D connectors

[bobrayner]

This may sound a little picky but it doesn't hurt to get it right.
There has been considerable reference to "DB9" connectors such as the serial connector.
The correct terminology is "DE9". The first letter (D) referrs to the connector style, the second to the standard shell or body size, ie: E=9, A=15, B=25, C=37, D=50. Thus reference to "DB9" indicates a 25 pin shell size with 9 pins. This terminology became desirable with the introduction of high density connectors, for instance the video connector is a 15 pin in a 9 pin body style, it thus becomes a "DE15". Similarly we have a "DC62", "DD70" and so on.
Finally, "D" connectors have a finite life. From memory a better quality gold plated pin has a guaranteed life of only 50 insertions if flash plated and 200 insertions if a heavier gold finish is used (forget the actual gold thickness). Also rolled and machined pins differ in their lifespan.
The above information can be obtained from the "Connector Encyclopaedia" (which the average person is very unlikely to have access to, VERY VERY expensive)or detailed manufacturers specifications.
As the average hobyist probably uses the most economical connector he (or she)can get the possibility of some of the intermittent problems reported being due to a worn out "D" connector maybe should not be overlooked.
Cheers BobR

 

[Technical]

We do not recommend using a 9 pin D connector as the PICAXE download connector ever. As you suggest they have a very small number of mating cycles and can fail very quickly when repeatedly disconnected from a PICAXE circuit, particularly in the educational environment.

 

[hippy]

That's very interesting and informative, so thanks for both the technical details of connector type naming and the mating cycle information. I've been plugging DE9's in and out and swapping cables over quite merrily and very frequently without ever giving it a second thought.

Out of interest, and for comparison, on the mating cycle front -

* How do 3.5mm jacks / sockets rate ?

* How do the 3-pin molex plugs / sockets rate ?

Most of my projects involve multiple PICAXE's so download usually means moving the cable between every PICAXE for its own download. That obviously puts considerable strain on the connections. And I guess it's the same in an educational environment when students all use the same or a few computers to download from.

From my real world experiences, which may be meaningless in isolation - I've noticed no problem with switching DE9's, my 3-pin header socket can need waggling to make it work, I've had three 3.5mm sockets fail on various PC sound cards with very little mating cycling ( I've presumed cable weight tilts the jack and bends the internal contacts of the socket ).

 

[ylp88]

But doesn't Rev. Ed. sell a PICAXE download cable with a DE9 connector (almost put DB9) to 3.5mm stereo connector? Am I thinking straight?

ylp88

 

[hippy]

They do ( plus a DE9 to 3-pin molex cable ), but in most cases I guess it would be more likely that a user would only have a single cable and that it is the PICAXE end which would be more frequently plugged in and out rather than the DE9/PC connection.

The opposite could however be more true of a user working on a single project who was switching between PC's or laptops.

The warning is, don't fit a DE9 socket to your PICAXE board and use a DE9-DE9 cable for the download link, as the DE9 are only rated for a few mating cycles.

And implicitly also, don't unplug the DE9 of the approved download cables from the PC too often.

 

[Technical]

As with most comptuter cables, it is assumed that the computer end of the cable is usually left in place and the 'PICAXE hardware' end of the cable is the one that is moved back and forth.

It's also worth noting, particularly in the educational environemnt, that students tend to flex the PCB/connector solder joints much more with DE9 connectors, due to their larger physical size and hence 'leverage' potential. This can also rapidly lead to failure.

 

[bobrayner]

Hippy
Have no idea re the 3.5mm plugs and sockets. Once again it would be a quality issue. The plugs are probably quite robust with the socket contacts being the weak link. The larger (and very expensive) 6.5mm and their "Bantam" counterpart professional units designed to be fitted into jackfields are very good but they are designed for hundreds of mating cycles in a patchfield environment. In fact their worst enemy is a carpeted floor. The fine fibre dust finds its way into the normalising contacts causing no end of intermittent problems.
On the subject of soldering to gold plated connectors. It is NOT a high reliability joint unless the gold plating is removed from the solder bucket. Where the connector has a very thin flash plating a single solder operation is considered adequate to remove the plating. On more heavily plated types the technique is to tin the bucket, remove the solder and repeat the process 3 times. This should get rid of the gold and leave a tinned solder bucket ready to accept a wire. I have seen some Mil Spec connectors where this treatment has already been done.
Cheers BobR

 

[ljg]

I find technicals statement that Rev Ed doesn't rcommend Dconnectors interesting and just a bit puzzling. My admitedly anecdotal experience is that I have never had a D connector fail in any of my processor boards, programmer boards, or experimentors boards from at least 6 manufacturers including Microchip, while I have had breadboard contacts fail from overuse, and I have broken header pins. Since I only have two computers, I constantly plug and unplug cables to robots and boards. A new robot may go through several hundred cycles in the testing phase. I certainly don't see failure after a few cycles.

I had a small hand in the design of one of the most popular robots in the US,(several thousand by now, I venture) and people break them a lot of ways, but I can't recall a single instance where the programming D connector was mentioned as the culprit. I can think of a couple serial cable failures, though at least one of those two was the wire inside the cable that failed.

Anyone else? Is there comparative data to be had? I don't mean manufacturers disclaimers, I mean actual failure rates.

 

[Vadim]

Larry, from my experience all serial link failures were traced to broken wires, sometimes inside connector's enclosure and often due to improper connector installation/handling. A small number of mating cycles guaranted by manufacturers is due to a tight contart resistance requirements - like tens of milliohms. Obviously RS-232 link can tolerate tens of ohms, this is why the number of mating cycles can be some orders of magnitude higher.

 

[ylp88]

An interesting though by Vadim which I did not consider. Especially with a 22K resistor in series with the serial line to the PICAXE serial in pin, even 1K between the contacts would make minimal diference. The 22K resistor could always be reduced, of course.

Wow, what a discussion on something so "simple"... Nice bit of trivia over dinner...

ylp88

 

[BeanieBots]

I am a great fan of D-type connectors and have experienced very few failures except those caused by abuse such cables left in a tool box and the pins getting bent.
On the other hand, I have also been involved with high volume automatic test equipment and they are an absolute NO NO for such applications due to mechanical degredation caused by thousands of insertions of a short period of time. As mentioned by Vadim, they tend to go high resistance and therefore don't meet spec rather than fail completely. In most cases, this would not be problem for the home user.
In the domestic/educational environment, failure is more frequently physical breakage of the cable close to the connector irrespective of connector type.

IMHO, 3.5mm jack type connectors are by far the worst type. It is usually the socket that fails and contact resistance is a function of which way the cable lays but only when there is an R in the month. They also short the signal during insertion/removal. The molex connector (which I prefer) on the other hand is much more fragile physically and would probably not stand up to the rigours of an educational environment. Horses for courses.

 

[Technical]

For clarity, it is worth remembering the primary usage of the PICAXE system, within the educational sector in schools. Less than 5% of PICAXE sales are to the main users of this forum - hobbyists. The desired connector will therefore vary considerably between these two sectors.

Within the educational sector, where students build their own electronic projects to take home, cost is the over-riding factor.

9D sockets are also physically large (making the students project unwieldy), expensive (compared to 3.5mm stereo sockets), and prone to breaking the PCB/solder joints upon insertion (remember on computers etc the 9D connector is often braced by a bracket or casing, not just soldered 'loose' onto a PCB as within a typical school project). They also have a very few rated insertion cycles.

Molex sockets are also cheap, but experience in schools (the very first PICAXE-28 system used these headers) showed the actual cables to be very short-lived in the rough handling environment of a school, the molex style connector/cable joints break after a relatively small time of use.

So it is a compromise on what you are trying to achieve. We would recommend stereo sockets to schools and stereo/molex sockets to hobbyists. We still wouldn't recommend 9D sockets at all, although naturally they would work.

Also as any connector could fail eventually, stereo and molex solders are much easier to replace than 9D sockets.

 

[bobrayner]

Didn't mean to open such a can of worms.
Agree with Vadim. The limitation on number of matings guaranteed is to do with maintaining the specified minimum contact resistance. There are obviously situations where such low resistance is desirable if not mandatory.
I have in fact seen "D" connector failures. In 2 cases they were used in "one off" projects where a lot of developement and fine tuning is done using the saleable item. One case involved a mother board and a couple of daughter boards stacked using "D's", the other used high density "DC62" connectors, panel and cable mounted. The work involved many matings over a period and during the final stages some intermittent problems were pinpointed to connector problems. As both of these uses could be termed "mission critical" and the equipment was to be delivered to site and customer EVERY CONNECTOR (the count would be in the early hundreds) was changed before delivery.
cheers BobR