UART to USB interface chips (e.g. the FTDI 24x series)
The MAX232 chip converts 0 to 5 V digital logic voltages (“TTL”) to +- 12 V RS-232 voltages.
“There are also little modules available which have the complete USB/Uart interface on them. These could be plugged into the digital board. They are available from e.g. http://dontronics.com/ .”— Moritz
$19.95 USB to RS232 interface board
http://www.sparkfun.com/shop/index.php?shop=1&itemid=404
Another USB interface chip:
TUSB3410
http://limeybrit.com/eeg/images/tusb3410.png
http://limeybrit.com/eeg/images/
“the TUSB3410 actually has a 8051 processor inside”—James
It would be kinda nifty to power the EEG off USB power (rather than using yet another cable), but USB only provides 100 mA default, 500 mA maximum.
(How much power do we really need? Perhaps that’s already enough?)
AKM 16-bit audio-to-USB chips: ak5370 and ak5371
(mono and stereo)
http://www.asahi-kasei.co.jp/akm/en/product/ak5371/ek5371.pdf
only need a voltage regulator and a few resistors and capacitors (in particular, does not need a microprocessor) to connect a standard microphone to a standard PC USB port.
Minor concern: The best isolation techniques digitize the signal on the patient side, then pass the bits over a (digital) optical isolator to the computer side. Having everything all-in-one is nifty, but to put the isolator in the “right” place requires breaking the chip in half. work-arounds: (a) use (analog) optoisolator between patient and the chip (these exist, but are they precise enough ?); (b) use some sort of opto-isolating USB repeater between the chip and the PC (does this exist ?).
FT232BM USB to RS232 converter chip
