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Project Help and Ideas » IC sockets, PCBs, etc. for finished product

February 05, 2010
by iamtheari
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I am still designing my project, discussed here: http://www.nerdkits.com/forum/thread/363/

I am at the point where I want to start buying all the components to make it happen. But what I don't know about yet is how best to put together the circuit board for the finished product. I will have 2 ICs (28-pin Atmega168 and 20-pin relay driver) on one circuit board and 3 ICs (28-pin Atmega168, 20-pin relay driver, and 16-pin 8-to-3 encoder) on the other one. I could use long breadboards to prototype everything, but ideally I will solder things into a more permanent state at some point since the finished product will literally be stomped on when in use. :)

Does anyone have some advice for which way to go? Wire-wrap, custom PCBs, whatever else?

Also, for the stupid question portion of this broadcast, I'd like to ask if anyone knows what size/spacing IC socket to get for the Atmega168. Thanks. :)

February 05, 2010
by mongo
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Something I have lots of time with...

There are numerous printed circuit breadboards and the like on the market. My personal favorite is the type with nothing but plated-thru holes. A little more work in building things but can be compact as you want to get. There are some which resemble the same format as the little breadboard that comes with the NK if you aren't too concerned with space.

I would suggest avoiding wire wrapping. It's kinda expensive and not very forgiving.It also takes up more space.

Good quality IC sockets are widely available for all sizes of chips. In a pinch however, two 14 pin IC sockets can be set end to end to accommodate the 28 pin MCU's we use here.

I'll dig up some of my old projects over the years and take some pictures so the construction technique I use can be seen.

February 05, 2010
by iamtheari
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Thanks for the quick reply. I was shopping for 28-pin IC sockets and found a few, but they seem to come in more than one width and pin spacing combination. I am familiar with the PCBs you mentioned that are laid out similar to a breadboard and in fact probably have a small one somewhere from a previous (analog) project since they come in 2-packs from Radio Shack. I am not so familiar with the other kind you mentioned.

February 05, 2010
by mongo
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alt image text

Here we go,

An old project about 30 years ago. This is a logic probe of my own invention. It reads "H" for a logic high and "L" for a logic low. It reads "-" for open connections. It was built on plain perfboard and to save room, I wired things over and under the board. All point to point wiring. It's an early version but works beautifully. You can see a strip of plastic under some of the leads... It separates another one underneath so they don't touch.

Not the prettiest in the world but the IBM blue covers it up when the case is closed. It is powered directly from the +5V supply.

February 05, 2010
by iamtheari
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Cool, thanks. I can probably handle perfboard - as long as I know how to securely mount components to it. Just bend the leads back, solder, and trim?

February 05, 2010
by mongo
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Pretty much it!

I usually bent over one at opposite corners. Once things start getting connected, the little wires hold it in place. The wires in the pic are actually wire wrap leads, solid silver with blue insulation. It is really small wire gauge (28 I think) but 22 or 24 works well too. I save all of my resistor leads and clippings for the short ones so I don't have to cut anything into little pieces. A good soldering iron with a fine tip and small needle-nosed pliers are very nice for this little stuff. (Also helps you not burn the ol' fingers)

Some times, I have been known to super glue things in place as well. I also use sockets for some things, as I find it easier to replace chips that way when needed. Desoldering is an art form and unless you do a lot of it like I did back in the day, it is usually more damaging than helpful.

February 05, 2010
by iamtheari
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I'm paranoid enough to invest in IC sockets for every IC. That's not a concern. Plus, it makes reprogramming the MCU a lot easier since I can just pull it and put it in a programmer (which I may just have to build for myself, based on the NK general breadboard but hard-wired to work in USB programming mode.

What's a good source for perfboard? I've never bought it before and don't recall having seen it at Radio Shack.

February 05, 2010
by rajabalu21
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They are available with Radio Shack check here

-Raja

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