BSL PRO 4 Manual - Biopac

140 BSL PRO ManualThe channel selected in the Output Channel section determines which digital channel the pulse will be sent to.The digital channels range from 1 to 8 (D1 through D8. In the sample dialog shown, the digital pulse is sentover I/O line D1.Digital channels have two levels, 0 Volts and +5 Volts. When the signal transits from 0 Volts to 5 Volts, an“edge” is created and since the signal is going from low to high, this is referred to as a positive edge.Similarly, as the signal transits back from 5 Volts to 0, a negative edge is created. These transitions or edgescan be used to trigger external devices when an analog signal level meets certain threshold criteria.The Threshold Function option sets the criteria for the Control channel. You can specify threshold conditionssuch that the digital I/O line goes to +5 Volts when the conditions are met, or you can program the digital lineto go to 0 Volts when the threshold conditions are met. Threshold conditions can be set so that either (a) thedigital line is switched when the value of an analog channel exceeds a specified value or (b) the digital line isswitched when an analog channel falls within a given range. BSL PRO also allows you to create a single levelthreshold or a “wide” threshold.Tip To use test conditions more complicated than simple thresholding, combine the conditional tests ofExpression calculations with the Control channel to change digital output based on the Expressionresult.For example, suppose you want to set a Control channel to switch digital line 5 from low to high wheneverthe signal for Calculation channel one (C1) exceeds 85 BPM. Set the source channel to C1 and the output toD5. Select the upper left graph in the control dialog and set L2 and L1 to 85, as shown:Control dialog and graph showing result of BPM control exampleAs you can tell from the preceding graph, there are a number of instances where C1 (heart rate) exceeds 85,usually for a short period of time. When it does drop below 85, it appears to return to a value greater than 85within a second or two. In instances such as this, it might be useful to “widen” the threshold so that the digitalline is triggered whenever the input value is greater than 85, but the signal must drop significantly below thethreshold value before the threshold is reset.Visit the online support center at www.biopac.com