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Topic: Interfacing the XPort Direct (Read 2011 times) previous topic - next topic

TDG

Bit of an off-topic question this one, but can't think of anywhere better to ask it

I'm trying to interface my Xport Direct with my Decimeilla... I don't want to use the Ladyada ethernet shield (it's good, but I don't need it's functionality and size), I already have capacitors/vregs etc. to get a clean 3.3v, I just need to connect the Xport

Problem is of course, the weird 2mm pin pitch the Xport seems to have. I'm still new to electronic so I don't know how to interface with it?! Is there any simple way without having to fab your own custom PCB?

Like... is there somewhere (I'm in the UK here so it needs to be UK) where you can buy 2mm (0.079") -> 2.54mm (0.1") connects, ie a female 2mm socket on one side and male 2.54mm on the other? What's the simplest way to connect to this crazy pin layout?!

Thanks guys!

BigMike

For prototyping, you can use a small length of ribbon cable.

Note that the XPort needs some additional heatsinking - a bulldog clip is probably enough :)

Regards,

Mike

cairn

It's well hidden on their website (it's under "Surface Mount Proto Boards for some reason), but NKC Electronics sells a simple breakout board for the XPort Direct.

TDG

Thanks for the replies guys

Cairn: Thanks, I've gone ahead and bought that! Looks good. The international delivery adds a bit to the price but it's reasonable unlike most stores, hopefully I'll get a bit of sucess with that

BigMike: Thanks too. Not sure what you meant about the additional heatsinking though? Does it get extremely hot?

madworm

#4
Sep 29, 2008, 08:49 pm Last Edit: Sep 29, 2008, 08:52 pm by madworm Reason: 1
I got one of those shields from adafruit and put the xport+ on it. This one really gets hot to the touch, painfully hot. As I didn't have a heat sink at hand, I changed it's clock speed to low. Helped a bit, but I don't  know if that is also possible with it's smaller brother.
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TDG

Interesting! I never would've suspected it'd get extremely hot like that given that I assumed it was a fairly simple device with not much power involved

Good to know though, better to find these things out beforehand!

BigMike

The spec for the XPort says that it needs areas of copper on the PCB to help with heat-sinking.  The first release of the ADAFruit shield did not have this.

One of these should help:



Regards,

Mike


TDG

Sorry for being stupid, but how exactly would I attach the clip to the xport direct? It's tiny and all plastic on top... and the shield would be on the bottom...?

Couldn't find the bit in the docs about the heat-sinking, I'm probably looking in the wrong place

TDG

Sorry for being stupid again... but does anyone have a wiring diagram or something for the xport direct (like the ladyada ethernet shield would connect it)

I can't quite figure it out from the pictures because there isn't pictures of both sides of the shield... and I'm still a complete electronics newbie so I can't figure it out myself

I've got my 3.3v linreg, 2 x 0.1uF ceramic capacitor and 2x 100uF electrolytic capacitors ready to go to get a stable 3.3V from the arduino

TDG

Got it working after a little bit of playing... seems to work great. I only used two capacitors and a linreg to get a clean 3.3v instead of the 4 capacitors on the ladyada shield... I hope that's ok!

My xport doesn't seem to heat up at all... even after it's been on and working away for several hours, strange

Now just to get the thing doing something useful! It seems a little flaky sometimes...

BigMike

Sorry about the clip - I thought you were using one of these:



If your device doesn't get warm, it doesn't need any extra heat sinking.

Well done for getting it going.

Regards,

Mike



TDG

OK... so I wired it up roughly like so (sorry, I'm not very good with Eagle):



I've only used one set of capacitors for the input voltage to the xport (3.3v linreg), I know the ladyada shield uses two... thing is, the xport seems to work perfectly like this. The various serial ports on the xport are directly connected to various digital output pins on the arduino

Is there a problem with the fact I'm missing the second set of capacitors? Where would these normally go?

And one other question... why do the xport examples posted seem to do a complete reset of the xport every time (in the loop) they want to make a new connection, is a full reset really necessary? The wait for it to renegotiate the link is quite annoying

TDG


t11s

And one other question... why do the xport examples posted seem to do a complete reset of the xport every time (in the loop) they want to make a new connection, is a full reset really necessary? The wait for it to renegotiate the link is quite annoying

You read my mind!  I've had a hard time getting the Xport Direct to actually disconnect a TCP session initiated with AF_Xport or event through the "normal" Xport mechanisms with AF_Softserial, like the "modem mode".   No luck disconnecting and reconnecting after the first connect without using the reset!

Grumpy_Mike

Quote
I'm missing the second set of capacitors? Where would these normally go?


There would be a extra capacitor across each of the two already there. A 0.1uF across C1 and something like a 25uF across C2.
This is because capacitors have a "self resonant" value where the inductance in capacitor balances out the capacitance. So at frequencies above this self resonance they stop acting like capacitors and start looking like inductors, therefore they are not doing the decoupling job they are meant to do. This would result in flaky or erratic operation especially in the presence of noise.

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