Low-Cost Function Generator

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[Ideas For Design]
Low-Cost Function Generator

Ken Levine | ED Online ID #1371 | April 3, 2000

This low-cost function generator, based on the Maxim MAX038 high-frequency waveform generator, produces sine, triangle, and square waves from under 1 Hz to over 20 MHz (see the figure). The frequency, amplitude, and offset of all output waveforms are adjustable, as is the duty cycle of the square wave.

Frequency adjustment is accomplished with a capacitor bank and a variable resistor. Amplitude, offset, and duty-cycle adjustments are performed via variable resistors. Switches S2 and S3 select the waveform type to be generated. The frequency range is chosen using one of 12 capacitors, C2-C13, via switch S4. Resistor R16 is for fine-tuning. The f_ADJ pin of U1 is tied to ground through a 12k resistor, so the frequency of the waveform at U1-19 is f = 2(I_IN/C_F), where I_IN = V_REF/R, R is the sum of R7 and R16, and V_REF = 2.5 V. The values of C2-C13, R16, and R7 were chosen to provide frequency-range overlap. Table 1 shows the frequency range for each capacitor value.

The output at U1-19 is 2 V p-p, centered around zero, for all waveforms. For amplitude adjustment, R18 and R9 form a voltage divider. The portion of U1-19 fed to the summing amplifier U3 varies from 0.74% to 100%. The summing amplifier multiplies this voltage by −12.2, so the signal at U3-6 will vary from 0.18 V p-p to 24.4 V p-p.

The offset voltage is controlled by resistor R15. This voltage is fed to the summing amplifier, where it's added directly (the gain through the summing amp is −1) to the waveform voltage. Resistors R1 and R2 force the variation in the offset voltage to be within −13.6 V to +13.6 V to prevent the unity-gain buffer amplifier from being overdriven.

Duty-cycle adjustment is controlled by resistor R17. The +2.5-V reference voltage of U1 is passed through a unity-gain inverter to R5. R5, R17, and R6 (which is tied to the +2.5-V reference voltage) form a voltage divider. The voltage developed across R17 varies from −2.3 V to +2.3 V. It first goes through a unity-gain buffer, then to the D_ADJ pin of U1. This ensures that the voltage at D_ADJfalls within the operating limits of −2.3 V to +2.3 V.

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Reader Comments

Hey I'm very interested in making a frequency generator i=I need one for my project. I was wondering if it was possible if I could get a clear circuit diagram from you in bmp format or rar'd bmp if possible. If anyone still has trouble finding the max038 chip I managed to find a supplier that doesn't have rohs certified versions but I don't mind if it does or doesn't have lead my solder has lead in it anyways. Thanks in advance. bonze82athotmaildotcom

Anonymous -November 17, 2008

I am working on a project, that needs a function generator that will go to a audio amplifier. Then from the audio amplifier to piezoeelectric drive transducers. Any help wound be appreciated.

Thanks,

Doug -October 22, 2008

hi i m making a project on function generator so can u please tel me its relevant theory or information from starting to end.

Anonymous -July 25, 2008

hi i need to design a high frequency function generator. if u can please mail you'r board schematic for me best regards

Anonymous -May 10, 2008

dear sir or mam,i am doing a project(the pic gene function generator/counter) and i need to know the operation,from start to end. May you please help?

kitah -May 09, 2008

Hi, I am currently in the process of designing a function generator for a project and looking for some help and advice, If anybody could help with either information, websites or similar designs on the net i can work from this would be muchly appreciated. The Basic requirements are: • Operate at 12v d.c • Have an output amplitude between 100mV-1V • Operate between frequency range 50-50kHz • A means of selecting Sine or Square wave outputs • A means of selecting the frequency

Please email if you can help.

Regards

Scott

Scott -March 10, 2008

How can i add a 3 phase outpot to generator?thanks

wetsu1 -March 04, 2008

Great design, please let me know: 1. If you can recommend a replacement for the MAX038? 2. Are all op amps the LM324? Thanks

Cork -January 17, 2008

hi I would like to know where I can buy this component.. Thanks for your help I expect a prompt response

pieru -January 16, 2008

hi I would like to know where I can buy this component.. Thanks for your help I expect a prompt response

pieru -January 16, 2008

Does anyone know if anyone is making a comparable chip to the MAX038? As Bambos Charalambous noted, the chip is now discontinued and somewhat hard to find.

Anonymous -December 21, 2007

Where I can buy the chip??

George -September 02, 2007

Hi sir, may I know how you derive the formula to calculate the frequency of the waveforms? (f = 2(IIN/CF)) I am doing a project and wish that I can get some useful sources from you. Please email me with some related information about funtion generator. Thanks.

Chinnie -April 18, 2007 (Article Rating:

)

Neat project. Too bad the boneheads at Maxim just discontinued the max038. And there is no replacement. They do this sort of thing alot. If anyone knows a place where we can buy them in small quantities please post it here. Thanks

Anonymous -April 18, 2007

I’m studying computer engineering and I have been assigned to build a function generator with a frequency tuner for one of my projects. I found your article very useful. If you have any guide lines that could help me go through this project please e-mail me.

Lots of thanks,

Bambos Charalambous

Bambos Charalambous -March 05, 2007 (Article Rating:

)

Lots of thanks,

Bambos Charalambous

Bambos Charalambous -March 05, 2007 (Article Rating:

)

"Low-Cost Functional Generator"

When looking at the schematic, there is a IC that is not labeled. Top center of the schematic where the 15vdc input, each leg runs through 500 ohm resistors through a varible resistor past a 0.1 micrfran cap to a IC terminal #10. This IC is not identified. Can you give me the number for this IC?

Rick -January 19, 2007

one op-amp has no label...what op-amp is that

Anonymous -November 19, 2006

Hi this is interesting. Pls advice where can I find the PCB drawing of this function generator?

Ganesh -June 18, 2006 (Article Rating:

)

Pls, I am final year student of electronics engineering and I have to design and construct a function generator with at least 4 waveforms and the output should be displayed on oscilloscope .It should also include a variable duty cycle and modulation capabilities.Pls how can I go about this project.I need a detailed documentation on this subject with strong design process and construction details.

Anonymous -May 25, 2006

Hi. I'm a electronic student and i have to make a digital fuction generator for my final project. I have to switch the wave forms, the amplitude and de frequency by programming an 8051 microprocessor with a keypad and a LCD to make the interface with the oscilator trough a DAC. Can you tell me if there is any web site, book or any other source where i can get documentation on this subject? Best regards.

Anonymous -December 19, 2005 (Article Rating:

)

i saw your design and it is very nice and simple. may i know which ic is op37 and what is the Ic number which is just behind op37. thank you

Anonymous -December 13, 2005 (Article Rating:

)

Hi Dear Sir or Lady I need circuit for communications on power line thanks and my best regards

Mehdi -December 04, 2005

Nice function generator design. Mine is not finished yet, but the design looks great. No pc board layout is available (asked the author) - trying to create one myself (not too easy, I think). What about the opamps slew rate? Do you have any hints for a better substitute?

Frederik Suhr -October 31, 2005 (Article Rating:

)

Hi. Very nice article. Where can I find the PCB foil pattern & PCB silk screen of this function generator? Best regards.

Vijay -September 18, 2005 (Article Rating:

)

hello sir i find your article very nice.i wan't to design a fg for a project can you please help me

anant -September 16, 2005 (Article Rating:

)

Nice little project. I agree with the other comment about the OP37 (The slew rate is too low) for a decent output signal. Also you need to be careful with grounds and wiring if you want a handwired version to make it to 20MHz. The phase noise/jitter was high at high frequencies. The one reader who wanted a digital display can find a synthesized version using the MAX38 on the MAX038 data sheet ( uses a MOTO PLL chip ) but the wiring is much more complicated and you'll need a PIC. Thats my next project!!

Jeff Meyer -July 30, 2005 (Article Rating:

)

please provide in the same generator with a digital display .prefferably through a 7 segment l.e.d

Anonymous -June 14, 2005

for my lab i am going to build this.some components values are not readable on my monitor i.e R3,R7,R8,R9,C3,C4.??? could i use capacitor =>1uf as 25v electrolytes? multiturn trim POTs will be ok?

Rehan -June 02, 2005 (Article Rating: