ELECTRICAL AND ELECTRONIC DEVICES
To move beyond cells and lamps, we need to introduce some more electrical and electronic devices and their symbols.
Push button. A normally open push button conducts electricity when it is being pressed, otherwise it's an open circuit. Switch. Has an on and an off position. Conducts when it's on and is an open circuit when off.
To see how devices combine, the cell and lamp circuit from above is recreated below with the addition of a switch to turn the lamp on and off. The switch works, just like it looks like in the diagram, by making or breaking a connection which completes the circuit or leaves it open. An important observation is that it doesn't matter whether the switch is on the connection from the positive side of the battery to the lamp or on the negative side. As long as it can disrupt the circuit somewhere, it will work as a switch.
|Lamp Circuit with switch|
More sophisticated circuits require more complex components. Some more are presented below.
|Potentiometer. A variable resistor. Often connected as a voltage divider to create variable voltages when used as a rotational position sensor.|
|LED. Light Emitting Diode. Common indicator in electronics. Produces a lot of light for not much current. But will very quickly (perhaps instantaneously) burn out if too much current is allowed to flow in it. Like any diode, has very low resistance in its conducting direction, so a resistor in series with it to limit the current is usually a requirement.|
|Photoresistor. A resistor with the useful property that its resistance changes depending on how much light it is receiving. Photoresistors can have a quite impressive resistance range, for example from a few million ohms (M) in the dark to under a hundred ohms in bright light. One possible disadvantage is that their reaction time is in the order of 100ms - too slow for many applications.|