(For all images, click on the thumbnail for a larger picture.)
The first problem when attaching sensors to the Tmote Sky is making
the physical connection to the board. Apparently the designers made a
peculiar decision which makes this task a bit more complicated than
one might expect.
As the mechanical drawing shows, there are two IDC headers that give
access to the sensor channels: one 10 pin (tag 4) and one 6 pin (tag
5). The physical layout does not maintain 0.1 inch spacing between
the two headers, though, so it's not possible to bridge both of them
with one 16 pin connector.
However, they're not far enough apart to allow two typical connectors,
Here, I've connected a 10 pin ribbon cable, with an ordinary crimp-on
connector, to the Tmote's 10 pin header ... but it pushes right up
against the 6 pin header and doesn't allow access to it. I haven't
been able to find any other crimp-on ribbon cable connector that's
narrower than this.
The solution is to use small profile headers that can fit right up
next to each other. I chose to mount two such headers on a single 16
strand ribbon cable, but you could put the headers on separate cables
if you prefer. Here are the part numbers for the headers I chose:
|Part ||Molex part number ||Digikey part number ||Quantity |
|10 position housing ||22-55-2101 ||WM2522-ND ||1|
|6 position housing ||22-55-2061 ||WM2520-ND ||1|
|crimp terminals ||16-02-0103 ||WM2512-ND ||16|
It is tedious but straightforward to crimp the 16 individual terminals
onto the ribbon cable's 16 conductors.
Once the terminals have been threaded into the housings, the result is
a nice neat connection to the breadboard. Of course, the pinout at
the other end depends on where you put which terminal. Here's my
pinout, with the connectors physically arranged to reflect the layout
of the DIP plug at the other end of the ribbon cable.
Why this is of only transient importance
This cabling issue only matters for breadboarding ... once our design
is solid enough for PCB fabrication, we can put the header pins on our
PCB anywhere we want. (In fact, someone at Moteiv said that this is
exactly why they can't change this odd layout -- other customers have
already built their boards to interface with this existing layout, so
Moteiv has to stay compatible with its customer base.) But
breadboarding is a useful phase of design, and it's nice to be able to
prototype and test the circuit before committing to PCB fabrication.
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Last updated 30 December 2005