Homebuild Function Generator ..... HELP

[seadolphine2000]

homemade dds pic micro function generator

Hi,..

I wnat to build a small function generator using discrete components.
The generator specs are:
1- Waveforms: Square, sawtooth, sinusoidal.
2- Ouput voltage level: 5 volts (peak).
3- Frequency Range: 1K, 10K, 100K, 1M Hertz. (Only these values).

I can make a square wave generator and integrate it to get the sawtooth.BUT,...

How to get a sinusoidal from square or sawtooth.????

I can use PIC16F84 to make the square wave with these frequency ranges, integrating this square gives sawtooth with same frequency ranges.BUT,...

What about the sinusoidal.????

Any help will be deeply appreciated.

Thanks to all of you.

 

[IanP]

homemade function generator

Take a look at the ICL8038 function generator: **broken link removed**
For fixed frequecies you can put it in a PLL loop ..
If, for some reasons, you don't want to use this IC you can implement its idea of converting triangle wave into sine wave (detailed internal diagram included) ..
The ICL8038 is rated up to 300kHz but you can find equivalents from other manufacturers (Maxim, for example) which can work with frequencies well above 1MHz ..
Regards,
IanP

 

[ptmsl]

best 741 function generator

The simplest way of producing sinwave from triangle is to filter the higher harmonics. since your generator is not continiously adjustable you can use a second order filter with different components for each frequency. If you want to use a microcontroller then use PWM (pulse width modulation) or PDM (pulse density modulation) and an integrator (low pass filter at a fixed frequency) to produce a clean sinusoidal waveform. The easyest way however is to use the XR2206 chip from EXAR (www.exar.com). With the XR2206 and a few external components you can built a very reliable function generator up to 1MHz.

 

[huojinsi]

simple wienbridge audio 1 khz sine wave schematic

IanP'post is a good suggestion. ICL8038 is a classical function generator.

 

[jonw0224]

lm339 sawtooth

To convert from triangle to sine, you can design a waveshaping circuit, very similar to the one that Ianp suggests. I would say though, that the one on the datasheet is more complicated than most, which consist solely of resistors and diodes.

I think the low pass filter idea is simpler if you only want set frequencies.

Do you want triangle or sawtooth waveform? Triangle is easy (integration only), sawtooth take a little more work (integrate to slope up to 5V, then switch to 0V) but it's easy as well.

Are opamps allowed in the design?

I only post this because I'm not sure you have the function generator IC available in egypt. It you do, the function generator IC as Ianp suggests is best.

 

[seadolphine2000]

dds function generator

Thanks very much to all of you. I'll search for the chip suggested by Ianp but, In case I can't find it, I think I'll have to take that hard way.

Any component is allowed in the design. I've already made a square wave with the frequencies set above. Triangular is not a problem as it's only integration. The only problem is about the sinusoidal.

Please concentrate on the sinusoidal wave. I have an idea which is using a crystal oscillator then use a frequency divider.

Please, tell me what do you think.

Thanks to you all

 

[IanP]

ad9835 pic microcontroller based generator

Try to get free samples from Maxim ..
The part number is MAX038: **broken link removed**
**broken link removed**
It is the contemporary version of the old ICL8038 function generator with wider ranges ..
Regards,
IanP

 

[seadolphine2000]

ad9835 function generator

There's a problem in shipping to Egypt due to taxes,..etc. That's why they refused to send them.

Any other ideas.????

Thanks

 

[IanP]

lm339 sawtooth generator

Try in Egypt through High Technology Systems: **broken link removed**
Regards,
IanP

 

[seadolphine2000]

icl8038 functiongenerator

Thanks Ianp, but they don't offer shipping So,...
I think, I'll take the hard way and design it by myself.
I'm think about making wein bridge oscillator with varaible feedback networks. Is it correct.???

Thanks for help

 

[Davood Amerion]

diode breakpoint sine wave

Hi;
if you want make "tringular to sine wave" with disceret component, you can use 8038 idea.
it's idea use wave shaping from diodes switch on according to triangular input voltage .
and add attenuation in higher voltage.
you not need use transistor.
just 2*(3 diode) and its resistor.

next simpler approach is using 2 diode (in 2 direction) in non linear woking point.

second approach give you higher THD, but for "home made function generator" is enagh!

regards,
Davood amerion

 

[jonw0224]

homemade saw tooth generators

Another thought, you can use a sinewave oscillator (usually one opamp or transistor plus band pass filter in closed loop configuration).

Then, you can use a comparator to convert to squarewave and an integrator to convert the squarewave to a triangle wave....

I've built this before and it worked good. I've also built the square/triangle wave generator with the waveshaper for the sine wave. It worked good as well. The first choice is easier to design and requires fewer components. But the second choice is more flexible an can be tuned with a single variable resistor or capacitor.

To build the waveshaper, you can use diodes as Davood suggests. Basically, the circuit is a voltage divider, but the lower portion of the divider uses diodes to vary the resistance at different input voltages. The result, if you design it correctly, is that the output voltage changes more slowly with voltages further from zero so that you round the peaks of the triangle wave and get a sinewave.

An easy example of a waveshaper circuit is a 1 kohm resistor in series with a 1 kohm resistor in series with a diode whose cathode is connected to a 1V DC source. You apply a voltage at the top of the 1kohm resistor and take the output voltage from between the resistors. For input voltages up to 1V, the diode does not conduct, so Vout = Vin. For input voltages above 1V (really about 1.6V), the diode conducts and the input voltage is divided across the two resistors. At that point Vout = Vin/2 + 1.6V. You can see that if you do this in two or three stages and use the correct resistor values and voltages you will eventually round the peaks of the triangle wave to make a sinewave.

This is what Davood is suggesting. Hope that helps...

 

[seadolphine2000]

icl8038 price

Thanks to all of you,

Another thought, you can use a sinewave oscillator (usually one opamp or transistor plus band pass filter in closed loop configuration).

Then, you can use a comparator to convert to squarewave and an integrator to convert the squarewave to a triangle wave....

I've built this before and it worked good.

This sounds good, I think I'll do it like this BUT, What about the dealy of this circuit.??
i.e: The triangular is the 3rd stage after the sinusoidal and the square.
Does this affects the output frequency.???


Thanks again to all of you.

 

[jonw0224]

diode sine converter triangle

Mine was a Wien bridge oscillator to generate a sinewave. The square wave is "in phase" with the sinusoidal (except for time to switch the comparator), and the triangle wave reaches its peak at the transistion point of the square wave from "high to low". Therefore, the sinewave and the triangle wave are out of phase. The sinewave leads the triangle wave by 90 degrees. At 1 Mhz you need to be careful not to exceed the opamp slew rate and bandwidth (a 741 will not work!).

Again, the disadvantage is this: to change frequencies you have to change two resistors or two capacitors on the Wien bridge. In addition you have to change one resistor or one capacitor on the integrator (to get the slope right, so that the magnitude is the same at each frequency).

Another note about the Wien bridge, you want to drive it to oscillate but not overdrive it too much. Overdriving tends to distort the sinewave and increase THD.

Good luck

 

[seadolphine2000]

lm318 circuit

Thanks jonw0224,...

I'll use 3 LM339 or LM741 as the maximum frequency I can read on my homemade Scope is 200KHz.

I'm simulating the whole circuit now using OrCAD Pspice.

Is the LM339 works instead of LM741.???

 

[ace1903]

waveform generators with lm741+disadvantages

You should try to obtain ad9835. It is dds chip plus fout max =16MHz , all in one package for good price.

 

[rkodaira]

old function generator specs

Hi !

Answering your doubt: I think you cannot use LM339 as Op Amp in the sinewave oscillator, because LM339 is a comparator IC (suitable for squarewave oscillators). LM741 is a very limited Op Amp, although it can be used in the Wien Bridge Oscillator as Jonw have suggested.

The problem with Op Amp Wien Bridge oscillator is the limited bandwidth (no more than the audio frequency range) the necessity for a precision two gang potentiometer (because if you want variable frequency, both arms of the bridge should change equally in resistance) and the high starting feedback gain to start the oscillations and stabilization after output signal reaches the desired level (it can be made with fet transistors or diodes in antiparallel or even a small lamp in the feedback loop).

Of course you need symmetrical power supply to Op Amp (but you need it the same way if you are going to use the function generator ICs as MAX038 - the best, XR2206, ICL8038).

If built well, the wien bridge sinewave oscillator may have a low harmonic distortion

 

[seadolphine2000]

xr2206+pspice

Thanks very much to all of you.

rkodaira,..

The frequency problem is solved by 3 switches, as the frequencies I want are 1KHz, 10KHz, 100KHz. These are reached by 3 equal feedback networks.

I'll use a homemade power supply +5 & -5 volts.

Any ideas about a replacement to the LM741.???

Thanks

 

[jonw0224]

sine wave shaping diodes

LM318? TL05x? TLE208x? You just need high gain-bandwidth and high slew rate for 1Mhz and 100kHz. 741 has limited gain bandwidth and slew rate, but will work for 1kHz and 10kHz.

 

[seadolphine2000]

built sawtooth dds

Hi again,..

Can anyone give me full details about how to convert square wave to sine without using tuning circuits.????

I'm facing problems with changing the sine wave oscillator frequency, that's why I'll start with the square wave and convert it to sine.

Thanks to all of you.