EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: xani on April 10, 2010, 03:14:51 pm
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Im thinking about buying this: http://translate.google.pl/translate?hl=pl&sl=pl&tl=en&u=http%3A%2F%2Fwww.ambm.pl%2Findex.php%2Furzadzenia-kontrolno-pomiarowe%2Fdd1a.html (http://translate.google.pl/translate?hl=pl&sl=pl&tl=en&u=http%3A%2F%2Fwww.ambm.pl%2Findex.php%2Furzadzenia-kontrolno-pomiarowe%2Fdd1a.html) for my mini lab but it doesn't generate triange wave, just sinus and square and im wondering if i should ge thos or "normal" func. generator. How useful is triangl wave out ?
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It's useful for testing amplifiers, it's much easier to see distortion and clipping than with sine waves. It's also useful for testing comparators.
This seems quite different from a regular function generator. A function generator can usually generate sine/square/triangle waves from 1Hz to a few MHz, with amplitudes up to 20V in a high-Z load. Most offer symmetry adjustment (adjust duty cycle for square waves and makes triangle waves into ramps). The frequency stability is usually lousy, especially for the non-DDS ones.
This seems more targeted at the RF segment, more like a signal generator with a square wave thrown in. The frequency range is much higher, the amplitude is lower (max 2Vp-p in high-Z load). Max 5mV offset. Probably fairly good stability since it's DDS. The spectral purity at 1Vp-p, 1MHz looks quite good (all harmonics < -57dB or so). The square wave is pretty fast (<8ns rise/fall time), but has a fixed output amplitude. Not very useful for eg. 3.3V logic.
It may be a fine unit for the intended use, I have no experience with this product, but the specs seem pretty good. It seems less versatile than a normal function generator (which is the jack-of-all-trades of signal sources), as long as you don't need the extra range, stability or purity.
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Im wondering what i should get because for similiar price i can get typical 2-3MHz func. gen. For now i plan to use it for audio/SMPS (and i plan building tesla coil ^^ ) but after seein EEVBlog Instek review i didnt like that "wobbling" in wave frequency and thats why im wondering if i should get that DDS gen.
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Well there is another alternative .. way .
All that you need are one generator , in KIT with one TL082 ... ( that you have to assemble by your self ) , and one Frequency counter ..
I have make this setup for my self , but I own one good frequency counter ,
the LEADER LDC-831 .
As alternative of the dedicated frequency counter , you can use an multimeter with such ability , it would possibly cost less.
Still , the only issue with this setup , its that you have to tune it , its time that you like to use it,
by using both devices simultaneously .
Just an idea ..
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I can always use scope for that ;)
Well i have ICL8038 so i could make like 100kHz func. gen with it but its kinda low compared to cheapest func. gen. and i'd still have to make all that additional circuits (frequency sweep, DC offset etc.) to make it comparable to even cheapest func. gen.
I guess I'll go with normal func. generator for now, i dont need such high freq generator for now and things like frequency sweep sounds quite useful for what i'll be doing
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Well , I have buy this gen. about 15 years back , from a Greek company called as " Smart Kit " ,
it has lots of Kits .
I just visited their page , and found the link ..
So have a look, to see what I am talking about.
http://www.smartkit.gr/details2.php?lang=1&wh=6&searchttile=1008&thepid=119&lang=2 (http://www.smartkit.gr/details2.php?lang=1&wh=6&searchttile=1008&thepid=119&lang=2)
There are four potentiometers on it ...
The first adjusts the frequency ,
the other three adjust the outputs , of its signal .
It has three separate outputs .
sinusoidal - triangular - square .
About the range it is 20 Hz and 20 KHz , with three scales selector .
Because of this thread , I took in my hands , so to test it , I do not use it much this days .
And found the frequency potentiometer , to be out of shape ... ;D
I will probably exchanged , with a modern "10 turns" one , so to be easier to get tuned , with better accuracy .
Speaking about cost , even today it cost as 22 EUR or about 30$ . :)
(http://img442.imageshack.us/img442/2298/soundgenerator.jpg)
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i got one of similiar kits (it was 10Hz-100khz function generator) but in the end it was qute buggy schematic + it had just one "cover-it-all" range so even with 10 turn pot. it was hard to get some low freq wave out of it.
I was thinking about getting one of those 4-in-1 things like for example http://www.alibaba.com/product-gs/240859288/UNIVERSAL_SYSTEMS_DF6911.html (http://www.alibaba.com/product-gs/240859288/UNIVERSAL_SYSTEMS_DF6911.html) as i need some decent power supply and 2nd multimeter and im wondering if that wouldn't be better instead of dedicated generator
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A triangle wave is very useful use in Telecommunications, analog encoding of audio (PWM signals, for example in class D amplifiers). Missing out on that for a DDS generator is quite a bad thing I suppose.
Though you can easily create a little triangle generator if you know the frequency with an opamp, resistor and capacitor.
(http://www.ece.osu.edu/ee327/Figures/integrator_schem_large.gif)
You would need to calculate the R and C for the specific frequency you would be working on, because it's related to tau (tau = R*C). Just take a capacitor for you frequency range and a 10k pot so you can shift it a bit around. The input is just a basic 0V to 10V square in this case.
So; having it built is very useful, but if you only use it so rarely (as it seems, because you're asking us how useful it is ;)) you could get away with building a circuit up for it everytime. In the end you can't keep your devices connected to a function generator all the time, so building up a square to triangle wave is something you would have to do anyway.
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yeah, but then atm i dont need high freq. generator either, so i was wondering what's better, to have more availble freq or be able to generate triange + frequency sweep + wave width regulation, now im thinking that "real" function generator would be more useful ;]
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i got one of similar kits (it was 10Hz-100khz function generator) but in the end it was qute buggy schematic + it had just one "cover-it-all" range so even with 10 turn pot. it was hard to get some low freq wave out of it.
My generator has an three range selector !!
About you last question ... " usability "
Well , now that we have set all the options, of tools , on table ..
I will say that in my generator , even if it has three outputs on the PCB , my box has only one ;)
The other two are connected with thin air ...
I work with repairs of sound equipment , mixers and amplifiers , for home use and large dancing halls .
Primarily what is needed are the acoustic range , 80Hz - 9kHz .
For acoustic frequency's testing , you need other the sound generator , one fasma-scope.
( well my English does not helping me here , but I am trying ) :)
fasma-scope or fasmatoscope ... its a graphical interface , equal of what we see in some cheap, and high end EQ devices ( Equalizers ) , that they have one little screen in the center , with led bars , one for every "base" frequency ..
Kenwood had build one fantastic EQ , with 16+16 "base" frequency's and a huge "spectrum analyzer" display, on it .
With all this tools , I was able to check the total frequency response , of the device that I was testing.
So , the importance of the generator it self , has a little value , if there is no " fasma-scope or fasmatoscope or spectrum analyzer with display , at the end of the chain .
Ok ... theoretically , you can insert an single signal as 1kHz as example, and measure the output in mV ,with a simple multimeter , but this are the theory ... in praxis you need " real " tools = more advanced .
In SUM , you will need just one simple sound generator.
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If you want an audio signal generator and spectrum analyser then consider using a PC sound card.
I posted this a few days ago:
I came across this website a while ago...
http://www.sillanumsoft.org/ZRLC.htm
I've used older versions the software for some time and the Spectrum Analyser works well,
the latest version has the facility to measure R, L & C with a simple external circuit (two OP-Amps and a few resistors + decoupling!).
Jim
Can also generate two channels of sine, square, triangle, noise etc. with frequency sweep if required.
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My scope has FFT ;D and yeah u can always use soundcard. But i wanna play with things like SMPS and Tesla coils.