From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-05-26 13:30:30
--- In buildcheapeeg_at_yahoogroups.com, "yaniv_vi" <yaniv_vi_at_yahoo.com> wrote:
> hi
> cool . the numbers sound great . it sound that at the moment we can
> offer a real low cost machine ( at least for anybody who can
build) ,
> and that's pretty much.
> a few questions :
> 1. the price s you quoted for parts are for what qty? what are
prices
> for larger qty's like 10 , 50 and 100 ?
Hi Yaniv,
The quote is for single quantities. I must confess I miscalculated
some. Since Digikey does not let you order less then a certain number
of each part type, you will be getting $10 worth of parts you don't
need if you order from them, so the real parts cost is about $70...
sorry about that.
Anyway, ordering for 10 units saves $20 per unit (in parts costs). I
don't think 50 to 100 units is realistic at this point as that would
require a $2500 to $5000 overhead.
> 2. same question about the pcb .
That depends on the manufacturer you choose. Olimex has a 20%
discount for any subsequent orders of the same board, saving you $5.
Other manufacturers have steeper discounts, but higher starting costs.
> 3. about other things , can you make a detailed list what we need ,
> so we can start checking how much they cost.
Here's an incomplete draft....:
*Two 9V batteries, and a charger.
*Battery connectors
*A two pole on/off switch
*Five electrodes (and gel)
*Connectors for the electrodes
*A female 9-pin dsub connector for the serial port
*A serial cable
*A plastic or wooden box large enough for a euro-board
*Metal plates (solderable) for on-board EMI shielding. RS components
sells factory-made shielding for about $10 each (you need two)
(*Small metal box - half euro-size - for the EEG-amplifiers - would
replace the metal plates)
*Wire connecting all the pieces.
*A programmer cable.
> 4. i would like us to explore alternative ways to build a cheap
eeg .
> for example going to the direction of hires eeg , and other
> directions .just to see how much we can cut the price and cut
> assembly complexity.
Feel free to suggest things to change. I can give you all material
there is on the Hires EEG but I can't do any work on it right now I'm
afraid.
> 5. another issue if were going to the kit idea (which at
> first step seems possible ) is programming . how a person
without
> programmer does this ?
A programmer for the AVR consists in its simplest form of a cable you
connect to the printer port, and a piece of software. The cable has
four parts: A ribbon-cable, a ribbon cable connector, a 25-pin male
dsub connector and a hood for the dsub connector. No electronics.
Please don't get ahead of yourself too much. This design is *way*
behind the ModularEEG in terms of being finished. There are a lot of
pitfalls to avoid... just to give you an idea, there's a list below.
None of those things can be solved on paper.
By the way, how's it going Joerg? Moritz? It would be very nice if
you are finished soon. :-)
Regards,
Andreas
--------
Design problems:
* Noise and distortion: Unknown right now.
* Layout: currently, all signals are routed on the bottom layer. This
is so people can manufacture their own PCB's by hand. Unfortunately,
we might get EMI problems with this. See next point
* Shielding: A few pieces of copper or tin plating, cut to size
requires a lot of mechanical skill to put together (or $20 extra at
RS Components for factory-made shielding). It is not unlikely it is
needed on both sides of the board, since the signals are routed on
the bottom layer.
Another way is to cut the board in two and place the front-stage
amplifiers in a regular metal box, that goes inside the larger
plastic box. This will add about $10, but would be simpler and
sturdier. The layout must be redrawn too (not difficult). Maybe this
is the way to go...
* Battery: There is no low-battery detector. One can be implemented
with two resistors connected to the microcontroller, at the expense
of the decoupling capacitor for the internal reference. It will
decrease noise immunity though.
* New microcontroller: AT90S4433 is nice, but using that would make
this device look a LOT more like ModularEEG. The only difference
would then be in the small details - like dual vs. single power
supply, choice of instrumentation amplifier and filters. Don't want
to infringe on Joergs and Moritz' territory... I already am, it feels
like.
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:43 BST