student needs simple circuit to generate sine, square, triangular wave: suggestions or ideas for fixing what we have

[Michael Shiloh]

Hi!

Accuracy not at all important. It's for a noise maker.

We tried the Forrest Mims circuit using two 1458s but while the first
op-amp correctly generates a square wave, the subsequent op-amps fail to
integrate it to a triangle and then a sine wave.

http://ecelab.com/circuit-function-gen.htm

I had my student rebuild the circuit to reduce the chance of errors and
shorts, but no luck. I inspected it closely and it seems correct.

Any tips on fixing this appreciated, although we are also open to other
ideas. I rather like the old ICL8038 but these are unavailable and I
don't know what other single chip function generators exist.

M

Michael Shiloh
Artist, designer, tinkerer, teacher, geek
KA6RCQ
michaelshiloh.pbworks.com
www.teachmetomake.com
teachmetomake.wordpress.com
http://groups.google.com/group/teach-me-to-make

[Jon Wagner]

Michael,

What frequency is the square wave? If its too slow, the integrator will just rail out and look a lot like a square wave. This would indicate a problem in the astable vibrator section of the circuit.  

If that's not it, the only other thing I could think of is that your capacitor is not acting like a capacitor (component no good) or the resistor values in the second stage are not correct.

Jon

[Michael Shiloh]

Ah! Good point. I'll check that today.

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[Jon Wagner]

I should have said:
the RC integrator which makes the "triangle wave generator" needs to
be tuned to the frequency of the square wave generator portion of the
circuit. I think the values in the link you sent should result in a
system that works, but if you were to deviate much, you could easily
end up with a square wave out of the "triangle" section, or on the
other end of the spectrum, a very low amplitude triangle wave.
Jon

On Apr 9, 10:56 am, Michael Shiloh <michaelshiloh1...@gmail.com>
wrote:

[Jon Wagner]

Just to pollute the list with more babble - my advise is to go buy
this chip and be done :)
http://search.digikey.com/us/en/cat/integrated-circuits-ics/clock-timing-programmable-timers-and-oscillators/2556130?k=function%20generator

[Michael Shiloh]

great idea. i'll try that too.

at this point, the student is happy with square wave. i'm still going to
experiement with reliable ways to produce sine (and other) waves for
future projects.

m

[Steven Nelson]

This looks like a fun project..  http://www.lushprojects.com/vpc/ 

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