Small, easy to find, cheap alternate jtag/isp plug ?

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#1
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I'm making a tiny board (1.5 inches), using only small packages and SMT.
The thing is, the minimum of 6 header pins for ISP is starting to look 'big' compared to the rest..

So, do you guys use alternative connectors ? I'd like to find something that is a lot smaller than normal 2.54 pin headers, but is also readily available...

I considered using a USB-B '2' connector, because it has 5 internal pins + case.. that should work for ISP.. However the connector turns out to have a fairly large footprint anyway, because of the 'user proof' casing...

Author of simavr - Follow me on twitter : @buserror

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molex connectors? small SMD ribbon cable connectors... There are a lot of alternatives ;)

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Well yeah I know there are lots of alternatives, thats why I ask for recommendations :D
I'm not going to iterate thru all the combinations :D

Author of simavr - Follow me on twitter : @buserror

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I had the same problem for a 10 pin JTAG connector, a normal 0.1" looks so big indeed ;) So I used a 1.27mm 10 pin socket, which looks much sweeter :)

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If you had a bootloader in the chip, it would solve the size. But, than there's the chicken and the egg problem :-(

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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The jtag site on the pc board just needs 10 holes.... lets say you use a microscopic 1mm spacing double row header from samtec.... you just need to build a 1mm 10 pin adapter to the regular jtag connector.

Imagecraft compiler user

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Or why use connectors at all? just make a few 'test points' on the board and use those spring loaded pins. Dunno what they are called.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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I saw a similarly small board that used a 6-pin Hirose connector. Not sure they saved much space, but it was physically smaller than the 6-pin 0.100" spacing header that's typically used. I think the spring loaded pin idea would be even smaller, though.

Tom

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Oh, use pogo pins. The board would have no connector part - instaead it would just have an exposed gold plated (preferably) pad. The rest is simple. Google for pogo pin.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.

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I finaly settled on a 14 way ribbon with 0.5mm pitch. The connector is very small, and I defined myself a pin assignment that allows for :
+ 5V (from USB)
+ 3.3V regulated
+ ISP
+ JTAG
+ One LED
+ TX/RX from the UART

I aldo made a small adapter board for the generic molex connectors for ISP 10/6 and JTAG 10.

So if all goes well I just have to add that connector to all of my boards, and I can bring them up, and debug them in no time :D I don't even need a reset button, I added that to the adapter board.

Here's the adapter board:

And the 'target' device I added to a project. Here just ISP/UART and 5V

Author of simavr - Follow me on twitter : @buserror

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Looking Good Michael!
Cheers,
John

Resistance is futile…… You will be compiled!

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I never posted the resulting board photo, so since someone else was mentioning a similar need on another topic, here it is.

Author of simavr - Follow me on twitter : @buserror

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Nice board! The blue solder mask with gold is quite stunning. Any plan to make these boards available for sale? Now that you've used one, what have you learned and what changes would you make on the next version? Have you run into any problems using the JTAGICE mkII for debugging because of the added effective cable length?

Tom

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Thanks ! Well I don't really plan to sell any, I made just 5 thinking it'd be enough for quite some time :-)

Yes I populated two so far. Not in the picture is also a tiny board with just the 'target' connector and 2.54 headers, so I can put that onto a breadboard and quickly get power, reset, a led and ISP/JTAG on a 'naked' AVR. Thats very tinker friendly :D

I originaly used the 14 way flat cable from farnell, that is 20cm+ (no choice of size) and that didn't work, so instead I cut it to about 8cm or so and 'redid' the end (cut the plastic on about 1cm and added a piece of electrical tape as 'support') and it not only fit very well, it also allowed the MkII to work as expected. The MkII is indeed quite sensitive to extra capacitance, thats moderately annoying :/

One thing that I would change in a further version is to possibly use a line back from the target board with the 'vref' voltage (ie the voltage the target runs at) and route that to the 'vcc' pin of the JTAG header. As I now understand it, the 'vcc' pin of JTAG is in fact, a vref... I didn't know that at the time I made it ! I supose it would be important only for "generic" JTAG for FPGAs etc...

Oh, the gold/blue board is indeed absolutely gorgeous, however there is a catch: if you use solder paste without a stencil, you have to make sure to cover the pads completely, or tin the pads (I use a used piece of wick!) before reflowing -- otherwise the paste doesn't magicaly flow on the whole surface.
So I think my next board will have normal tin pads, unless I find a cheap way to get stencils.

Otherwise, for one of my very first electronic board (part of my second batch, ever!), it's quite a success :D

Author of simavr - Follow me on twitter : @buserror

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It ain't no gold! :mrgreen:

It's just plain copper covered with an organic protective coating ;)

It would be quite a shame and waste to put such expensive material on it, only to cover it later on with solder :)

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Hi buserror,
Try http://smtstencil.com/ for fairly inexpensive stencils.
Regards
Dez Ellis