From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-02-12 20:08:03
Dear Andreas:
I believe your choice is an excellent one. The three batteries is a simple, foolproof and fast solution. The KISS principle.
The more complicated or "better" solutions can be addressed "after" this works.
It may not be "necessary" to regulate the analog power supplies, but regulators are cheap and reduces another variable.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: sleeper75se
To: buildcheapeeg_at_yahoogroups.com
Sent: Tuesday, February 12, 2002 7:13 AM
Subject: [buildcheapeeg] Re: Loose ends: Power
Hi,
I won't get into the parallel discussion about how biofeedback should
or should not work, so let's return to the original subject of this
thread. ;o)
All of your suggestions + some research (aka websurfing ad nauseum)
resulted in "Keep It Simple Stupid". :-)
I'm afraid I don't have the time nor the skill or inclination to
design a low-noise switched power supply from scratch, and the local
Traco-distributor wouldn't sell me less than 20 medical-grade DC/DC-
converters. I also really like "real" dual power supplies. Virtual
ground is nice, but I don't dare using it for this design.
So I've decided on the HAL-way, because it is the easiest: three 7.2
or 8.4V 150mAh NiMH batteries + linear (LDO) regulators will power
the EEG.
The first battery is used for positive analog power, the second for
negative analog power, and the third for digital power. I estimate
the current consumption is around 20mA per battery with four EEG
channels, so you get a running time of around 7 hours with 150mAh
batteries.
If someone just wants to play around, they can buy regular 9V
batteries instead (good for probably 10 hrs), while the enthusiast
can get three 12V, 2Ah rechargeable lead batteries that can keep the
thing running for 100 hours.
Also, if you add clamping diodes to the ADC inputs, it is possible to
run the amplifier on unregulated (but filtered) +/-12V.
Costs:
3x9V (non-rechargeable): $12
3x8.4V (NiMH): $30
3x12V (Pb): $70
Charger: $15-100
Basically, it is up to the individual how much to spend, anything
from $12 to $170.
Doug, I know that you would like to use a single +5V power source. It
can be done with a low-isolation (1kV typically) DC/DC converter.
There are several types that generate unregulated dual voltages from
a single input voltage. Regulation is then done by linear LDO
regulators and passive LC-filters. All the magic happens inside the
converter so you don't have to be an analog expert. Here's what I
have in mind: http://www.cdncl.com/cd/products/dc_converters/nmh.asp
Application notes describing what the filters should look like are
here:
http://www.cdncl.com/cd/products/application/dcdc_converter.htm#Filter
ing
Sorry for the fragmented post, I'm just writing down a bunch of ideas.
Regards,
Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:38 BST