4.2 Additional Requirements for Signal Conditioning

There are many other uses for the signal conditioning circuitry depending on the particular HCI application. Some of these are:

Signal isolation

In many applications it is necessary to isolate the sensor from the power supply of the computer. This is done in one of two ways: magnetic isolation or optical isolation. Magnetic isolation is primarily used for coupling power from the computer or the wall outlet to the sensor. This is done through the use of a transformer. Optical isolation is used for coupling the sensor signal to the data acquisition input. This is usually done through the use of a light emitting diode and a photodetector. This can be integrated into a single IC package such as the 6N139.

Signal preprocessing

Many times it is desirable to perform preprocessing on the sensor signal before data acquisition. Depending on the application, this can help lower the required computer processing time, lower the necessary system sampling rate, or even perform functions that will enable the use of a much simpler data acquisition system entirely. For example, while an accelerometer system can output a voltage proportional to acceleration, it may be desired to only tell the computer when the acceleration is greater than a certain amount. This can be accomplished in the analog signal conditioning circuitry. Thus, the data acquisition system is reduced to only having a single binary input (no need for an ADC).

Removal of undesired signals

Many sensors output signals that have many different components to them. It may be desirable or even necessary to remove such components before the signal is digitized. Additional other signals may corrupt the sensor output. This ``noise'' can also be removed using analog circuitry. For example, 60Hz interference can distort the output of low output sensors. The signal conditioning circuitry can remove this before it is amplified and digitized.