Page 73 - Handbook of Biomechatronics

68 Jeff Christenson

Fig. 8 (A) Example of a button. (B) Circuit diagram showing when a button is open.
(C) Circuit diagram showing when a button is closed.

3.1 Mechanical Button
Perhaps, the simplest of electrical sensors, mechanical buttons (Fig. 8) are
useful for sensing user intent. There are two main types of buttons: on/
off and multistate switches (Digikey—Pushbutton-Switches, n.d.). In each
case, a button either closes or opens a circuit to indicate intent of the user.
An on/off button will switch between on and off. Some on/off buttons
will remain in a certain state until an input is applied. Then, the button
switches to the opposite state and remains in that state until an input is again
sensed. Other on/off buttons remain in a certain state and will only switch
when the input is sensed and will return to the original state once the input is
removed.
Multistate switches are those buttons which have more than two states.
There are many different types of latching states which are useful for
selecting different inputs or modes in a device.
Mechanical buttons are different than the capacitive buttons which
are found on touch screens such as cellphones, iPads, and many tablets.
Capacitive buttons will be discussed in Section 3.8.
In Jacob’s new prosthetic system, you specify an on/off button to turn on
and off the device. You consider where to place the button to minimize
accidental on/offs.

3.2 Potentiometer

A potentiometer (Fig. 9) is an electrical device which provides a unique
resistance with an associated position. As the potentiometer dial is turned,
a wiper moves along a variable resistor such that the resistance of the
device changes, which varies the sensor voltage. It is the practical applica-
tion of a voltage divider (https://www.merriam-webster.com/dictionary/
potentiometer, Accessed 21 August 2017).