10
High Intensity, Single Signal, Multi-positional Stimulation
In experiments where the subject will not be receiving more than one frequency
of stimulation at any one time, it is more practical and economical to use a single
amplifier capable of high voltages since multi-channel high-voltage amplifiers are very
expensive, and generally use step-up transformers which cause very non-linear
behavior. In this case a computer-controlled switch box is used to relay source to the
areas to be stimulated (Fig. 5).
The control box is capable of delivering up to eight channels of tactile
stimulation. It receives eight bit instructions from a computer through a DB25 port, and
receives the signal for driving the piezoelectric bending actuators through a pair of
banana plug jacks. Each pair of banana plug jacks drives four channels, allowing two
different signals to be used, or the same signal can drive all eight channels if the pairs
are jumpered. Each channel can be manually activated by lighted buttons and
individually attenuated by potentiometers, providing a simple way to calibrate the
device.
The operation of the box is simple. The instruction byte is received through the
activation buttons to a 12-volt, eight-bit line driver. When the buttons are depressed
the line driver receives the instruction byte, when a buttons is pressed the line driver
instead receives a "high" signal. Each output of the line driver is connected to the 12-
volt activation pin of a 250-volt relay. The relays themselves Connectthe input signal to