Functional Generator Question

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dave8976
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Functional Generator Question

Post by dave8976 » Sat Aug 16, 2003 5:39 pm

Has anyone ever thought of building a functional generator that produces sinewave, squarewave & triangle wave signals over a range of 1Hz to 20kHz or hgiher. I came across one design using the MAX038 (Maxim)chip. This chip also provide a TTL signal which make it easy to add an 8 digit frequency meter read out circuit instead of using an external frequency meter or a scope. Maybe this would be a good project constuction article in Nuts & Volts. The other choice would be to buy a functional generator - but one would miss the fun of building one.

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Chris Smith
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Re: Functional Generator Question

Post by Chris Smith » Sat Aug 16, 2003 5:48 pm

The 555 does this all. Over the years, we have all built the 555 in one form or the other. With different out put couplings, the 555 does the square, [a cap] triangle and with a transformer, even the sine wave.

Chris Foley
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Re: Functional Generator Question

Post by Chris Foley » Sun Aug 17, 2003 8:32 am

Somebody has already thought of your idea. You could do worse than the MAX038 kit based on the Electronics Australia August 1996 article. DIY 101 includes absolutely everything you need to make what you want, including plastic case. It's available for 75 bucks or so from a number of sources, including A1 Electronics.
http://www.a1parts.com/newkits/
You also might want to check out the Intersil 8038, which covers a higher frequency range (below 1 Hz to 300 KHz)
http://www.intersil.com/design/parametr ... pn=ICL8038
Jameco Electronics sells a basic kit (components, PCB, docs) for $24.95 as P/N 20685.<p>[ August 17, 2003: Message edited by: Chris Foley ]</p>

Dean Huster
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Re: Functional Generator Question

Post by Dean Huster » Sun Aug 17, 2003 3:38 pm

The MAX038 ain't no rinky-dink 20KHz chip. It's a full-fledged honey capable of 20MHz operation with all three waveforms. You can get lower-grade versions of the chip as a free engineering sample from Maxim (sometimes you can get the super-grade version, too) if you talk nice and look professional to them. However, the MAX038 is a picky chip and needs lots of good design with power supply decoupling and stuff like that or it will oscillate all over the place where you don't want it to or exhibit other nasty characteristics.<p>The Intersil 8038 is an easier chip to work with for such designs and there have been scores of those designs that have appeared in various places.<p>If you don't need the sine wave (most sine wave uses are nicer if they have low distortion such as from a Wein bridge oscillator anyway), you can use a Signetics 566 (National LM566) 8-pin function generator chip. There are also a couple of Exar FG chips available, but a bit harder to find.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

dave8976
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Re: Functional Generator Question

Post by dave8976 » Mon Aug 18, 2003 4:55 pm

Thank you for your comments. While searching for a functional generator schematic I came across the kit #101 as well as the original article as you mentioned Chris. I was not too sure if there were another choices of chips that could be used for this and was not aware of the Intersel one. I may have short changed the capabilities of the MAX038 chip as its upper frequency is 20Mhz and not 20khz as noted in my earlier note. - Dave

ajc-28
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Re: Functional Generator Question

Post by ajc-28 » Thu Aug 21, 2003 3:07 pm

The July 2000 issue of Nuts and Volts carried my construction article using a MAX038 chip as a low cost function generator. PC boards are still available.

dave8976
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Re: Functional Generator Question

Post by dave8976 » Fri Aug 22, 2003 2:11 pm

My suggestion of building a function generator came about while I was repairing my old Heathkit sine-square wave generator (1G-18). I got it working and calibrated. But I still think it would be handy having a functional generator with a digital freq read out. The Max038 chip does have a TTL output. My thoughts are to use this to drive a digital frequency meter circuit and package this in the same box. Can anyone suggest a good chip set to use to capture and display the frequency information. My thoughts are that teh read out would automatically show the correct freq information as I change or adjust the range. Thank you Dave

Bernius1
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Re: Functional Generator Question

Post by Bernius1 » Sat Aug 23, 2003 6:01 am

I'm doing about the same thing, but with the NE566. I plan on tapping off the output, floating it above ground, and feeding thru a comparator, and then to a D- or R/S flip-flop, then to a divider. Today, you can get 4-digit displays pre-wired for BCD, so the convertor chip isn't needed. But I have a bad feeling that when the output goes neg. with reference to the comparator's input, I'll be smelling smoke. One hour with the pen is better than two with the soldering iron.
Can't we end all posts with a comical quip?

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Re: Functional Generator Question

Post by chessman » Tue Aug 26, 2003 11:22 am

I agree the MAX038 is a little overkill for your application.<p>It's like using a shotgun to kill a snail

dave8976
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Re: Functional Generator Question

Post by dave8976 » Sat Aug 30, 2003 8:44 am

Based on further investigation and product review, I being to think that it is better to purchase a functional generator rather than to build one. Bu the time one adds up the cost of the circuit components, knobs, switches and housing, the price starts to get close to a commerical ready unit. This is one thing that I have noticed over the years that the choice of already built units are available and defeats the value of building something from scratch unless it is unique. Dave

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