Oh, use the grid, in both the schematic and the board.

In the schematic capture, I almost always have it set to 0.1 inch; not much reason to change it.

In board layout, I start with it set to 0.1" to see how things are aligned. The board is always slightly oversized when you start; hold down the Ctrl button and left-click each corner to "snap" it to the grid.

If parts are not aligned to the grid, I might reduce to 0.05" to get things lined up, and when running traces between the pins of IC's.

Don't turn the grid off, or go exceedingly fine unnecessarily, or you will wind up with a mess.

 

It just seems that they will attach to say the correct vcc pin, but rather than the gnd pin of the ic, to the closest pin i'm taking low for signal reasons, i.e. the clock inhibit pin.

I see. That's OK, just put the caps as close as you can to both the GND and VCC pins, and run traces straight to them.

Still sifting though the erc and interpreting the errors, I see what you mean about using early and often!

Yes, errors accumulate very quickly. Much easier to handle a few at a time rather than a huge list.

Junctions: (schematic capture) if two wires intersect, you must have a junction placed on top of them to connect them. If you later add yet another wire to the junction, you must delete the original junction symbol and place a new one. You don't have to use a junction when connecting to an IC pin, but sometimes a connection won't "take"; I'll usually just move an IC slightly out of position and then back to get the wires to connect to the pins.

Wires won't always connect if you've run them separately, even though they look like they're touching. Usually just dropping a junction on top of where they butt together and deleting the junction takes care of it.

 

I see. That's OK, just put the caps as close as you can to both the GND and VCC pins, and run traces straight to them.

Awww man! You mean I can't just hit auto route? I have to do some work?



Sol

 

Autoroute is OK for some things, but you can get into trouble with having signals routed too close together, and winding up with noise coupled from one trace to another.

 

In that case I think I need to find a "best practices" guide on how to rute it by hand, up to now I have mainly used auto route :s

Sol

 

Here: http://www.smps.us/pcb-design.html
Lots of info and various calculators.

Sparkfun has a pretty decent tutorial on Cadsoft Eagle. Have a look:
http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=108

 

Here's an intro to PCB design that's easy to read with some illustrations:
http://www.alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

 

With the input pins in wanting to be low, currently I have connected them to ground. Is that enough or do I need to use a pull down resistor ( first thing that came to mind ) or is just being connected to ground?

Thanks

Sol

 

With the input pins in wanting to be low, currently I have connected them to ground. Is that enough or do I need to use a pull down resistor ( first thing that came to mind ) or is just being connected to ground?

Sol,
Sorry it took so long for a reply; I just got back in from being out of town.

In your schematic, you show the inputs to IC1-IC3 having 50k Ohm pull-down resistor networks, not connected directly to ground.

If you DID connect the IC1-IC3 inputs directly to ground, IC4-IC6 would not be able to raise the inputs to a logic 1; any cable you tested would look like it was open, and the high current levels from IC4-IC6 through the cable to ground would likely damage their outputs.

 

aah, I should have explained better. I meant pins like, clock inhibit or serial in. Pins I want to set to low permanently in my schematic.

Hope your trip was fun!

Sol

 

aah, I should have explained better. I meant pins like, clock inhibit or serial in. Pins I want to set to low permanently in my schematic.

Oh, OK. Sure, ground those.

 

Great, thanks, I just wasn't sure that if I also connected an output to ground that went high that it might effect an input also connected to ground that should be low.

Sol

 

No, you should not connect OUTPUTS to ground; only INPUTS.
If you connect any OUTPUTS directly to ground, you will have problems.

 

All changed, I see now I shouldn't have done that :s

Looking at the schematic, the power cable that is will be testing could be incorrectly connected to the mains *150-250v* by user error, that being one end to mains power and the other to the tester, rather t5han both to the tester. This would be connected to IC 6-4. So, i'm thinking I could change my diodes to not just correct testing, but to prevent 240v getting to my ic's?

Just scratching my brain and reading up on what characteristic I need to change on my current diodes.

Sol

 

All changed, I see now I shouldn't have done that :s

Oh yes, you had the QH\ outputs tied to GND on IC1-IC3. Not good!

Looking at the schematic, the power cable that is will be testing could be incorrectly connected to the mains *150-250v* by user error. This would be connected to IC 6-4. So, i'm thinking I could change my diodes to not just correct testing, but to prevent 240v getting to my ic's?

You can't protect against complete foolishness by a user. You wouldn't be able to use diodes to protect it from that kind of error without preventing it from functioning at all - unless perhaps you used diodes with such limited current handling capacity that they would burn out before the IC outputs fried. Actually, it would be more like a small explosion; their lids would be blown clean off.

I suppose you could use resettable fuses like PPTC's, but that would add complexity and lots of cost. Cheaper to use IC sockets and keep spares around.