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Two onboard microphones (U2 and U5) can be used in applications 
requiring audio input or involving audio signal phase difference 
measurements. When the microphones are used, the input gain level of 
each microphone should be set to the microphone level setting described 
in the 

 section.

Ensure that line level audio signals are not connected to the audio input when the 

NI SPEEDY-33 is configured for microphone level. It is possible to damage the audio input 
circuitry by overdriving the input.

The onboard microphones are directly connected to the audio input 
conditioning circuitry, unless an external microphone is connected at 
the stereo input port (U11), as described in the 

section. If an external microphone is connected, the onboard microphones 
are disconnected from the input circuitry by mechanical disconnect.

Eight memory-mapped LEDs are located on the NI SPEEDY-33 for 
general-purpose output. The LEDs are enabled by writing a 1 to the 
appropriate bit of the LED port. The LED output state is echoed on pins on 
the simple expansion digital I/O connector (J11), as described in the 

There are eight memory-mapped general-purpose switch inputs on the 
NI SPEEDY-33. These switch inputs are accessed by the DSP through 
reading the appropriate bit of the switch input port. The switch inputs are 
connected in parallel to pins on the simple expansion digital I/O connector 
(J11). All switches should be in the OFF (open) position when connecting 
the expansion digital I/O connector, as described in the