User manual

122 Appendix A: Using the EyeLink 1000 Analog and Digital Output Card

7.3.2 Connections to Analog Card

The analog card is supplied with a connection cable and screw terminal

connection board. Analog outputs and digital inputs and outputs are available

from this card (see the document included with the screw terminal board for

which terminals correspond to the analog outputs, digital inputs and outputs,

and ground or +5V). It is up to each user to determine how to connect and use

the analog output connections for their applications. Connections to the analog

outputs will depend on what these outputs are connected to - typically this is

another computer with an analog input card.

7.3.3 Noise and Filtering

It is very important to make sure these connections are made in a way that does

not introduce noise into the data, so connections between the analog output

terminals and the analog input terminals must be as short as possible. If the

analog input device does not have filters, it may be helpful to add a conditioning

filter to each analog connection. A 470 ohm resistor between the output and

input, and a 0.1 microfarad capacitor from the input to ground, will filter out

most noise sources while not affecting the analog signals (this is a 3.4 KHz low

pass filter, which should settle to 1% in 220 microseconds).

7.4 Digital Inputs and Outputs

The digital ports are configured by the EyeLink software with A0-A7 and B0-B7

as inputs, and C0-C7 and D0-D7 as outputs. A digital-only card is available

when analog output is not required.

Digital outputs may be set by the write_ioport command, which may be

issued though the link or by a button or initialization file command. The port

address for the C and D ports on the EyeLink analog output card are 4 and 5,

respectively. Digital outputs may also be reserved for EyeLink tracker functions,

and writing to these bits has no effect. For example, when analog output is

enabled, the data output D7 is used as a strobe output to indicate when new

analog data is available.

The digital inputs may be used as buttons and as input port bits, which may be

recorded in the EDF data file, or sent as samples via the Ethernet link. Button

inputs may be connected to a digital output (such as a printer port) from a

control computer, and assigned functions such as starting and stopping

recording, or used as synchronizing marks in the data file. When used as a real

button for participant response, the button is typically connected to ground, a

10 K ohm resistor should be connected from the input to one of the +5V