schematic to board advice

[tab a]

Having never done this before, I'm looking for some very general advice/guidelines/tips for placing components on a board. I've searched this site, and done some googling but haven't found much. Software that I THOUGHT might help all looked to be PC rather than MAC based?

I'm in the process of building Marvin Smith's In-circuit capacitor tester (Poptronics 2001), so have the schematic and parts (the board is a Radio Shack 276-150). I've breadboarded it just to get an idea where things might go, and have what looks like a pretty good mess! I could do it this way but suspect I'm missing some simple ideas that would clean it up considerably. I've got several electronic textbooks and troubleshooting books, and have repaired a few items but keep in mind I know little to nothing about this particular challenge--or most of electronics, for that matter.

Very much appreciate any thoughts you may have!

Thanks.

 

[dknguyen]

First things, first. Does the board work?

 

[hjames]

I don't know how complex the circuit is, so I can't give any specific recommendations, but in general:

If you have enough space, and there isn't a lot of distance critical wires, spread the circuit over the entire protoboard. Ideally label any important parts/wires.

Get some bare bus wire, or just some uninsulated solid wire for the ground/power lines. Just using properly sized jumper wires will cut down a lot of the clutter when compared to the breadboarded version.

Other than that, component placement is very unstructured - there are obviously many bad ways of orienting/organizing parts, but there are also many good ways, and there is very rarely a best way of doing it. It's more important to just get something that is "good enough", and leave it at that.

 

[tab a]

I didn't test the breadboard, since I 'know' the schematic works. I just wanted to get an idea of how all this would look on a first attempt. (The very faint/fuzzy pics in the article look like a work of art. Mine, not so much.)

I don't think the circuit is terribly complex--1 quad op-amp, 3 transistors, 22 resistors and a few caps, diodes, etc. I realize there is probably not a 'best' way, but was hoping there might be some general principles to follow. For instance, this board has 2 rows of connected holes running down the middle. I presumed it would be a good idea to use those for the multiple components that need to go to ground. Now after looking at it, I'm thinking that may not be the best use of space. I know that with my level of expertise, sometimes what seems like common sense, isn't.

Perhaps another way to ask the question is: When you go from a schematic to a board, do you just start plopping components down, from say, left to right on the schematic, and then moving them as the need arises, or do you instictively group some here and some there, connected with jumpers, or is it all simply a matter of trial and error, tempered by experience?

Thanks again.

 

[hjames]

The two rows running down the middle is pretty standard - most logic chips have the power and ground pins laid out consistently and are very easy to wire up in this way. Analog circuits tend to be a lot less structured.

Keep in mind that you can always cut up the traces, and run short wires on the "solder side" to keep the top of the board relatively clean.

One big thing that drives component placement is input/output connections. Figure out how/where you want to connect this circuit to the outside world, and arrange the parts accordingly. It's also nice to "follow" the schematic's grouping as much as possible - it makes it easier to figure things out later, especially if all this is done by hand. Also, you'll probably also want to either draw the parts placement by hand, or get a simple PCB layout program (there's a handful of free ones floating around, search the forums) to document how you've connected all the pins together.

Keep in mind that breadboards are inherently "ugly" - they're supposed to be relatively quickly built, serve as one-off's, or at the most, prototypes for a real run of custom PCB's.

 

[Dean Huster]

The answer to this one is a lot easier than you might think. Marvin didn't publish a PCB layout for his "In-Circuit Capacitor Tester" in the July 2001 issue of Poptronics (pages 25 - 28), but in the interim, I made a layout and published it in my "Q&A" column in Poptronics (February 2002, pages 48 & 49) with a subsequent comment and update on that layout in the June 2002 installment of the column on page 52. If you don't have access to those issues (Poptronics and Gernsback went out of business in January of 2003), I'd be glad to scan the layout and send a copy to you. My e-mail address should be in my profile (left-click on my name).

Dean

 

[tab a]

Hjames et.al., thanks for the tips--very helpful!

I spent a couple of hours last night redoing it and it looks considerably better. I do have a couple more 'practical' questions though:

1. The maximum connected holes on my board is three (ignoring the center rows). It's not unusual to need to connect four different components. Do I need to jumper to an adjacent 3-way, or would it be acceptable to 'bridge' to an adjacent hole with just solder, or?

2. Most of the components end up being on one side of the 14 pin IC, or the other. There does need to be a resistor between pin 3 and 11, though. Would this commonly be accomplished by jumpering all the way around the IC, or, using the other side of the board, or?

Dean, I would appreciate a scan of the layout, primarily because I think it will now provide me with more than a few, "Aha, why didn't I think of that's". Thanks.

 

[Dean Huster]

Contact me via e-mail and I'll send you a jpeg version of the PCB layout and the parts placement diagram.

Dean

 

[hjames]

It's probably easier to bridge the round pads on the bottom of the board with a piece of uninsulated wire. Tack-solder one end of the wire into a hole, and run it along the bottom of the board, and solder it to whatever round pads you want connected together.

Jumpering around the part, and having all the parts on the topside of the board would be cleaner and easier to debug, but it does take up more space. It's your prototype, and your call. The utterly ugly way is to just run it above the IC, but that us usually only done when one is making a quick fix...

 

[tab a]

I realize there are lots of ways to do this. Just wanted to try to develop some good habits, rather than bad ones.

Thanks.