Multi-channel OpenEEG

Getting the parts

Divide the number of channels you want by 2, and buy that many analogue boards (ie. for 6 channels, 3 analogue boards).  You will still only need one digital board.  The number of channels can be 2, 4, or 6 (not including DRL)

You will also need to buy a 34-pin ribbon cable with as many plugs as you have boards. So 3 x analogue boards + 1 x digital board means 4 plugs.

Preparing the parts

The analogue boards need to be configured as a master and two slaves.

Only one DRL channel

You should only have one DRL channel. You will need to hook the boards together specially for this. Here are various bits of advice which have been collected on this subject:

Jörg Hansmann says in the Analogue schematic: Only insert IC201 on _one_ board when using 2 or 3 amplifier boards.

You should insert the IC201 on the Master, but not the slaves. If you bought the board from Olimex, you can remove this IC from its socket easily.

If you are constructing this yourself, the following parts are not needed on the slave boards either: C212, C216, R213, R218, P201,

For best results, leave IC204 in and wire your multiple analogue boards together at PAD205 (COM). If you are not wiring these pads together, you will not need to insert IC204 on the slave boards.

Jörg says: However there is one serious drawback in deriving the DRL output from many channels: If the user decides to do a session with e.g. 1 channel, _all_ unused EEG inputs have to be connected to VGND. Else the DRL circuit can not work properly.

Jumpering

This can be used to choose Master, Slave1, or Slave2 on each board. This is done by choosing which set of solder jumpers you close. The choices are:

The Olimex boards come hardwired as masters.

Hooking everything up

Follow the usual instructions, except:

• When you connect the analogue boards to the digital board via the (34-pin) ribbon cable, hook all of them together instead of just 2.
• The DRL should be attached to the Master board
• For best results, wire the COM (PAD205) points together