some rough cost estimates

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some rough cost estimates

Werner Almesberger
Some cost estimates for the components: first of all, the cost
consists of two parts, the actual cost of the component, and what
goes into shipping and handling. The latter depends mainly on the
number of sources, not so much on the number of components.

Component prices vary with quantity. If you buy, say, a single 10
kOhm resistor in a 0402 package from Digi-Key, it will cost you
about 2 dollar-cents. Buy a reel with 10'000 such resistors on
it and the price drops to 0.132 cents apiece. Buy many reels and
it still gets cheaper.

We're unfortunately in quantities where such discounts help very
little. So given a price for large volumes, the same item will
probably cost us 2-5 times that amount. For a rough estimate,
let's assume a factor of three.

Another problem are parts that have large minimum order quantities.
Manufacturers like to sell boxes full of reels. Many will let you
buy entire reels, but it doesn't get smaller than this. Of course,
an entire reel of anything would almost always be way too much for
our purposes.

For these cases, there are two possibilities: 1) find a distributor
like Digi-Key, Mouser, Arrow, Farnell, etc., who buys entire reels
and then sell small fractions of them. They charge of course for
this service, see the example above. Also, they only do this for
components where they can reasonably expect to eventually sell most
of the reel. 2) ask the manufacturer for samples. This is less
structured than just buying from a shop. A manufacturer will have
some requirements for anyone to qualify as a suitable recipient of
samples, and the amount of rigmarole for convincing them that you
do can vary greatly.

Okay, now to the cost estimate. What I have is a happy mixture of
prices for "typical" volumes, typically large, and without
suppliers. Based on this, the items in
would have a value of about USD 1100. Applying the factor of three,
we'd be at USD 3300.

Big-ticket items are the CPU, the WLAN module, and the Bluetooth
module. They also happen to be things you don't find so easily on
the market. We may try to get samples, which would unburden our
budget considerably.

If we assume that shipping and handling, payment overhead, etc.,
per source costs about USD 200, and if we further assume that we
have to order from five different sources, this would add another

Next, we have the parts we already found at Digi-Key. For them, we
have an exact price: USD 536.65 (make optimist show-dk), plus

Next, we have a few stray parts in bom/dummy.inv, namely the GSM
module, acceleration sensors, speaker, and vibrator. All together,
they're probably around USD 100 per device (the GSM module being
the pricy bit), USD 2000 in total.

Then there's the LCM module. Prices seem to vary widely, but let's
assume it's possbile to get 20 units for about USD 1000, including

This leaves the parts which are missing in FIC's inventory and for
which we have't found substitutes yet (make show-missing). Looking
at the expensive ones and just guessing small things like resistors
and capacitors, the cost adjusted for low quantity should be around
USD 1000. Again assuming five different sources would add another
USD 1000.

Not included: pretty much anything that doesn't go on the PCB, such
as various antennas, speaker, vibrator. Shields. Case. Battery.

Let's to the total now:

ee-bom-fic-20100208 3300
  overhead 1000
digi-key (incl. overhead)  750
dummy (incl. overhead) 2000
LCM (incl. overhead) 1000
missing 1000
  overhead 1000

That's for 20 devices, minus any screw-ups that happen in design or
SMT. Assuming a somewhat optimistic overall yield of 75%, that would
be USD 666 per device. Heh, nice numbers, and I didn't even have to
go back and "tune" them ;-)

While it's a lot of money, this still looks doable, particularly if
we can bolster our budget with donations and lower the cost through

- Werner

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