Multichannel Systems MC_Rack Manual - Manual (Page 129)

MC_Rack Features
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4.11 Real-time Feedback
4.11.1 Real-time Feedback
Introduction
The real-time feedback feature represents a significant improvement in signal detection and
processing. Previously, the digitized signals were processed by the computers main processor,
which involved the operating system and resulted in unpredictable and rather long delays
between the actual event and its’ detection. With the new generation of USB based data
acquisition systems from MCS, online filtering, signal detection and generation of feedback
signals are realized by a Digital Signal Processor (DSP) in the data acquisition hardware.
It is now possible to reliably generate a feedback signal within a time frame of one millisecond
after the actual event.
The main purpose of this feature is to allow the user to generate TTL signals in response to
defined signal patterns detected by one or several electrodes. These TTL signals in turn can control
a stimulus generator (STG) to deliver feedback stimulation to the biological sample. It is also
possible to use the TTL for example, to activate an imaging system, or control a drug application
device.
The real-time feedback function consists of four components: Online filtering, signal
detection, feedback logic, and generation of a digital TTL feedback signal. The filtering
is optional; you can use a high pass, a low pass, or a band pass filter on your data. The signal
detection works either on the raw data or on the filtered data stream. Signal detection works
by an individual threshold that can be adjusted for each electrode. After the signal detection,
the user can define the conditions that will trigger a TTL signal by a feedback logic. Either single
events or event rates on one or several electrodes combined can be set as condition to trigger
a TTL signal. 16 digital output channels are available, each of which can be activated by a
different signal condition. Events from the same electrode can be used in more than one
logical block. The following scheme illustrates the principle of real-time feedback processing.
Limitations
Real-time feedback is available only for advanced data acquisition systems like USB-MEA-
or USB-ME-Systems. It is not available with MC_Card data acquisition or in simulation mode.
Furthermore, a firmware update and MC_Rack version 4.0 or higher is required. Due to
the performance limitations of the Digital Signal Processor (DSP), online filtering and signal
detection are limited to 64 channels at the moment. If you have more than 64 channels, it is
necessary to select a maximum number of 64 channels at a time for real-time processing.
MEA2100-Systems with the exception of the MEA2100-32-System are equipped with
an additional DSP which allows programming from extern. You can feed in individual
adapted signals for your individual designed experiments.