Mini DIY signal generator

[merlinb]

I've placed a 220k resistor in place of that capacitor, it doesn't work fine anyway...
Can anyone help me?

You don't need capacitor C3, it is optional. (But do not replace it with a resistor).

Does the circuit produce a sine wave?

[akkar]

yes, but no traces of the square wave... I've made a PCB but some trace were undivided so I've manually divided them with a cutter.. maybe the space between them is not enough (even though they now are not electrically connected).
is the circuit sensitive to this problem?

PS.sorry for my bad english

[merlinb]

yes, but no traces of the square wave... I've made a PCB but some trace were undivided so I've manually divided them with a cutter.. maybe the space between them is not enough (even though they now are not electrically connected).
is the circuit sensitive to this problem?

The circuit does not require wide space between traces, so I do not think that is the problem. Are you sure your layout / pin connections are correct?

[PRR]

> the Schmitt trigger doesn't need a resistor

There's no Schmitt in Merlin's post #7.

The square-wave is a plain comparator. That will work.

> doesn't work...

Explain. No output at all? Sine but no square? Sine isn't sine? Plays radio stations?

Review the DEBUGGING POST. Since Merlin's plan uses both + and - 9V power (did you use two batteries?), we expect IC pins to be +9V, -9V, or very nearly zero on the DC meter. Anything else is A Clue.

[akkar]

Like I've said there's no square wave at all.
the sine wave is present, but it tend to modify its shape
Anyway the +9V -9V supply is present on the respective ic's pins..

I think there's some problem in the copper traces or in the soldered pins

This is the pcb:

[merlinb]

I can't see anything wrong with the layout, so I guess it is a physical problem. (Wrong part / faulty part / short between tracks, etc.)

[akkar]

i'll make a new board when I have some free time..
thank you for your patience and help!

[tubelectron]

Hi all,

Just for fun and nothing else : here's my "Maxi non-DIY signal generator from the paleozoic era" (1959 laboratory grade / 23 tubes / 22kg) way to big for matchbox casing...



More seriously, for a simple DIY 20Hz-20KHz generator, the XR2206 or ICL8038 can work without too much components and give constant output voltage both in sine and square waves. Over this limit, the simplicity vanishes...

A+!

[Skruffyhound]

That's beautiful Bruno, I've been looking for something similar that will fit with the rest of my ancient analog junk.

Sorry to continue the hijack everyone.

Do you have a good circuit/pcb layout for the XR2206. I've seen Walt's on the forum and the app notes, anything different? When you say "constant output voltage", what do you mean? Can't I vary the peak to peak?
It's quite a while since I looked at the app notes  , you just got me interested again. Thanks

[bacanador]

Last year I was looking for Function Generator IC's, and didn't find any, but a couple of months ago I searched again, and found the XR2006 at mouser

http://www.mouser.com/ProductDetail/Exar/XR2206CP-F/?qs=sGAEpiMZZMs2Wv7C45tVfBqaYo2KUdBB

I don't know if they stopped making them and they started making them again, but I bought a few just in case, and made my function generator almost the exact same circuit shown in the datasheet, the circuit was simple enough not to require a layout, I just put the stuff on there and worked.

[tubelectron]

That's beautiful Bruno, I've been looking for something similar that will fit with the rest of my ancient analog junk.

Sorry to continue the hijack everyone.

Do you have a good circuit/pcb layout for the XR2206. I've seen Walt's on the forum and the app notes, anything different? When you say "constant output voltage", what do you mean? Can't I vary the peak to peak?
It's quite a while since I looked at the app notes  , you just got me interested again. Thanks

Hi Skruffyhound,

I made some trials with the ICL8038 and the XR2206 to make a simple and reliable function generator, that is to say :
- giving constant output voltage amplitude no matter the frequency.
- giving acceptable THD, say 2%.
impossible mission for me - remember I am more qualified about tube gear !
the only thing I could release is a 0,1 to 30Hz ICL8038 generator feeding a L165 10W power amp IC that I use to run-in the new speakers and inspect cone/suspensions defects. Nothing more...
So - sorry - I do not have good things about a fair but simple audio generator with a positive experience.

I should say : do not waste much your time and buy one for cheap on eBay !

A+!

[merlinb]

Here is an improved audio signal generator based on my first posting. This one produces a low-distortion sine wave from about 20Hz to around 15kHz. Maximum output about 2.5Vp-p, constant to within 0.3dB. Distortion less than 0.5% in the higher range, reaching about 1.5% in the lowest range. Not a bad effort for one quad opamp and a single 9V battery.

Incidentally, any LDR should work providing it has a dark resistance in excess of 100k. Enjoy!

[defaced]

Found my next project.  I'm not a big fan of using my cell phone as a signal generator for my amp. 

[jimmybjj]

has anyone made a pcb layout for this yet? Thanks.

[defaced]

You rang?  Ok, so it's been a couple of months, but I finally got around to doing this.  This has been built and verified by me (ok, I haven't added the switch yet, but the highest range works, so I don't anticipate any issues).  The only change I made between Merlin's schematic and this one is the addition of C9, for on board filtering of the power supply if it's needed.  All part number/values/pinouts match the original schematic/vero layout.  The Eagle TL074 part doesn't use the same opamp identifications as Merlin's schematic (U1a, U1b, etc), so I decided to match the pinout on the vero to the pinout on the PCB.  There are a couple of tight areas on the layout, so I reduced the trace width locally as needed, but I had no issues etching this using the toner transfer method.  Board measures 2.05 inches (52mm) by 1.83 inches (46.5mm).  Center to center distance of the pots is 1.25 inches (31.75mm).  The trace side of the board is shown from like you're looking through the board, so get your toner transfer/photo supplies ready!  

I have also made a project PDF for this (think utilitarian version of madbean/tonepad docs). Might make printing the layout easier.  Merlin do you mind if I post it (assuming I can find a place to host it)?  Credit given, of course.  

[merlinb]

Merlin do you mind if I post it (assuming I can find a place to host it)?  Credit given, of course.

Be my guest!  

By the way, put some text on the board to avoid confusion over the orientation. I usually write on the board dimensions, so you can handily check both the print size and orientation.

[Perrow]

The trace side of the board is shown from like you're looking through the board, so toner transfer guys are ready to go, photo guys will need to mirror it.

No, no, no, photo guys print this way too. We just print this on a transparency and place it with the "ink side" against the board, this way the pattern gets as close as possible to the board 

[defaced]

Thanks Merlin, good suggestions, will do.

Parrow, makes perfect sense.  I'll update my post to reflect.  

[sliberty]

If anyone is making any of these PCB's, I'd really like to buy 2 of them from you. Please contact me (steve at sliberty dot com).

[merlinb]

Another PCB for the sig gen circuit. This one allows for up to four frequency ranges using a DP4T rotary switch, covering roughly 20Hz - 100kHz in total. This is the switch I used:
http://www.ebay.com/itm/2-Pole-4-Position-Panel-PCB-Wiring-Rotary-Switch-2P4T-/330588499247?pt=LH_DefaultDomain_0&hash=item4cf89c2d2fpt=UK_BOI_Electrical_Components_Supplies_ET&hash=item4cf8952614

Also added a power indicator LED (D5) and reverse protection for the main LED (D4). The frequency pot is arranged to increase the frequency when rotated anti-clockwise when mounted on the solder side, so that using a log pot gives a linear change in frequency.
http://s81.photobucket.com/albums/j207/merlinblencowe/Sine%20Wave%20Generator/