Learn Electronics

Learn Simple Circuts by Example

The Basic Switch

This simple circut is very basic, and is used in almost everyday electronics.
When the switch is closed, current from the power supply travels to ground thru the resistor and switch.
Without the resistor in this circut, the battery will overheat from all current possible flowing from the battery with no resistance, hence a short circut.
Current will travel from the point of most negitive to the point of most posistive. In this case, from ground, thru resistor, switch, then back to the posistive side of the power supply, indicated by the "V" shaped symbol.
Resistors reduce the current flow to safe level.

The Led

The LED (Light Emitting Diode) is a light source that emits protons when current is flowing thru it, with a voltage around 2 volts.
A resistor has to be present in series to limit the flow of current if the power supply is over 2 volts.
LED's have a certain voltage drop across it, say around 2 volts when powered. If your powering this device with a 9 volt cell, the other 7 volts must be "lost" in the resistor, and 2 volts for the LED, to equal the supply.
Most LED's will not illuminate without the voltage being at least 1.3 volts or so.

Resistors in Parellel

The components are now labeled using the standard format.
r1 and r2 are resistors, sw1 is a switch, and the "+" represents the power supply.
Resistors are measured in Ohms, and the values here will be 10,000 ohms or 10k a piece.
When the switch is open, all the current can only flow thru the resistor and LED and back to ground. With the switch closed, current flows thru r1 and r2 , since they are wired in parallel. Two paths for current flow is now present.
The LED does not get any brighter due to r2 not being in circut with the LED, even though the power supply is has doubled the amount of current.