[Coco] IDE interfaces

Zippster zippster278 at gmail.com
Wed Mar 16 17:37:39 EDT 2016

Thanks for that link John.  That was an interesting read.

I had understood that the possible issue being talked about was galvanic corrosion,
which might cause a problem when using dissimilar metals as electrical contacts
in an electrolyte.  In a “dry” situation like we’ talking about (and this is noted in the paper)
the electrolyte would be humidity in the air condensing on the contacts.

I’m just not seeing the electrolyte being present unless you’re in a VERY humid environment.
And in the conclusion portion of the paper, their tests for gold on tin contacts showed no
evidence of galvanic corrosion (presumably in air).  Their final conclusion being that the
gold on tin connectors tested showed no corrosion and were acceptable for
use in consumer electronics.

If the connectors in the CoCo are indeed gold plated, then gold wold be ideal on the card edge.
If they aren’t, (or are and you use a tin card-edge) then the lack of an electrolyte would still seem
to indicate there wouldn’t be a problem except maybe in super-humid environments.

It would seem to me all this that normal oxidation on the tin surface (as in storage or just sitting there), which
doesn’t happen with gold (by itself) would probably outweigh any galvanic effects, and even that would take
quite a while to happen.

The way I look at it is it’s probably just fine either way (at least until normal oxidation affects the tin),
but gold plating is a step up, especially long-term.

Interesting topic.   :)

- Ed

> On Mar 16, 2016, at 3:10 PM, John W. Linville <linville at tuxdriver.com> wrote:
> There are some papers out there on the topic...
> 	http://www.jsbtech.com/download/Effects%20of%20Galvanic%20Corrosion%20on%20Au-Sn-Plated%20Contacts.pdf
> I'm not much of a chemist, so I'm not prepared to render a verdict.
> John
> P.S.  I also view "always use gold contacts" with skepticism,
> especially for hobby projects...
> On Wed, Mar 16, 2016 at 02:40:39PM -0500, Dave Philipsen wrote:
>> I wholeheartedly agree with you.  It would take a lot of convincing to make
>> me believe that gold edge connectors are going to wear out the cart port
>> more quickly.  And almost all manufacturers of electrical connectors offer
>> gold-plating as a means of making the connection more reliable.  I remember
>> many years ago running my fingers across the contacts of those cheapo
>> cartridges and getting a grey-colored stain on my fingers from the
>> corrosion.  I've worn a gold-alloyed wedding ring for years and never had
>> any kind of stain on my fingers from it.
>> My question to the Facebooksters would be: Why did Intel use gold plating on
>> millions if not billions of their processors that were intended to mate with
>> sockets?  Perhaps they could do a little research on galvanic corrosion and
>> the anodic index of tin https://en.wikipedia.org/wiki/Galvanic_corrosion. An
>> inspection of the edge connectors on three of my CoCo 3s reveals that they
>> all appear to have some amount of gold on the contacts. At least Tandy got
>> that part right.
>> Dave
>> On 3/16/2016 2:15 PM, Zippster wrote:
>>> Gold edge connectors are bad, haven’t you heard?
>>> Just kidding, but there’s been a small discussion on the Facebook group where it’s being claimed
>>> tin-plated is better and won’t wear out your CoCo’s cart port connector as quickly as gold.  And that
>>> that is why Tandy didn’t use it most of the time, not because of cost.
>>> Personally I don’t  buy it, I think gold plated edge connectors are the way to go, even though they
>>> cost a bit more.  You can certainly argue it’s not necessary, but worse?  lol.
>>> - Ed
>>>> On Mar 16, 2016, at 1:47 PM, Dave Philipsen <dave at davebiz.com> wrote:
>>>> One thing I noticed about the MiniIDE is that there is no gold on the edge connector.  This is a mistake that shouldn't be repeated if someone decides to design a replacement.
>>>> Dave
>>>> On 3/15/2016 6:28 PM, RETRO Innovations wrote:
>>>>> It'd be interesting to see how small one could make the interface. If one used a flash ROM IC and a CPLD, I think one could put an IDE controller with IDE and CF into a 2.2"x2" form factor.  That's be small enough for any use, no?
>>>>> JIm
>>>>> On 3/15/2016 12:51 PM, Tormod Volden wrote:
>>>>>> On Tue, Mar 15, 2016 at 5:29 PM, Bill Pierce wrote:
>>>>>>> Some of the Brazillian Coco guys used the schematic from the Glenside unit and made a more "modern" solution that was smaller wih less parts (and fit the slot better). Maybe we could talk them into letting go of the schematic and get Ed to whip some up :-)
>>>>>> Here are some pictures of both the original Glenside board and the
>>>>>> Brazilian "MiniIDE": http://amxproject.com/?p=2585
>>>>>> Some people would probably prefer the big original with "integrated
>>>>>> MPI" and DIP40 chips, but I'd also be interested in the MiniIDE. Or
>>>>>> even a CPLD-based remake...
>>>>>> Tormod
>>>> -- 
>>>> Coco mailing list
>>>> Coco at maltedmedia.com
>>>> https://pairlist5.pair.net/mailman/listinfo/coco
>> -- 
>> Coco mailing list
>> Coco at maltedmedia.com
>> https://pairlist5.pair.net/mailman/listinfo/coco
> -- 
> John W. Linville		Someday the world will need a hero, and you
> linville at tuxdriver.com			might be all we have.  Be ready.
> -- 
> Coco mailing list
> Coco at maltedmedia.com
> https://pairlist5.pair.net/mailman/listinfo/coco

More information about the Coco mailing list