How to build a function generator

[V0ODO0CH1LD]

I have to deliver a project for my analog electronics course and I wanted to build a synthesizer (the simplest version possible since I am a total beginner at this). It would basically be a function generator with a knob used to control the frequency (with maybe banana plugs for sound output). How would I go about building this function generator from basic components like capacitors, resistors and diodes?

I read that a triangular wave can be generated by repeatedly charging and discharging a capacitor from a constant current source. How would the simplest version of this work? I have to actually build the project and I don't even know where to start.

 

[cpscdave]

http://2.bp.blogspot.com/-osSj6Rsg8L8/UBwhH-1w4_I/AAAAAAAAAIw/EoJ8McD15GY/s1600/tttttt+copy.jpg

try googling the types of signals you want, and then use something like falstad to test the circuits prior to building them :D

 

[V0ODO0CH1LD]

I guess the starting point is to build a function generator that generates only triangular waves. Can you point out any resources of tutorials on that?? Something that explains the function of each component on the circuit and all that!

Thanks!

 

[donpacino]

Fun fact, most triangle wave generators will also produce a square wave!
below is a link to a standard triangle wave generator.
First figure out how it works.
then figure out how you could make it variable frequency.

http://www.electro-tech-online.com/attachments/triangle-wave-oscillator-png.22625/

cpsdave: just followed your link. I guess I should read before I post... Great minds think alike!

 

[donpacino]

note: disregard the resistor and cap values, you'll have to choose those to suit your needs.

 

[thankz]

get the data sheet for the MAX038, maxim doesn't sell the chip anymore but if you look around you should be able to find it.

 

[skeptic2]

Hint: The integral of a square wave is a triangle wave and the integral of a triangle wave is very close to a sine wave. Biggest problem - amplitude varies with frequency so you would need automatic gain control.

 

[analogdesign]

The simplest way to do this is using a 555 timer. The timer signal itself is a sawtooth which is the typical waveform used most often in analog music synthesizers. If you need sine your can filter it.

 

[V0ODO0CH1LD]

Okay! Thanks for all the replies! After doing some research I've decided to construct the simple square wave generator shown in this link:

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/square.html#c2

I wanted to know what are the components I should buy if I wanted to build it so that it ranges over the audible frequency (20Hz - 20kHz). Could I just put a potentiometer where R is in that figure? What are the actual values of the components I should buy?

 

[analogdesign]

That will work but keep in mind it will probably be easier to make a 555-based square wave generator work than if you do it with an opamp.

That said, most standard Rs and Cs will work fine in audio frequencies. You can use a potentiometer for R but it is best to use the pot for only part of the R.

As for the values, you calculate what you need from the circuit description you linked to. All you have to do is pick Lambda and the period you want then everything else can be calculated. Be sure the common-mode range of the op amp you use is good enough to handle whatever value of lambda you choose.

Have fun!