HELP with function generator using IC 555 timer!

thatoneguy

Joined Feb 19, 2009
6,359
But after breadboarding the circuit has to go through Ultiboard to design a PCB.
The question i have here is that when transferring the circuit to ultiboard, the software gives a message that there is a large number (49 i believe) of virtual components that cannot be converted. Is this related to the components connected to the virtual ground?
Try to use real part numbers when inserting models, otherwise it will use "Ideal" virtual diodes, resistors, etc. Easiest way to know you are using the right component, make sure the device you choose has a dimensioned footprint of what you will use, SMD or Through Hole, there isn't a global option for this, just scroll through models of that part number.
 

thatoneguy

Joined Feb 19, 2009
6,359
I ruled out function generator IC's earlier on when i realized that they could not be simulated using Multisim. I needed to simulate the various circuits in Multisim so i could choose the best one.
I'll echo what Bountyhunter said:


http://www.eleccircuit.com/xr2206-function-generator/

It's not like you have any choices available to compare. That is the ONLY through hole function generator in active production. $2.96 from DigiKey, 8 pin DIP + 4 capacitors and 3 or 4 resistors for single supply operation. XR2206 Datasheet
 

Wendy

Joined Mar 24, 2008
22,541
I tried using the Tl084 it did not help that much. I also read in Bill's function generator thread that the improper duty cycle of the square wave was due to the darlington configuration inside the 555 IC's. What aspect of the configuration causes the less than 50% duty cycle?
It has to do with the capacitor charge curves. If the voltages are not symmetrical it throws off the charge curve, which throws off the duty cycle. It is explained more fully in this circuits cousin, 555 Hysteretic Oscillator, explains this in details with graphics. It is why I developed the transistor drivers in the other variation, and suggested you use a CMOS 555, which doesn't have the problem.

Come on guys, I think the OP has already explained he is doing this to understand the circuit theory. It was one of the reasons I did mine.
 

T.Jackson

Joined Nov 22, 2011
328
You're better off making a Wein Bridge-based generator.

http://www.google.com.au/search?q=w...s=org.mozilla:en-GB:official&client=firefox-a

This is still quite a respectable design even on a scale of today's standards. The amplitude is nice and stable across the entire frequency range, often by using a PTC incandescent lamp in the feedback path. The distortion is also very low as a result. You can evaluate audio gear with this oscillator.
 

Thread Starter

Narrin

Joined Oct 2, 2011
47
Thanks for the link Bill, that explains it. I got the PCB made today and I am going to solder the components in tonight.
What I would like to do when this project is finished is design another function generator from the start using a different circuit configuration and see how that goes.
 

TheLaw

Joined Sep 2, 2010
228
Sorry to sound stupid, but why was the design switched to a CMOS 555 from the regular higher output 555?

What is the "best' revision of Bill's design at this point? ie Most stable, best waveforms...

If I built one, I would power it from the wall.
 

thatoneguy

Joined Feb 19, 2009
6,359
Sorry to sound stupid, but why was the design switched to a CMOS 555 from the regular higher output 555?

What is the "best' revision of Bill's design at this point? ie Most stable, best waveforms...

If I built one, I would power it from the wall.
The CMOS 555 can go to nearly Rail to Rail on the output voltage, while the bipolar 555 can only go to 0V low and Vcc-1.5V on the output.

CMOS TLC555 can source 10mA and sink 100mA, while the bipolar LM555 can sink/source 200mA, though at a lower voltage.
 

TheLaw

Joined Sep 2, 2010
228
The CMOS 555 can go to nearly Rail to Rail on the output voltage, while the bipolar 555 can only go to 0V low and Vcc-1.5V on the output.

CMOS TLC555 can source 10mA and sink 100mA, while the bipolar LM555 can sink/source 200mA, though at a lower voltage.
So does that make the CMOS variant better for this app?
 

thatoneguy

Joined Feb 19, 2009
6,359
So does that make the CMOS variant better for this app?
Yes, for a function generator, it allows the output to be much more symmetrical. Since additional processing/buffering takes place on the output signal, the current sourcing ability isn't as big of a handicap as one would think.
 

TheLaw

Joined Sep 2, 2010
228
Oh alright I understand. Does anyone know what the most recent schematic is for this? I've been trying to piece together some of the input and I don't see a particular design that seems to be final.

Also would an op-amp with a very high slew rate can problems with stability. I was looking at the TLE2144. Quad op-amp. 25V/us, 85dB rejection ratio. Pretty good specs...but could it work with a non professional layout etc?

Also, is it better to have physically separate op-amps for each output to prevent crosstalk? Isolate them with shields grounded to chassis earth or something?
 
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Wendy

Joined Mar 24, 2008
22,541
Are you thinkin of building something like it? If you are I would start another thread.

When I came up with this circuit it was a concept circuit, not meant for real use. That didn't mean I didn't want it to work though. I may pick back up on it and using it for the book though. The OP of this thread has worked some of the bugs out it appears.
 
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