macOS Custom PCBs and software

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There are a bunch of us hardware types around here. Can you describe the project a bit more?

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chown33 said:

All the parts I've ever bought from Mouser (or Digikey, or others) have a downloadable datasheet. It's usually linked to from the Mouser part page. It will have all the measurements, pinouts, etc. If you don't know how to read a datasheet, you'll be in trouble.

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This. If you have a specific question, ask.

So all we know so far is that it is a board with several through hole discrete parts. Since you mention software there must also be a microcontroller or something like that on there. Is that also TH/DIP? (edit: or was that a reference to DipTrace?)

How big is the board? How many layers? What kind(s) of power (volts & amps)? How will it be mounted/packaged? ...

You haven't given us much to go on.

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A lot of components are of a standard size. Dig through the standard Eagle libraries and find your components, then look at the specs and datasheets to verify they match. Eagle also is pretty good about showing you sizes on the screen, and I'm pretty sure you can print the layout to paper to see if your components fit. Not to sound rude, but I think you may be making it harder than it is.

Another thing that helps me when tracking down a component in Eagle is to download an Eagle library from one of the smaller distributors. Sparkfun and Adafruit both have libraries that pare down the choices, and most times the components you will use for all but the most obscure parts will be listed there. And remember, there are standard size packages for a reason. A 14 pin DIP is a 14 pin DIP, no matter what the IC is doing.

As far as placing the parts on a PCB, that is an art and not a science. (Well, there is *some* science...) I take inspiration from other boards--I lay things out after looking at other PCBs, just to see how they did it. And when it comes time for the traces, I straight out cheat. Auto-route. That gives me a starting point. It's nothing to go back and change things up a bit if needed. All that being said, everything I've done is pretty drop-dead simple, so this advice may not translate to more complicated layouts.

Good luck! It was/is sometimes very intimidating. I just think about it this way: I'm prototyping. Prototypes are never right the first time (unless you are insanely lucky or again, super simple). Learn more each time you do it and keep up the fight!

Sdashiki said:

Ive got a board laid out, but finding the real world parts to match the spacing and size...how!? Maybe I am thinking too hard.

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That's because you're doing it backwards. Select the parts then make the layout fit the parts you have identified.

From the sound of it you are looking at this as a 1 or 2 (metal) layer board. This might not be ideal. More layers can get you more flexible routing as well as better shielding. However a 2 layer board is probably fine for something this simple.

Have you identified a board house yet?

Frankly, I would not be surprised if you could not just use an SOIC version of the PIC on a proto board that allows for some passives around it. Schmartboard and Bellin Dynamic Systems (beldynsys.com) or Capital Advanced Technologies come to mind.

EDIT: I see part placement, but no routing in the pic you posted. Are you planning to route using wires? If not, you need to look at it with at least the "rats" which show connectivity turned on.

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Ok, so you are at what I would usually call initial part placement. You have a concept and need to select specific components to tweak your routing and placement.

This is where the art bit comes in as Thom_Edwards suggests.

The routing/wiring is the principal concern at layout, so hiding it doesn't do you any good.

Talk to a human at CustomPCB if you haven't already. My guess is that you can get 50-100 boards for a few bucks more than they would charge for 10. (I played with their online quote tool to verify this.)

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First question I'd ask is if you really need a custom PCB for this project. What's so special about this design that a general-purpose manufactured PIC prototyping board (with perhaps a few pads for customizations) wouldn't work?

You haven't stated your background: software, hardware, how much analog/digital electronic knowledge?

I'm a software engineer with a lot of hardware exposure. So, I've done some circuit design and even layed out a couple of boards, in the "old days" using tape.

Hope this isn't too elementary, but without further details... (and will help others understand the conversation)...

The most simple boards can be done single-sided, all of the traces on one side. You would use jumper wires when traces have to cross.

Next step up is double-sided, which might or might not have plated through-holes. Without plated thru-holes, you need to solder components (or jumpers) on both sides of the board. Plated through-holes create jumpers between layers by literally plating the insides thru-holes.

Most commercial PCBs today are a minimum of 4 layers, with dedicated ground and power planes. It's desirable for ground and power traces to be as wide as possible. Dedicated planes give each the maximum possible surface area. (There are just little rings cut-out around thru-holes between different layers.)

The data sheets for your active components - especially processors - will typically include some specific layout advice. Areas of typical concern are power and ground connections, mixed analog/digital (keep them apart), shielding (again particularly with analog/digital - for example, you might be told to place a shield in a specific place under a chip), and clock/oscillator connections.

Sdashiki said:

Cost is not the factor, its waste.

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Surprisingly waste is usually the reason why getting more is cheaper per unit.

Many fabrication houses will fab a whole panel no matter how many circuits you ask for. i.e. they will either make 100 of your little board just to sell you 5-10, because it fits their process better to handle a full panel (panels are typically somewhere in the letter to ledger page size range). Or they will leave the rest of the panel unprocessed and throw it away (less likely).

This may not be the case with custompcb, but it has been a real issue for me in the past. If they are really set up for low volume they may bundle your job with others to take better advantage of the raw materials, but I'm sure they won't be processing each one of your tiny boards individually. They will be arrayed somehow and processed together.

It would have been helpful if you had given all of the context up front rather than having to pull it out of you step by step.

Everything here is a trade. Since your external interface (the solder pads on the edges) do not appear to be through-hole, you might have made the choice to skip the holes altogether and using SMT parts (SOIC for the PIC and say 1206 for the discrete components so as not to make it too hard to hand solder). The board is easier to make (no holes to line up with the metal) and in many cases the components are actually cheaper, smaller (i.e. easier to route) and more readily available than through-hole parts these days

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Sdashiki said:

If I have solder pads, having through hole would be an extra step in the manufacturing process which just makes the whole thing more complicated for me to design in Eagle, correct?

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There should be a footprint for a solder pad with a through-hole that should already exist or you should be able to make one so that it doesn't impact things on your end.

Sdashiki said:

The price given was based on the size of the PCB, didnt care what went on it apparently. So SMD or not, it doesnt seem to change the pricing.

Now pricing of the components and overall size of the package in the end does matter...but I suppose we are talking pennies (1/8 axial vs 1206). And as long as this stuff does fit to the size I need, perhaps going SMD will be after this small run.

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This probably implies that it is largely automated.

What I'm seeing for a lot of components I want to use in designs is that the parts just aren't readily available in DIP anymore.

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Generally your next step is to generate Gerber files.

There, all the metal on Layer 1 should be one color at that point and a separate file is generated for your solder mask, and yet another for silk screen, and yet another for the drill instructions (locations, sizes)

The relationships between all of these is defined in your component footprints, but you should check the Gerbers too since that is what actually gets "printed".

In the old days we would actually print them on acetate and overlay them for final checks. Glad we can do that electronically now.

Edit: is there any current flowing in this circuit? The traces (wires) look mighty fine. I would tend to fatten them up and use shapes where possible. Also even for a simple board like this I'd tend to use the back side as ground and do a ground fill on the front side.

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I was staring at it a bit more.

Is there an easy way you could do a pin swap in your resistor array to avoid the route by "C" it looks like the three pads go to resistors just to the right of the pad. If those could be straightened you could get a nice direct shot.

I agree with chown33 that the thin routes near the edge and between pads are a liability.

Alternatively some of the routes you have as narrow lines near the edge could be moved to the backside with vias.

Edit: that's what I get for reading on my phone. I didn't notice you already had blue traces on the back.


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I'm partial to more ground fill rather than less. Unless there is a reason not to...

Are the "solder pads" at the top part of a card edge connector that handles both electrical and mechanical connection?

Are you going to program the PIC offline?

I'm still on my phone so will reserve further comment until I am on a real computer.

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