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Setting up your own project constraints

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Lord_Nikon

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Hello world,

I'm about to start designing my own signal generator for test purposes. I like to work with audio circuits. So it's intended use is for testing audio filters and the like. Anyway, I've set up a few project constraints for myself to follow. I just wanted yall's input. Is there anything I should add to the list of constraints that would make this a better project? A lot of these are arbitrary and off the top of my head. Plus it's a personal project soo... I'm not too picky as long as the job gets done. I just want to make sure that I design a legit piece of equipment.

Here are my constraints:

-Must produce 3 basic wave forms (1 output with a 3-way select)
-Sinewave
-Square wave
-Triangle wave
-Must have variable frequency within audio range (20Hz - 20kHz)
-Must be able to run off a generic Wallwort for power
-Must have amplitude variation from 1V pk-pk up to 24V pk-pk

If you were building a signal generator what specifications would you add?
 
20 kHz is too low. Go fro at least 50 kHz, preferably 100 kHz. I have professional audio equipment rated 0-100 kHz and my power amp is intentionally rolled off at 40 kHz. The unrolled off -3db freq of that power amp is insanely nuts: 800 kHz.

Low distortion.

If your designing filters, then sweepable, possibly with a marker.
 
What you really are looking for is a function generator. These things are so cheap to buy these days from Ebay, you would save money just buying one.
**broken link removed**
 
What you really are looking for is a function generator. These things are so cheap to buy these days from Ebay, you would save money just buying one.
**broken link removed**

Thanks for the suggestion! I will probably end up buying one, one day. But the purpose of my project is to learn while doing. Thanks tho.
 
-Must produce 3 basic wave forms (1 output with a 3-way select) A auxiliary output to drive a frequency counter or to trigger an oscilloscope is usefull
-Sinewave
-Square wave
-Triangle wave
-Must have variable frequency within audio range (20Hz - 20kHz) Up to 50 or 100kHz would be better.
-Must be able to run off a generic Wallwort for power Consider an internal battery for low noise and portable applications, the battery can be charged by the wall wart.
-Must have amplitude variation from 1V pk-pk up to 24V pk-pk
24v is a lot of output, what are you going to drive with it?
Also 1v is too much for testing sensitive amplifiers. Consider adding an attenuator, unless you have or will build a separate stand alone attenuator.

Consider having defined output impedances, 600, 150, 75 Ohm etc.

JimB
 
Consider having defined output impedances, 600, 150, 75 Ohm etc.

JimB


Thanks! all great suggestions. 24V was just a random number. No real rhyme or reason. Just wanted a good range.
What would you base your output impedance on? If I'm designing for audio circuit testing is there a standard value that is used?
 
Thanks for the suggestion! I will probably end up buying one, one day. But the purpose of my project is to learn while doing. Thanks tho.
I totally get that and support your reason.
 
What would you base your output impedance on? If I'm designing for audio circuit testing is there a standard value that is used?
600 Ohm is in my experience the most common interface impedance for audio circuits and audio frequency test equipment.
I have also some audio test equipment which has the option of switching to 150 or 75 Ohm impedance.

JimB
 
Be aware that a function generator may not generate a very low distortion sinewave if you are interested in doing distortion tests.
 
The AD9833 chip might be what you want, you would have to use a PIC Micro or something to run it though.
https://www.analog.com/en/products/...hesis-modulators/ad9833.html#product-overview

Other than that as mentioned, the XR2206 will work and require no microcontroller, but also mentioned it has some distortion. BTW mouser has the XR2206 in stock. I am amazed as I thought the part was discontinued. I do think the 2206 can do AM.
Party on...
 
No need to buy anything.

Your PC can generate 0 to >270 kHz with software. ( enable Tone and Log display) then draw wave or select any waveform. select max playing f and max terms. Java based arbitrary waveform generator , or arbitrary spectrum with draw of std. wave form
https://www.falstad.com/fourier/ Each button selects a wave or processes existing wave ( e.g. High pass , rectify etc.
upload_2015-9-5_9-54-44.png

Then Audacity has Sweep Generator and Mic input record. or Speaker and Aux in., with Analyze Fourier spectrum, etc. use it as a sig gen, scope and spectrum analyzer/
 
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An ICL8038 is another Function Generator IC.
But the XR2206 is better.
 
You do not want a measurement of the harmonics (distortion) when you test the rolloff of an audio filter. Some function generators make a funny looking sinewave full of harmonics. The ebay function generator does not spec its amount of distortion or its level variation so maybe ebay does not want you to know how bad they are.
You also want the output level to stay the same when it is set at different frequencies.
 
For 15 bucks, I would not expect much, but for someone just starting out in electronics, I am sure it would be adequate. I think for someone just learning, they would not have the knowledge nor the equipment to discern the shortcomings of the instrument anyways. As their knowledge progresses, then a larger investment would be justified.
 
You can also use a CD4046 PLL which has a VCO that spans up to 2MHz or more at 15Vdc with by R or C selection.
using counters to scale many decades with precision.

Or you can make your own sine gen
Or a FM sweep gen

Or just a simple Triangle, Square wave gen.
upload_2015-9-7_16-15-47.png


adjust cap for 20Hz ~20kHz
 

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YOu can even use an MP3 swept freq. sine wave with >70dB SNR from your speaker or Aux out and Audacity to capture the response.
 
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