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Figure A–6
The equivalent circuit of the
external trigger input
Figure A–7
The analog output stage, set
up for a differential stimulus
34
The PowerLab has an optically isolated external trigger input, thus
there is no direct connection between the external trigger ground and
the ground of the device connected to it. This removes ground noise
and current problems, and improves static discharge immunity. In
order for the external trigger to work, though, a voltage must be
applied between the outer ring and the inner pin on the connector.
Applying a voltage to the centre pin won't result in triggering (as it
could on earlier PowerLabs). The equivalent circuit of the external
trigger is basically an LED (light-emitting diode) in series with a
resistor, thus the device driving the external trigger must be capable
of supplying at least 1 mA of current to cause the optocoupler to
work. (The second diode shown below protects the optocoupler.)
Centre pin of BNC
Outside ring
of BNC
The Analog Output
The analog outputs provide computer-controlled variable outputs
(±10 V) that can be used with the Chart and Scope applications either
directly as a stimulator, or to control peripheral devices. All
stimulation voltage is generated by the PowerLab via the output
sockets on the front of the PowerLab (marked Output 1 and Output
2), giving positive, negative, differential, or independent stimuli,
depending on the sockets used and the software settings.
+
From DAC
Ground
–
By default, the outputs are used for complementary (differential)
stimulation, where Output 1 is positive and Output 2 is negative.
When Output 1 is used, a positive stimulus voltage (set up in an
application) gives a positive voltage output, and a negative voltage a
1500 Ω resistor
+10 V
–10 V
+10 V
–10 V
Optocoupler
PowerLab Owner's Guide
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