From: Joerg Hansmann (jhansmann_at_g...)
Date: 2001-02-05 23:06:02
Hi,
----- Original Message -----
From: Moritz v. Buttlar <info_at_baltic-microsolutions.de>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Sunday, February 04, 2001 4:56 PM
Subject: [buildcheapeeg] changing the design for battery power and Irda
>
> Hi !
>
> I´m currently trying to add to Joergs design the following options:
>
> - battery operation (4 mignon cells, rechargeable, 4.5-6V, operation >12 hrs)
> I want to connect the battery directly to the circuit without voltage
> regulation. Or is this a bad idea ??
The AT90S4433 has a absolute maximum rating for Vcc of 6.6V.
That means theoretically, if this voltage is exceeded only a fraction of a second
the chip will be damaged or lose permanently performance (i.e. more current uptake,
noise of the analog part etc.).
1)Will it be guaranteed that with full loaded bateries the 6.6 V will _never_ be
exceeded ?
What happens, if someone uses rechargeable alkaline batteries instead of
NiCad-accus ?
2)Another point is calibration voltage generation: It depends on stabilized Vcc.
However Vcal could be (with some circuit change) derived from the reference
voltage source.
If point 1 and 2 are considered I see no reason against not using unstabilized
battery voltage.
BTW. How much voltage drop has a low drop voltage regulator and how much supply
current does it need ?
> - Irda communcation. I´m currently looking for parts. Speed up to 115kbauds,
> distance 1-2m. Joerg: is this fast enough ??
For EEG only (6 AD-channles + 4 bit switches) 56200baud unidirectional will
be sufficient.
> The components will cost <10$. I´ll also add a circuit diagram for a
> RS232<-->Irda interface for all the people who don´t have irda in their pc.
> I first wanted plastic fibre, but I think Irda has the advantage of most
> modern notebooks having already been equipped with Irda.
> It can be updated later for 4Mbps operation !
How shall that be done ? AT90S4433 UART is limited to 115kbaud ...
> - the design will consist of 2 circuit boards: analog and digital.
> This allows an update of the different parts independently. Also different
> versions, e.g. dc-dc converter and regular rs232 for people who prefer that.
>
> The goal is to improve safety of the design. Please write me if you have any
> suggestions.
Irda data transmission should get a checksum (e.g. 16bit CRC) at the end of
each data block to check transmission quality.
CU
Joerg
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:29 BST