From: dremelz (dremelz_at_yahoo.com)
Date: 2001-12-19 21:07:55
--- In buildcheapeeg_at_yahoogroups.com, Moritz von Buttlar <info_at_baltic-microsolutions.de> wrote:
>At 19:34 18.12.2001 -0800, you wrote:
>>michalchik_at_aol.com wrote:
>>
>> >> following the simple biosemi input stage ...
>> > Do you care to share the schematics?
>>
>>The amplifier schematic is here
>>http://www.biosemi.com/publications/eegfig3.gif
>>
>>I will follow Joerg's ModularEEG digital board
>>schematic for power supply and isolation. I
>>think I will try DS275 level converters.
>One little disadvantage of the DS275: I think it needs a 5V supply.
>I was
>always thinking
>about battery operation using 4 NiMh rechargeable batteries
>(4*1.2V=4.8V).
>In this case
>the DS275 might not work. The DS276 is for lower voltages, but it
>doesn't
>allow full speed
>serial communication. But of course in your system where you'll
>always have
>+5V the
>DS275 is just perfect.
I think that the analog to digital conversion is based upon AC biased
at 2.5V (i.e., 0 to 5V). Of course, you can always adjust that. Why
not just add a battery of two, and to get stable signals and
conversion, feed the supply through a low power (<50ma) 5V regulator
chip to avoid power supply voltage drop that occurs when the
batteries approach depletion. Or were you thinking of regulation at
less than 5V?
You know that the DS275 is on the RS-232 side of the 6N139
optoisolators. You can use RS-232 control signal power stealing with
a low power (<50ma) 5V regulator chip to power the DS275 (you may
need two of the DS275 chips if you use full-duplex to simplify
handshaking) and to power one of the 6N139 optoisolators. The other
6N139 would be powered by the EEG power.
If you use RS-232 control signal power stealing to power the RS-232
side and batteries to power the EEG side, then you can eliminate the
DC-DC convertor which has a much lower level of isolation.
See my post on this same mailing list with the following subject
header:
New member/BM/6N139/DS275/Isolation/Entrainment/CES/Migraine
dated Sunday, Dec 16.
Regards,
Jeff
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