The long-languishing linear LED lighter is back in my “get it done” pool. I have the parts sourced, the design refined, and a big bag of utterly failed attempts to print an acceptable case for it on my CupCake. Fine. Forget the case. No case.
The project, to refresh your memory, is a linear driver for three strings of LEDs, up to 40V and 100mA per string. You supply your own power (5-40VDC), LEDs, and wire.
After spending two hours looking through 250 pages of connectors in the Digi-Key online catalog (I am not kidding), I’m distressed to discover that the least expensive connectors I can find are going to cost about $2 per board. Feh! But I want the power and LED connectors to be polarized, and that’s more expensive than plain ol’ .1″ headers.
Here’s a mockup (clickable for the big pic, like all the photos here) of an early prototype PCB with product photos of the connectors I’m leaning toward. On the right, a six-pin header for three LED strings and a representative two-pin plug that’s polarized by virtue of the semi-latching bump. On the left, a two-pin header for power and definitely-latching matching plug.
Note that the male connectors are on the board to reduce the opportunity for shorting what’s on the ends of the wires while they’re unplugged and flailing around.
Questions:
- Is it reasonable to expect people to plug three two-pin connectors into the right places in a six-pin header?
- Is it worth making the power connector different from the LED connectors, to make it harder to misconnect things?
- How many people are going to crimp pins onto the wrong wires and have to start over?
Opinions in the comments, please.
If you think you can find me less-expensive polarized connectors with .1″ spacing (I want to offer the driver with straight male headers for breadboard friendliness) that I can buy from a supplier as reputable as Digi-Key, please provide direct links to at least the header and ideally the plug and crimp pins. Free LED driver if you actually come up with something I like better.
Addenda 21-Mar-2010
Thanks for the responses so far! A few additional notes:
Connector Cost
The connectors I show above come to about $2 total per board, not $2 each. That’s still a larger fraction of the electronics cost than I’m happy about.
Connector Size and PCB Size
The current iteration of the board layout is much smaller than that shown above:
I’m trying to make it as small as possible (A) on principle, (B) to save on board manufacturing cost, and (C) to make it easy to “hide” the driver within whatever you’re building. I have a little more optimization to do; but you can see that the board size will very soon be determined by the size of the connectors.
Because of this, I would really rather not leave extra “key” pins in the LED string connector — they’d widen the board. (Arguably I could then shorten it, but I’m not convinced I could really make that happen, given the distance I need to fan traces out from the TSSOP. The TQFN pinout doesn’t make things significantly better, either.) I’d also rather not use connectors with “walls” between the two-pin pieces, as they’d increase the PCB width (height?) by at least .2″.
Also if I go with the six-pin connector idea, the female headers need to have thin outer walls so they can fit side-by-side between adjacent pins.
LEDs and 6-Pin Connector
By my read of the MAX16823 datasheet, if you misplug an LED string one pin off, it simply won’t light, nondestructive to both the LED and the string. I assume you would then look at the plug and see you had misplugged it and replug it correctly — so this should not be a catastrophic event.
I also intend to indicate the correct divisions of the 6-pin connector in silkscreen.
I know people will still get it wrong occasionally, but since it won’t hurt anything — good enough?
Addendum Noon 21-Mar-2010
Asmodeus has found the connectors I want to use and pointed out the (obvious) way to space them to meet my board criteria.
If I need further input, I’ll mock up another picture with the latest plan and start a new post. Thanks to you all, and comments are now closed!
You didn’t mention what wire gauge you want but these are one of my favorite connectors since its pretty easy to get a good crimp, the tool is cheap and you can use a small screwdriver if you are desperate. The ones you need run $1.12 for quantity 1, and more are obviously cheaper.
6 Pin Receptacle
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A31021-ND
$0.32
6 Pin Header
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19454-ND
$0.31
2 Pin Receptacle
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A31017-ND
$0.19
2 Pin Header
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19450-ND
$0.30
The MTA100 tool
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A9982-ND
$19.20
Assembly Video
http://www.youtube.com/watch?v=wcLvW1XhDJY
Just assume that the people buying these are complete idiots. They probably won’t be, but it’s best to assume anyways because you never know for sure. That should answer all of the questions.
1. No.
2. Yes.
3. Lots.
I use JS-1001-02. It is not easy to find but you can get them for very cheep out of China.
Answer to questions:
1, You’d think it would be reasonable, especially for makers, but people will always surprise. The polarised connectors will mean they cant plug them in back-to-front in the right place, but they can still miss by 1 pin, which would end up being backward. Possible solution is to put a blank pin between the outputs, giving 8 pins total (ie, +-B+-B+-) this means even if they miss by 1 pin, then it just goes nowhere instead of backward. Another option would be to give a 6pin plug instead of 3x 2pin.
2, Yes, definitely worth it, don’t want power going into outputs.
3, From what I can see in your pictures, the process is crimp onto wire, push crimp into holder. If you put them in the wrong way, you can take them out again (with a small screwdriver to push down the retaining pin) and do it properly, without having to re-crimp. So this shouldn’t be an issue. There are also plugable terminal blocks, but these are probably too bulky for your needs, smallest pitch seems to be 3.5mm.
My question to you:
$2 per board isn’t a huge amount, but $2 per connector is boutique electronics store prices, and you can get better prices off proper distributors. eg http://au.farnell.com/tyco-electronics-amp/640454-6/pin-header/dp/588519 which is a part that looks pretty much the same as your right side connector (albeit not right-angle, but I believe they are available in right-angle too). That distributor is global, so I assume their prices would be similar world-wide and that connector is only AU$0.52, which would be slightly less then $0.50 US. And it drops considerably if ordered in quantity, virtually half price at 25-49
Is that $2 pricetag per connector per board, or for all the connectors for the board? I wasn’t able to find the connectors you mentioned on digikey to check this (probably because I haven’t spent 2 hours looking
Just do the ole standby and leave a gap-tooth space in the male header and jam a pin in the corresponding female part like they used to do on some old PC connectors. It’s dirt cheap and works well enough. Heck, you could even snip off one of the mail headers after soldering it and use that to plug the corresponding hole.
Did you look at Jameco? I found some latching connecters under .50 each. If I remember in the morning I’ll try to find the numbers for you – I was on a similar journey.
I can think of a few things:
IDC connectors like the MakerBot’s motherboard to motor driver rainbow cables.
Look at how a lot of fluorescent ballasts do it:
Some use screw terminals and just print stickers to label the terminals. Some even come with the ability for the screw part to unplug from a male header on the board.
Similar to the screw terminals, is a terminal that is spring loaded and has to be pushed down in order to insert a wire.
Wires soldered directly to the board. The installer (customer) has to connect each wire to the appropriate wire with wire nuts.
Other than that, you could use connectors with twice as many pins as are needed and only use the odd (or even) numbered pins, leaving the remainder unconnected on the board (not even grounded). This would allow a non-destructive reversed connection.
Maybe you could make some parametric open-source 3-D printable connectors?
Hope this helps. Good luck!
Asking people to put 3x 2-pin plugs in a 6-pin one might defeat the purpose of polarized: if you put them in wrong, you will connect things in reverse anyway.
Another way to prevent reversed connections is to connect only 2 pins of a 3-pin header. Then you could use simple unpolarized 0.1″ headers.
Cost savings, my favourite topic!
Well, Sparkfun also has very cheap polarized 6-pin headers – just search for “ICSP” on their site. 8 cents/piece for 100+.
Anyway, a cheaper option: Use 3-pin polarized connectors for input power, and three separate 2-pin polarized connectors for output.
Input: A99614-ND housing (.0868), A19451-ND header (.0869), 2x crimp pins (.0222/piece), for a sum of 22 cents.
Output: A99613-ND housing (.0412), A19450-ND header (.0631), 2x crimp pins (same as above, .0222/piece), for a sum of 15 cents/piece, and since you need three, 45 cents total.
So per box you end up at 67 cents for connectors, and you can’t mistake input and output connectors either. Not too shoddy. Note, I’m using pricing for 100+ connectors, but you can get all of these in single-unit quantities too (for not much more).
Good luck!
Links (didn’t want to stick them in the other comment due to the spamishness):
Crimp pins: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A100453CT-ND
2-pin header: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19450-ND
2-pin housing: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A99613-ND
3-pin header: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A19451-ND
3-pin housing: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A99614-ND
Cham and others — I was already intending to provide at least one extra crimp pin per connector. Since the pins are relatively inexpensive compared to the rest, I could provide two or three each.
Devlin — I like IDC ribbon cables, but I don’t recall seeing them for only two pins. I want the three LED strings to be independently pluggable, not attached together into a three-string block out of necessity.
Asmodeus — you found exactly the connector I had in mind when I searched Digi-Key, and I didn’t run across them. You now have the connectors to beat! (And a driver or two owed to you once they’re assembled, if you’re interested.) Thank you!
Drat. Asmodeus, the female housings have sidewalls thick enough that these won’t fit side-by-side on adjacent male pins. I’d have to leave a space between two-pin LED connectors — and to keep this possible to plug into a breadboard using different connectors, it’d have to be a .1″ space.
I’m staring at the datasheet and I just can’t get around that.
I’ll look at widening the PCB — it may be worth it in order to use these connectors.
Hm. But you don’t have to widen it a whole lot; a single millimeter is enough, if you want to keep the same hole-to-board-edge spacing.
Did a quick mockup of the difference: http://dump.gpio.org/headerwidth1.png
So if you instead use a pinout like this, which will allow both .100″ spacing for breadboarding as well as these connectors:
http://dump.gpio.org/fixedspacing.png
Ough to work, and doesn’t really take much more space.
If you do end up using them: Sure, I’d love one. I’ve got some 3s16p LED arrays which should be right on target, and I was planning on building a driver for them at some point in the future (http://www.dealextreme.com/details.dx/sku.13190).
A few thoughts:
1) For input, you could consider putting a FW bridge on the input so that you can plug it in either way. Extra cost though. Or, you could make it a three-pin connector, with ground in the middle and Vcc connected on the board to either side. That gives you an unpolarized connector – as long as they get the pins aligned, it wors.
2) For the LEDs, you could consider doing the same thing, though that would require more board space. I think it’s okay if the LEDs just don’t work if you hook them up backwards. You could also consider a 2x connector.
Futurlec sells the connectors/pins/etc that you want. I’ll vouch for Futurlec, I’ve ordered 3 orders from them, each over $150 and they’ve all arrived in about 2 weeks with their standard shipping, you can pay more and get them faster.
http://futurlec.com/ConnPolHead.shtml
Only issue I ever had was they delayed shipping my order by 5 days to get 1 part in stock, I followed up and told them to ship without the part and they had it out that day.
Asmodeus, thanks for pointing out the obvious technique of separate holes for the breadboard and off-board connections! That’ll work marvelously and the Tyco connectors you found are perfect.