. :)
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the flickering thing seems unusual. its like some power surge in our home and our lamplights start flickering ???
Whats the deal with ground?some people tell me that yhe scope is grounded directly to the wall jack and that I should not need the ground cable, but if I dont use it, I cant get a signal...
no it got nothing to do with ground. what i meant is, its analogous to the Home Main Power Surge. maybe something is playing up inside, dead caps maybe? i dont know, that cause the flickering. ???
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the flickering thing seems unusual. its like some power surge in our home and our lamplights start flickering ???
Whats the deal with ground?some people tell me that yhe scope is grounded directly to the wall jack and that I should not need the ground cable, but if I dont use it, I cant get a signal...
no it got nothing to do with ground. what i meant is, its analogous to the Home Main Power Surge. maybe something is playing up inside, dead caps maybe? i dont know, that cause the flickering. ???
Well yhe flickering was fixed by adjusting the trigger level
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Well yhe flickering was fixed by adjusting the trigger level
oic. from the video you provided, it seems to me that the trigger level is set correctly, just flickering. now i think i'm start to envy you, its lucky for you there is local guy to sell such thing. as other said, its super steal! now suggestion: to improve the value of it, maybe you can fix the dented screen frame on the top left, so your scope will looks much better and... like new! ;D ;)
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So i installed Audio ToolBox to generate few signals from my audio card and i have a question so i set the sine wave to 10KHZ:
(http://lh4.ggpht.com/_gh5Sm-hBmxM/TL8oWMHgu7I/AAAAAAAADds/MmQv9X5dcRk/s400/2010-10-20%2013.34.36.jpg)
and i get:
(http://lh6.ggpht.com/_gh5Sm-hBmxM/TL8kZGWSwLI/AAAAAAAADdg/PVvhgoZOGtU/s144/2010-10-20%2013.18.00.jpg)or
(http://lh5.ggpht.com/_gh5Sm-hBmxM/TL8oOZowjCI/AAAAAAAADdk/AeiiobJQkE8/s144/2010-10-20%2013.34.16.jpg)
if i change the type from sine to square i get:
(http://lh6.ggpht.com/_gh5Sm-hBmxM/TL8pOZXhWGI/AAAAAAAADdw/Wciym-1pqIE/s144/2010-10-20%2013.38.34.jpg)
why is that?? why im not getting a square wave??
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If your sound card is set at a sampling rate of 44100Hz (which is usually the default), it'll only be able to produce frequencies up to 22kHz. A square wave is made up of a sum of sine waves (see: Fourier series), with the main contribution being the original frequency, and other harmonics at odd multiples of it. Since 30kHz signals can't show up from your sound card, it'll look weird like that.
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If your sound card is set at a sampling rate of 44100Hz (which is usually the default), it'll only be able to produce frequencies up to 22kHz. A square wave is made up of a sum of sine waves (see: Fourier series), with the main contribution being the original frequency, and other harmonics at odd multiples of it. Since 30kHz signals can't show up from your sound card, it'll look weird like that.
set it to 5KHz and (http://lh5.ggpht.com/_gh5Sm-hBmxM/TL8z44hubZI/AAAAAAAADd0/GAXp_U_nE1I/s400/2010-10-20%2014.23.25.jpg)
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Please see this: http://en.wikipedia.org/wiki/Fourier_series (http://en.wikipedia.org/wiki/Fourier_series)
A 10kHz square wave can be decomposed into a sum of sine waves of frequencies 10kHz, 30kHz, 50kHz, etc. The higher frequencies are what makes it look like a square wave instead of a sine.
edit: your 5kHz square wave looks as expected. Looks like the second image here, which is the sum of sine waves of the original frequency and at 3 times the original frequency: http://en.wikipedia.org/wiki/File:Fourier_Series.svg (http://en.wikipedia.org/wiki/File:Fourier_Series.svg)
The higher frequencies, at 5 * 5kHz, 7 * 5kHz won't show up.
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You're getting closer. To get a square looking wave, divide the top most frequency by ~ 10, its really the 9th harmonic, but 10 is easier to remember. If you can generate and see without distortion, the highest harmonic, then you can likely see all the top intervening harmonics too: 3,5,7,9.
If the top frequency is 22kHz, to see a nice sq. wave use ~ 2kHz.
If your sound card is set at a sampling rate of 44100Hz (which is usually the default), it'll only be able to produce frequencies up to 22kHz. A square wave is made up of a sum of sine waves (see: Fourier series), with the main contribution being the original frequency, and other harmonics at odd multiples of it. Since 30kHz signals can't show up from your sound card, it'll look weird like that.
set it to 5KHz and (http://lh5.ggpht.com/_gh5Sm-hBmxM/TL8z44hubZI/AAAAAAAADd0/GAXp_U_nE1I/s400/2010-10-20%2014.23.25.jpg)
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Yep... looks about as good as a sound card could probably produce... I bet at around 1K it would look almost there. ... just depends on how many harmonics the sound card can produce at once.... if it will only produce 4 or 5 odd harmonics at once then you probably won't get much better.
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changed it to 2KHz and got:
(http://lh6.ggpht.com/_gh5Sm-hBmxM/TL86KT3dVxI/AAAAAAAADd4/sEqx8seWZnk/s800/2010-10-20%2014.51.02.jpg)
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I agree with strube09, you're getting really close. The estimate of 22kHz was a ball park figure, but lower it to 1kHz and see.
Yep... looks about as good as a sound card could probably produce... I bet at around 1K it would look almost there. ... just depends on how many harmonics the sound card can produce at once.... if it will only produce 4 or 5 odd harmonics at once then you probably won't get much better.
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This is kind of a great experiment to show how/where square waves really come from.... The pictures really show it in this thread vs. some drawing in a book.
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1KHz
(http://lh5.ggpht.com/_gh5Sm-hBmxM/TL9Y1TYM4qI/AAAAAAAADeE/t6FMfPiDCt4/s400/2010-10-20%2017.01.51.jpg)
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It looks like those added waveforms are ringing artifacts caused by, possibly the Gibbs phenomenon particulary when looking at the artifacts at 2 kHz:
http://en.wikipedia.org/wiki/Ringing_%28signal%29 (http://en.wikipedia.org/wiki/Ringing_%28signal%29)
This occurs when the generator of the square wave, if it actually made by summing multiple sine waves together and mixing harmonics 9,7,5,3,etc., of the fundamental to create a square wave, but does do it imperfectly or misses some of the key harmonics, it will create artifacts.
http://en.wikipedia.org/wiki/Gibbs_phenomenon (http://en.wikipedia.org/wiki/Gibbs_phenomenon)
Nevertheless, the scope can pick it all up easily!
quote author=SuperMiguel link=topic=1535.msg20877#msg20877 date=1287608693]
1KHz
(http://lh5.ggpht.com/_gh5Sm-hBmxM/TL9Y1TYM4qI/AAAAAAAADeE/t6FMfPiDCt4/s400/2010-10-20%2017.01.51.jpg)
[/quote]
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This is kind of a great experiment to show how/where square waves really come from.... The pictures really show it in this thread vs. some drawing in a book.
I agree
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can be a reminder for me too on this harmonics application ;)
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so far everything has worked with the scope... so i think it was a good buy for $75 .... Thanks all of you that helped me made the decision and then helped me test it :) thanks