Marker channel

Last modified by Iris Spruit on 2023/08/04 16:02


Markers, i.e. numeric values can be sent to the Biopac system, to mark significant moments in the recording, which are required for analyzing the data. Markers that are sent to the Biopac system through the parallel port, Eva, or UsbParMarker, consist of 8 bits. Each of these bits can either be on or off and this allows for sending numeric values 0 to 255 (e.g. value 1 is 0 0 0 0 0 0 0 1 in bits, value two is 0 0 0 0 0 0 1 0, and value 255 is 1 1 1 1 1 1 1 1, see here for more info on binary numbers.).

To record markers in AcqKnowledge, the 8 bits of data can need to be setup as 8 digital channels in the AcqKnowledge template. Then, a calculation channel needs to be setup that transforms the 8 bits of information back to a decimal number. See below the steps necessary to add a Marker channel in AcqKnowledge.

See for more information on sending markers from stimulus presentation software the pages Sending Markers in E-Prime and Sending Markers in OpenSesame and the Markers and Events page for more information on markers in general.


Click on the Digital tab

Select the Acquire checkboxes of channels D8 to D15 (those are the 8 digital input channels). Note that it will not work when other digital input channels are selected, i.e. D0 - D7.

To convert these 8 bits of data to one value, we’ll need to add a calculation channel

Go to the Calculation tab. Calculation channels are used for online computations and transformations of other channels. Note that calculations can always be done after data collection, but to see the channels online, they need to be set up in the AcqKnowledge template.

Select Acquire of the first channel (C0).

A window automatically pops up.

In Preset, select Expression

Source channel can be left to the ECG channel

Make sure the Plot checkbox is checked

Click OK


Enter the Label: "Marker"

Enter the calculation for the marker value in the input box:

((1*D8) + (2*D9) + (4*D10) + (8*D11) + (16*D12) + (32*D13) + (64*D14) + (128*D15)) / 5

Click OK

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