PAGE 062 OF 150 · DRIVING WITH SWITCHES & TRANSISTORS
Slide Switch and Toggle Switch Basics
Poles and throws describe how many circuits switch.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Switch types
- SPST: one on-off path, the simplest light switch.
- SPDT: one input switched between two outputs, handy for choosing one of two LEDs.
- DPDT: two separate SPDT switches operated together.
Wiring
Place the switch in series with the LED branch, either before or after the resistor. In low-voltage circuits the position does not change how it works.
Ratings
Check voltage and current ratings, and choose a switch rated well above the load. Small slide switches often handle only a few hundred milliamps.
REMEMBER
A transistor lets a tiny signal control a much larger LED current.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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