My latest PCB.

[Hero999]

Attached are some pictures of the PCB for a noise generator I'm currently building.

I used the toner transfer process with magazine paper. For the silk screen I covered the toner with a thin conformal coating to stop it from being scratched off.

It isn't perfect but it's good enough for me - the traces all etched perfectly which is the most important thing.

Although I've experimented with printing a silk screen before, this is the first time I've done it for real. As you can see it isn't perfect. The toner all stuck perfectly, but some bits came off when I cleaned it so I filled in the gaps with a permanent marker which ran when I sprayed on the conformal coating. The alignment also isn't perfect and there's some slight bleeding which I think could be caused by the temperature setting being too high.


I've learnt a couple s few things from this. Next time I'm going to be more careful cleaning it, I'll a pencil to do touch ups and iron using a slightly lower temperature setting.

View attachment 40611

View attachment 40612

 

[gogo2520]

Nice looking board Hero999 . You used conformal coating? I have a few ideas for my next board, Have you ever tried this stuff
http://www.web-tronics.com/torefowpwh.html
  I also have some small silk screen like stuff in small sheets that can be photo exposed, haven't tried that yet, think I am saving it for a real good board that I would want to reproduce in numbers.
http://www.photoezsilkscreen.com/howto-create.htm
  anyways, your boards look good
                                        Thanks for sharing
                                                gogo

 

[Hero999]

Yes, I've seen many proprietary silk screen products but I've never used them. They look nice but they're also more expensive than simple toner transfer. I think black is fine for a silk screen, it does the job and I've seen professional PCBs with a black silk screen.

Here's a link to the lacquer I use:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=569-290&x=0&y=0

My only concern is that it might not be resistant to isopropanol or acetone which I use to remove the solder flux from the board. I might have to switch to a solder with water soluble flux.

Here's a PDF of the schematic and PCB layout. I noticed an error in the PCB after etching the board, I forgot to connect the op-amp's 0V pin, the error has been corrected on the attached file.

Here's a link to where I borrowed the design for the low pass filter from
http://sound.westhost.com/project11.htm

Noise_generator.pdf

 

[Hero999]

I've assembled the PCB now.

I haven't tested it yet though.

View attachment 40619

 

[audioguru2]

I made my pink noise generator with a National Semi MM5837 psuedo-random digital noise generator IC (now it is obsolete). I used a few RC networks to convert the white noise into pink noise then I tweaked the values for it to match the output of a very expensive professional noise generator.