One DC Power Input Connector Per XO-1 Laptop

   
   
   
   
   

Much has been written here on OLPC News concerning any and all technical aspects of the XO computer. I am Benjamin Nead, an itinerant tinkerer in the broadcasting industry, and I tend to think that just about anybody that takes a critical look at this remarkable machine from afar typically walks away quite impressed with what has been accomplished by the OLPC consortium.

That it has been developed "behind open doors" makes the entire engineering aspect project all the more impressive. Indeed, one can visit the official OLPC web site and study all the details of the XO that one could possibly ask for . . . except, curiously enough, for a rather important one: the size and polarity of the DC power input plug.

olpc xo power connector
OLPC DC power input port

For the record, the official OLPC Hardware Specifications web page has basic electronic criteria, but there's almost nothing in regards to the mechanical aspect of the connector itself

"Power: 2-pin DC -input, 10 to 20 V usable, -50 to 39 V safe, one- time fuse for excessive input"
If one were to visit a typical electronic supply store (which may or may not be conveniently located in one of the various third world countries where the XO will be showing up) and ask for a "2-pin DC -input" connector - or any DC connector, for that matter - the first words from the salesperson behind the counter will be "Which one?", as there is a rather large variety to choose from.

Also, the term "2-pin" doesn't really describe the physically appearance of what OLPC and their collaborators have settled upon. Photos of production XO machines and the most famous matching accessory, the Potenco power generator, indicates that it's a single pin coaxial barrel connector of some sort that (obviously) has two electrical conductors, one negatively (-) charged and the other being positively (+) charged.

Regardless . . . even if you are able to obtain the proper unit, one then also has to determine which wire gets soldered to which pole on the connector. So, being naturally curious, I decided to find out. What harm is there in asking? My initial inquiry with OLPC was greeted with a cheery-toned form letter that referred me right back to very same tech page that I found to be so ambiguously worded.

I then wrote back pointing this out. After several days, no further communication from OLPC seemed to be forthcoming. I next turned my attention towards Potenco and asked the same questions. As with OLPC, they sent me a happily worded generic "thanks for your interest" email that contained no technical information whatsoever.

potenco pull string charger
Potenco 2-pin power connector

I emailed back and politely pressed a little harder for a real answer. The contact person there then cryptically advanced the following:

"I'm afraid that this is something you will need to discuss with OLPC directly. I'm sorry we can't help you more, but it's best that they have this conversation with you. Thanks for understanding."
Well, that's odd. Who wears the pants there anyway and why can't they say which particular $2 Radio Shack part they're using without OLPC's expressed permission? I made mention of this curious correspondence here on OLPC News last week and someone suggested that they (both OLPC and Potenco) might have specified their own specially sized proprietary plug to scare off uninvited third party power supply developers.

I tended to doubt this, though, as it would significantly add to the cost of the machine, where low retail price points are a goal and there is a genuine stated desire to make the computers as field-serviceable as possible. Anyway . . . since I was subtly rebuffed (and I do, after all, have a life beyond enigmatically probing for details on a laptop that I can't even buy yet), I decided to not actively pursue it any further.

That is, until I got another email from OLPC early this past week that stated:

"The latest one I've seen is about 3.25 inches by 2 inches. The voltage and such will be different depending on the country"
Well, I thought to myself, that a pretty damned big plug! And they're going to alter the voltage specifications for different geographic locations? It's obvious that this administrative staff person was confusing a power transformer for a connector, but at least they were kind enough to attempt some basic research and get back to me.

I wrote back (with a visual reference in the form of a hyperlink showing a photo of common connector types) in an attempt to finally get an answer. The reply that I received essentially said they appreciated my interest, but were to busy engineering to answer my question.

Now I was angry. So I fired back with a single sentence email that basically stated that a real engineer would know the difference between a plug and a transformer, signing it with a simple "Goodbye" and expecting that no further contact. But I was surprised, once again, to find a reply to my bitter snipe in my email inbox the next morning, basically restating the same thing that had been said by this same person the day before.

I thought it prudent to write back with a bit more of a controlled response this time. After apologizing for the coarse tone of my previous email, I stated the following in hopes that they would finally appreciate that there just might be a certain amount of importance in having this seemingly obscure statistic available to anyone who bothers to ask :

olpc xo dc power connection
OLPC XO power cord
"The information I'm requesting is NOT presented on any of the OLPC pages. Please believe me when I tell you that I've have combed through all of them very carefully before I began my bothersome email correspondence.

If I (technically adept, too much free time on my hands, etc.) cannot extract this information from the OLPC engineering and public relations oligarchy, then how is someone in one of these third world countries going to get through? What are you going to tell the poor kid in Nigeria who wants to hook up a car battery to his XO when he asks the exact same questions that I have been asking?

This is something that someone in a far more desperate situation than I will be asking of you some day. I would encourage your team to make the power input statistics publicly known at their earliest convenience.

Dual mode screens, state-of-the-art WiFi reception and a cutting edge Linux GUI aside, if you (OLPC) can't tell someone what size power input plug is being used and how it's polarized, then your precious computer becomes a useless plastic brick on an African prairie in no time flat."

As of this past Friday, I have yet to receive a reply. It remains to be seen if I (or anyone who would really needs to know) will be able to extract this information from OLPC.

The XO power plug saga continues.

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26 Comments

I recently received a BTest4 XO for software developing. I'll stick my meter on it when I get a chance and check the polarity.
As for the size, I could prob get the OD of the plug, but the ID might be a little harder for me to gauge.

I'm really surprised, as you are/were, that this information was not on the wiki. I'll post the information I get on the wiki and link it back here. Thanks for getting the ball rolling on this oversight!

I put up a question about this at the wiki.

http://wiki.laptop.org/go/Talk:Battery_and_power#power_input_plug

Thanks Tom and Eduardo . . .

I tried submiting a question on the OLPC wiki myself but I was not successful. It's a much harder system to use than the nice little blog that has been set up for us here.

I tend to think that the metal barrel part of this thing is an off-the-shelf unit. But those close-up photos (above) of the XO input port and power cord that Wayan found for my article now has me thinking that there might be a bit more to the overall design of the plug than just the metal connector. The plastic insulated part looks to be very robust and recessed for weatherproofing purposes. This is probably something that would be very hard to source independently.

I sincerely hope that OLPC will make spare cords - terminated with their special plug at one end, generous in length and with bare wires at the other end (and with polarity indicators) - plentiful and available to any and all who need to hook up their XO computer to an improvised or alternative power source. Wouldn't it be a shame if the only way that you could get one of these connectors would be to trim it off the end of a perfectly good power transformer or Potenco unit?

Sorry to sound like a fanboy, but this exactly the type of thing I turn to this web site for. The informative, inquisitive post by Benjamin, and the quick responses from Tommy and Eduardo -- what a great demonstration of the power of a simple blog to unite expertise and interest around a specific topic.

Nice mix of articles here at OLPCnews of late!

(admins: feel free to not post / delete this post)

As an electronician, I can ensure you that no supply store, be it in third or first world, will provide you with an adaptor where you can choose the power & voltage AND the plug.

Either you find (with much chance) a power supply for a brand (Dell, Sony...)with the appropriate power or you buy a universal power supply with selectable voltage and multiple plugs. That's it.
To move on, what I can say with 99% probability is that the PLPC plug is + outer, - inner, with standard diameter you can find on any universal adapter and power ratings given by OLPC specs.

You're making it a tempest in a teapot and I suspect that OLPC team don't respond satisfactorily because your question is self-evident for a hardware guy and so hard for a software guy.

M,

No need to apologize, I think OLPC News rocks too, exactly because of interactions like this. Now if we can get the actual DC input connector information, we can claim success.

Coaxial power connectors do indeed come in many shapes and form. Almost universally the 'power source' plug has a center female with the 'socket' (on the equipment) using a male pin.

The male pin can be anything from 2.1mm up to 2.7mm and larger. Many a time I've been frustrated trying to use a 'plug pack' power supply with a 2.5mm center hole and the equipment socket using a 2.7mm pin.

Some plug and socket versions also use a shrouded outer cover which provide protection against shorting the normally exposed negative plug terminal. Typically the center is positive (in our 'grounded negative' World).

I dont see the XO laptop power connector as a big mystery, more of just a curiosity.

"I don't see the XO laptop power connector as a big mystery, more of just a curiosity."


Hi Robert . . .

The part itself seems pretty pedestrian. The big mystery is why nobody (thus far) that is "in the know" won't (or can't?) provide a simple set of specifications. We're probably talking about a $2 part that can be purchased at any Radio Shack.

I'll also put my money on a negative
ground on the outer part of the
barrel but I have been "pleasantly surprised" to witness well know electronics manufactures that sell here in the US do it differently just so that a competitor's power supply can't be used with their gear.

I don't have the size specs for you guys, but the polarity was a quick/simple test. The center pole is positive, with the shield being negative.

Center (+), Outside (-)

I'll try to get the size too you soon, just been busy at work. Hope that helps!

Okay, I got my calipers out and the plug is indeed a 2.1mm plug. Sorry for the delay.

I'm sorry to say that I haven't found OLPC itself very forthcoming (understatement of the year?) when I've written to them, either.

I did once get through to a lady on the phone, who told me that "despite their funding etc they were in fact a very small organisation without the time or facilities to interact very much with people outside it."

I took this at face value at the time --- but in fact I now believe the actual case to be that OLPC is too immersed in complicated commercial politics to listen to technical questions from people with soldering irons (or simply with a lively interest in what's going on ) --

-- or (gentle cough . . .) with new ideas . . . ?

It's a great pity, I think, because at bottom they are not only launching one of the greatest and most intelligent humanitarian projects of the past couple of hundred years, but are doing so with a piece of hardware which all of us acknowledge, I think, to be superb and even ground-breaking.

Cheers,

The proper connector might be available at radio shack, but it is not a standard size. I had a "universal" adapter (something like http://www.amazon.com/RCA-Universal-AC-Adapter-AH3WH/dp/B000068IDS ) - one that lets you dial up voltage, and comes with half-a-dozen standard connectors but none of the connectors fit the OLPC.

Just checked the wiki (Aug 23 3:00PM Eastern), and it says this:

External connectors

* DC Power: 6mm (1.65mm center pin) connector; 11 to 18 V input usable, 40 to 40V input tolerated; power draw limited to 15 W;

http://wiki.laptop.org/go/Hardware_specification

Simply marvelous! Spot on comments by all here.

Demensure's remark about being "self-evident for a hardware guy and so hard for a software guy" really hits home with me. I also think that Martin, in particular, has a very keen understanding of the "big picture" of
what's right - and wrong - with OLPC.

But Tommy . . . if you'll pardon the inner city vernacular, "U be dah Man!!" Thanks to you, we now know that the outside diameter is 2.1mm and that it's polarized with negative (-) voltage on the exterior of the barrel. A computer nerd that ALSO has
a set of calipers nearby? You're exactly the guy I've been looking for!

A quick look around the web, though, indicates that 2.1mm diameter connectors are commonly available in 5mm and 5.5mm lengths . . . and
there is no indication if those lengths include the tiny plastic insulating tip or not. I also think that it's valuable to know the basic dimensions of the insulating part of the plug (typically gripped by the fingers when handling) that
disappears within the XO's input jack when plugged in.

So . . . I've assembled a drawing with various mystery dimensions marked off as "A", "B" and so on . . .

http://www.jetex.org/images-ben/XOplugDimenGuess_W.gif

If you have the time and inclination (and your calipers are still close at hand), I think that there would be many here - and certainly a greater number of third world end users that we haven't met yet - who would appreciate you willingness to take a few more measurements. Thanks in advance.

"A" is 3.65mm
"B" is 4.25mm
"C" is 1.85mm (there are 2 "steps" to the boot, but this is the part that touches the XO case.)
"D" is 3.7mm

Uh-oh. I was so tired, I wasn't thinking. Those units aren't metric. They're customary.
So each unit I listed is 1/10th of an inch.
Please adjust accordingly!

A = .365 in
B = .425 in
C = .185 in
D = .370 in

Sorry for the confusion.

Bingo!

I've got to run off to work but I'll have a fully dimensioned scale drawing completed and linked here tomorrow.

Thanks again, Tommy.

Well . . . here I am at work with a bit of quiet time on my hands. Thinking about Tommy's gaff in mixing up metric figures with machinist scale inches reminds me of when Lockheed Martin did the same thing with navigation coordinates for a Mars probe back in 1999. The thing went 3,500 miles off course and was lost forever. Millions of Dollars down the drain and a lot of red faces that day. Good to know we're not in that boat.

I've also had time tonight to run Tommy's decimal inch figures into an online inches-to-metric converter and came up with a pretty interesting set of statistics.

Now that we know that we are dealing with a 0.21" outside diameter barrel (give or take a few thousands of an inch), that translates to 5.334mm. Likewise, total length of the pin including the plastic insulator tip (I referred to it as "A" earlier today on my drawing) comes out to 0.365" and a direct metric translation would be 9.271mm.

Next . . . a trip around the web with the Google search engine indicates that everybody and his brother sells barrel connectors in metric dimensions, never measured inches.

A 5.3mm X 9.3mm barrel connector is something that is not to be found. But 5.5mm X 9.5mm sizes
(with either a 2.1mm or 2.5mm internal barrel diameter) are extremely common.
Take a look . . .

http://www.powerstream.com/C.htm

I'm going to bet that OLPC is buying common sized connectors by the millions rather than specifying an oddball sized item that would cost them a lot of money to have made and cause additional compatibility headaches down the road.

Now that we are (almost) certain that this is a garden variety 5.5mm X 9.5mm item, we might as well peg it and get the internal diameter to boot.

Tommy . . . could you take the power transformer (or the XO) down to a local electronics store
and ask the friendly person behind the counter to see if this is a 2.1mm or 2.5mm internal diameter pin?

Alternately (if you don't want to be walking around town with all that stuff) stop by a hardware store and pick up a #49 machinist drill bit (exactly 2.4892mm / 0.098" in diameter . . . and about 75 Cents, the last time that I checked)and insert it into the interior of the barrel. If it fits, we're dealing with the 2.5mm variety. Mystery solved . . . and you've got a very nice drill bit left over when your done.

After this, I'll let you get back to your programming work, Tommy. Thanks again for allowing me to drive you to the same level of craziness that I occupy on a daily basis! :-)

Ben,

It looks like your efforts have paid off. Walter Bender updated the OLPC Wiki at midnight on the 22nd with the specifications that "kslays" notes above: http://wiki.laptop.org/index.php?title=Hardware_specification&diff=61245&oldid=61047

Hi all . . .

Very interesting. As soon as I saw the new OLPC DC connector specifications this morning, I jotted them down and headed off to the local electronic parts supply store. After a very quick math equation (which, in actuality, I did before leaving the house) I've determined that the XO (within a 99% probability) is using a 5.5mm OD X 2.1mm ID X 9.5mm L plug . . . a very common item in the world of consumer electronics.

Some thoughts . . .

I was initially thrown off by OLPC's new "6mm / 1.65mm pin" specification but then I realized this was for the female jack that would be mounted on the motherboard, not the male connector itself. If we are, indeed, dealing with a 5.5mm diameter male plug, then this
is a tolerance of just 0.5mm. Likewise, a 1.65mm pin on the female part is only 0.45mm smaller than the interior diameter of a 2.1mm male plug's inner sleeve. This clue allowed me to eliminate the
2.5mm inner sleeve on the male connector from the running. No need to purchase that #40 machinist drill bit, Tommy!

I recounted a brief version of the (now very long) story to the electronic store cleck . . . not a young kid but, in fact, a fellow who has been selling these sort of parts since vacuum tubes were considered modern technology. He confirmed my detective/math work and noted that the sub-millimeter tolerances between the male and female parts sounded right to him (both the 6mm sleeve on the female part and the 2.1mm sleeve
on the male plug would be "Coke bottle" shaped inside
to help grip the opposite surfaces on the corresponding parts.

He found the "6mm / 1.65mm pin" spec for the female jack, while certainly more revealing than "two pin connector", to be atypically of a description usually found in the industry. "Kind of like measuring the diameter water flowing through a pipe instead of measuring the pipe itself" is how he summed it up. I have to agree.

There will be, for certain, a far greater number of people purchasing male plugs to connect batteries and solar panels onto their XOs than those wanting to swap out the corresponding female part inside the computer itself. Why not reword the specification to assist in this endeavor? This most recent XO specification revision also doesn't indicate the length of the male connector nor does it give a clue to polarity. Beyond any of this, I'm also confused as to what they mean by "40 to 40V tolerated." This is, I'm guessing, a misprint for "4 to 40V tolerated."

Anyway . . . OLPC could do much worse than to hyperlink to a drawing such as this off of their official specifications web page . . .

http://www.jetex.org/images-ben/XO_DCplug_Specifications_W.gif

I'll send it along in an email to them and see what they have to say. Thanks again to all here on OLPC News who assisted here over these past few days.

So let me get this straight. You get mad for e-mailing a general address with a technical question when there are other, almost real time places to ask said question and get an answer of that nature? What our nice receptionist said is true, OLPC is a small organization with most of us working to actually produce the machine. She is nice enough herself to stay late and respond to every single one of the e-mails that come through, even if it is with a copy and paste response. She even passes questions back to others, which was your experience though through the "telephone" effect the question may have gotten distorted.

But that is all besides the point that you could have easily filed a bug at http://dev.laptop.org since you are correct this was an oversight. Or you could have e-mailed the technical mailing list or signed onto irc at freenode.net (#olpc or #sugar for software questions). Note that we are still human and not all inquiries will be able to be answered right away as we need to prioritize our time.

Hello John "J5" . . .

How do I begin to respond to this in a constructive manner? First, by saying that the "official" forms of contact (the wiki and this other site that you have just mentioned, which I've never seen before) are woefully inadequate two-way communication devices.

Having poked around the wiki for the better part of an hour one day and finding it impossible to bring up a typing form or an email link, I simply gave up. I'm also unable to find a similar easy-to-use interface on this other site. Please excuse my human fallibility (and I'll excuse yours) in not being to successfully interact with the system that is now in place to address OLPC engineering concerns.

Logic dicatates, though, that most outsiders will approach OLPC through the main web site (as I eventually did) and hunt for an appropiate email link from there. With a very large number of machines that are going to be showing up in the field very soon, I would expect this to be a more commonplace experience for your staff and I would hope that OLPC is preparing for it.

Thank you acknowledging oversite and all, needless to say, is forgiven. My intention was not to "rock the boat" simply for the sake of doing so. But I, like so many others, don't respond favorably to passive avoidance when my initial inquiries (I think) were clear and succinct.

We both know the importance of the DC power input on any sort of device like this. Now, one can hope that the next time someone asks 'what size power connector and how is it wired?' someone at the other end can say '5.5mm OD X 2.1mm ID X 9.5mm L, negative DC on the external barrel' in fairly short
order. If my little exersize has made it easier for the next person to ask the same question - and easier for your receptionist to field it - without the same frustration that all of us just endured these past few weeks, it will have been worth it.

John Palmieri wrote
"Note that we are still human and not all inquiries will be able to be answered right away as we need to prioritize our time."

Thats the crux of the problem, John. Priorities are involved. You guys are all trying to push out a hardware and software package (and associated items) with a small team of paid staff and a huge group of volunteers.

When it comes down to it, the size of a power plug just does not figure into the equation. XO's come with a plug pack power supply (or the Potenco pull cord device some time in the future) so why would the specs for a power connector matter?

On the other side of the coin, the OLPC initiative has generated World Wide interest - maybe more than the current 'Media Lab' environment was designed for. The hardware is amazing, the software is innovative - no wonder we all want one.

So don't be dismayed when someone like Benjamin discovers that there is a big gap between the 'Hype' on the Laptop.org site, the mess that is the Wiki and the organised chaos that is the Dev (Trac) site.

I also note that the Dev.laptop.org main page clearly states:
"Our general project wiki is at http://wiki.laptop.org -- the site you're currently browsing is ONLY for bug tracking, and source code."

Obviously not a place to ask about the size of a power connector.

Hi Robert . . .

It's personally reassuring to know that I'm not the only one who has found the OLPC wiki to be "organized chaos" but I feel empathy for anyone has no other course of action than to interact with it. I don't have an easy answer on how it can be improved other than to modify the interface so that a typing form is literally staring you in the face as soon as the page opens, much as you are able to find on this site.

I also want to reiterate, if I haven't made it clear already, that I think that the OLPC mission is a noble one and that my personal mission to extract power plug information from them was not an attempt to embarrase, belittle or to harass. If I've exposed flaws in the communication system then I hope that something can be learned from it to make it better . . . and not just sit back and sardonically shake my finger at it.

But, not wishing to beat a dead horse into the ground, I'll take issue with your observation to John . . .

"XO's come with a plug pack power supply (or the Potenco pull cord device some time in the future) so why would the specs for a power connector matter?"

It matters because in real world conditions that I've envisioned (and probably several hundred others that I haven't thought of yet) the DC transformer and/or the Potenco might break, get lost or stolen. If another power source has to be substituted then success comes down to knowing the precise measurements of
a rather pedestrian part . . . one that has virtually dozens of other substitutes that look identical to it to the untrained eye but simply won't work because they
differ in dimension by a millimeter (or less) on one axis or another.

USB plugs (for data transfer and periphials) and 3.5mm stereo connectors (for audio I/O) are the only other connectors that one has to concern oneself with on the XO. But there aren't dozens of similarly sized USB connectors or earphone jacks to worry about . . . and none of the items that plug into the XO on those connectors do anything as important as charge the internal battery or, indeed, keep the machine turned on and functioning.

It's frustrating enough for me when I have to hop back into my air conditioned car for a 10 minute drive across town back to the part supply house to get the correct widget for whatever I'm working on when I picked up the wrong one on the first trip. Imagine how much more complex and labor intensive the same task is going to be for a third world XO owner when
the journey to the part supplier is considerably longer, more expensive, and dangerous.

http://wiki.laptop.org/go/Battery_and_power

The XO DC jack specs:
1.67mm Center pin diameter
5.5mm Outer barrel diameter
11mm contact length

Mechanical Drawing Image:DCJack.pdf

Some off-the-shelf parts that work:

(courtesy Richard Smith and Arjun Sarwal)
Digikey part #CP-2199-ND (right angle) Current recommended part, tested at the OLPC office in Boston
Digikey part #CP-2195-ND

The charger for my IBM Thinkpad T42 laptop works in my OLPC. Hopefully you can find the specs for that online, or find retailers that have connectors/adapters for the more common Thinkpad.

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