Tutorial: External Trig

This example will take off from the basic setup found in ttBasic0.mat.

Data acquisition and stimulation will be synchronized to some external event, that cannot be controlled from Mr. Kick. For the purpose of illustration we'll use the H-reflex elicited during walking. The step cycle will vary over time and we need a way to make sure that stimulation is applied at the same point in every step cycle.

Common Settings

The only difference from the basic setup is the way data acquisition and stimulation is trigged. As a result all settings regarding -

• Acquisition
• Analog Input
• Classification
• Event Timing
• Analog Output (Off)

will be the same. They shall not be discussed further here.

External Digital Trig

Assume we have a digital signal, that indicates when a specific point in the step cycle is reached. A very simple example could be a foot switch indicating heel contact. We'll use that signal to trigger both data acquisition and stimulation.

Trigger

A digital trigger may be applied to any of the six PFI-inputs #0 through #5 - say we use input #1. In the DAQ Trigger SetUp we set the Mode - Source control to Ext. Digital PFI-1. If we want both data acquisition and stimulation to start on on the rising edge of the digital input we'll set the Edge control to Rising.

It may not be appropriate to stimulate in every step cycle, so we'll reduce that to approx. every fifth step. Assuming a step cycle lasts 1 sec. we set Refractory to 4.5 sec.

These settings are available from ttExTrg0.mat.

External Analog Trig

Instead of an digital signal we might have an analog signal indicating the actual point in the step cycle. This could be a goniometer placed at the ankle or knee joint. Both data acquisition and stimulation should then start when a specified level is reached in the rising or falling analog signal.

Trigger

An analog trigger can only be applied to PFI-input #0. In the DAQ Trigger Setup we set the Mode - Source control to Ext. Analog PFI-0. If we want both data acquisition and stimulation to start on on a rising signal we'll set the Edge control to Rising.

The level at which to trig is specified in the Level control. It's set as a voltage measured at the PFI-0 input at the MIO-board. Hysteresis may be added to avoid false triggers. We could choose 2 V with a hysteresis of 160 mV. You may have to adjust both values to achieve the precise trigger point you want.

We'll stick to a Refractory of 4.5 sec in order to stimulate only every fifth step.

These settings are available from ttExTrg1.mat.