From: Brian Gr (brian_gr_at_hotmail.com)
Date: 2001-12-30 00:22:11
Let's stand back a bit and look at the total differential cost of these twoapproaches:
Approach 1, Modular_eeg
6 Channel A/D converter, microprocessor, rs232 isolation $15.00?
I'm assuming battery power on eeg side and photo isolation for both approaches.
Total $15.
Approach 2, multiple AM modulators feeding sound card line in's
Assume you can drive 2 channels per sound card, although I'd be concerned about many issues to get reasonable resolution.
Per channel costs:
AM modulator per channel, assume some sort of balanced modulator and additional op amps $2.50?
filter, Maxim, as described below $4.50
analog isolation per channel $5.00?
$12 / channel.
Per system costs:
filter clock generator $2.00?
System dependant potential additional costs:
Additional sound card if existing cards aren't full duplex....$10
Extra sound cards for channels 3-6...$10 each
So, to implement a 2 channel system:
AM modulation approach: $24 + $2 = $26
data rate: 10,560 Kbytes / minute, requires considerable additional processing to retrieve samples. (assume 44000 samples / sec / channel, 16 bit samples)
Modular EEG approach: $15
data rate: 168 Kbytes / minute (assume 200 samps/sec, 6 channels, 1 channel overhead (14 bytes transmitted per sample, that's about 28000 baud serial bandwidth, same format used for 1 through 6 channels)) requires minimalprocessing to retrieve samples.
4 channel system:
AM: $48 + $2 + $10 (extra sound card) = $60
data rate: 21,120 Kbytes / minute (good luck)
ModularEEG: $15
data rate: 168 Kbytes / minute
6 channel system:
AM: $60 + $2 + $20 (2 extra sound cards) = $82
data rate: 31,680 Kbytes / minute (forget it)
ModularEEG: $15
data rate: 168 Kbytes / minute
Add $10 to each AM system if existing PC sound card is not full duplex (assuming sound feedback is desired).
The AM system will take much more board real estate, especially when it's expanded beyond one channel.
The AM modulators will undoubtedly need complex calibration and will rely on sound card performance for system accuracy. These are all expensive compared to the modular EEG approach and will result in less consistency and accuracy.
The AM modulator approach will require much more powerful PC processor requirements (processor utilization to extract data) and this requirement will increase as channels are increased.
I'd much rather have the PC being able to add value to the system (such as drive more graphics, L/S or magnetic feedback stimulation) instead of reading multiple sound cards and trying to determine what's
Can anyone think of examples of where this approach (AM modulators and sound card inputs) have been used?
Have a happy new year!
Brian.
----- Original Message -----
From: JimmyB_101
To: buildcheapeeg_at_yahoogroups.com
Sent: Saturday, December 29, 2001 4:30 PM
Subject: [buildcheapeeg] Re:(Semi)OT> Amplitude modulation
>
> It's not difficult to make fancy filters (with the right synthesis-
> software), but they cost more money. Also, if you know nothing of
> filters, but need one, you can buy 8th order switched-capacitor
> lowpass filters for $9. Just add a clock-signal - the frequency
> decides what cutoff frequency you get. Can't get any easier than
> that. :-)
>
There may be some Maxim units for about half that price.
(free samples in any case)
Yahoo! Groups Sponsor
ADVERTISEMENT
To unsubscribe from this group, send an email to:
buildcheapeeg-unsubscribe_at_egroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST