Wednesday, 10 May 2017

usb - RnD on an EEG, Help required, what op-amp?


this is my first post, and I need some help/advice finding the right integrated circuits. I'll start by describing the project background a bit. I've received a fellowship to develop an open source electroencephalograph, the finished hardware will provide a platform for people to develop various creative and therapeutic uses for an EEG system i.e music controllers, game controllers or brain training programs. I want to use an Atmel MCU for the analogue to digital conversion, I'd like it to connect to a computer via USB and I'd also like the unit to be powered by the USB connection. I need help finding a suitable op-amp IC to amplify the signals from the electrodes prior to the MCU. The finished device will be 16 channels, so I'd like to find an IC with multiple op-amps. The electrical activity picked up by the electrodes will be in the region of 200mV and less, so I'll need a lot of gain. Is it possible to adjust the gain of an op-amp circuit with an MCU by using a digital resistor program? It would be nice if the hardware could be reprogrammed to work with various audio and sensor inputs. Any help or advice would be fantastic.


Jim.



Answer



Your average instrumentation amp can easily do 1MHz bandwidth; and your EEG should be no more than 2kSPS. So a multiplexer / Sample and Hold ahead of the the instrumentation amp ought to save you there.


But consider that the amp should be only a few dollars. Is it worth the multiplexing? If you do Surface Mount, the size will be quite minimal.


The Arduino cannot digitise faster than about 10kSPS, so you would need a faster A/D to do 16 channels. Something that can do 12 bits at 100kSPS would be nice. They are also fairly cheap.


Note that for patient safety you need optical isolation on signals, and a good isolated supply (battery or similar). Don't mess with safety in this area - if you need to get a high speed data stream out, build your own isolators or use fibreoptics to transmit the signal.


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