Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "kaytea2k" <kaytea2k@y...> 
wrote:
> I don't know what the problem is but I know that the design is 
> sound.  I have experience with design from the number of 
> electrical/electronic engineering courses I took in college.  
Though 
> EE is not my major I understand the components and how they work.  
> The schematic posted @ sanisis.netfirms.com is a schematic I redid 
> inorder to make it easier for a fabricator.
> 
> I have gone over the schematic here with some professional 
> fabricators and I am HERE trying to get you all to help.  Any 
poster 
> should know that a schematic should be tested and working.  I 
believe 
> once I have a layout and prototyped board then there should be no 
> problem as far as adding and removing.
> 
> If you have any constructive suggestions or are able to DO the work 
> then please reply to my e:mail.  kaytea2k@y...
> 
> Karega



Please don't take our conversation as criticism.  If you review the 
posts, we chat about things all the time and stray from the topic 
with a little energy to keeping it generally about electronics and 
making boards.

The schematic is a very general outline.  
http://sanisis.netfirms.com/

The are no notations on the caps on the power supply.  probably 
0.01uf or 0.1uf, 

all resistors could be 1/4 watt

no spec for the diode

RX433 is not a standard part, but a part in kit form.  there are a 
few variations on that part.  

No antenna connection device is listed.

The 555 capacitor is not listed for pin spacing, it could be 100 mil 
or 400 mil as different caps have hugely different pin spacing.

The transistors for the LEDs are not called out, they are probably 
TO92 case, but are the EBC, BCE, ??

Power connections are not called out, are they solder pads for wires 
or spacing for screw terminals or pins for a Molex or other ?
if screw terminals, are they 100mil ? 3.5mm ? 5 mm ? 5.09mm ? 3/8 
inch?

A lot of people tie MCLR to Vcc with a 4.7k or 10k and not 100k to 
ground.

There is no ISCP listed, so the PIC would need to be pulled for 
programming.

I'm not saying that we can't do such a board, but that with roughly 
140 holes there would be 20 mil for resistors and caps, 29 for the 
DIPs, something for the connectors, and something for the antenna.

The only way most of us would consider making such a board is if we 
had all the parts to measure or if all the parts were fully listed on 
the schematic.

For example, I just made a board for a customer and the manufacture 
of the switches gave me physical dimmentions for the pins and 
electrical connections.  Only problem is that the information was 
wrong.  on a switch pins 1 and 3 were common when pins 1 and 2 were 
listed as common.  instant short.  required modification of the 
board.  Luckily, the customer gave me the data from the 
manufacturer.  Customers are sooo much more understanding when they 
make the mistakes.

It may be a simple matter to download ExpressPCB and use that free 
layout software, or WinQCad as that is free and has a very shallow 
learning curve.


Please understand that making a board requires multiple layers.

The most general is done, your schematic.

next is parts selection followed by the math for verification that 
the ranges are compatible.

Next is re-selection of parts as needed followed by manufacture or 
supplier part numbers.

that is followed by package physical dimensions, hole sizes, pin 
spacing clearance around parts for heat, ventilation, connection, 
clearance etc.

then the board can be laid out with hopes that there are no 
mistakes.  A TO-92 BEC may be purchased when a EBC was laid out.  
requires some attention when stuffing the board.  ie: my switch 
problem.

Then of course, there is the final step of making sure it will fit an 
enclosure or housing, and that it has holes for mounting.

I didn't take the time to write this to make fun, but to try to 
convey that it looks really really simple, but this is one area of 
endeavors where the devil is in the details.

Electrical spec details
connection details
physical layout details
and physical properties details.

All those have to be 100% compatible or the thing won't work.

I listed enough questions that would prevent me from making such a 
board from this schematic and I bypassed some of the more obvious 
ones in case others want to point out some of the missed requirements.

But, I can say with total certainty, that the board as laid out with 
the parts listed in the schematic will not work.  There is at least 
one flaw that will prevent proper operation.

Dave