Light Emitting Diodes – Indicator LEDs

Light emitting diodes (LEDs) are a type of diode that is made to light up while forward biased and passing current. Indicator LEDs will be the focus of this page. They are usually 3 – 5mm round through hole components that commonly come in electronics kits.

Basic indicator LED properties

Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom
Rectifier diode and LED schematic symbols and common appearance with forward biased polarity diagram by electronzap electronzapdotcom
  • Series resistor must be used to protect the LED. For most LEDs, the resistor should limit current to no more than 20mA of current for whatever voltage is used.
  • Anode usually has a longer lead than the Cathode as long as they haven’t been trimmed. Cathode often has a flat edge.
  • Many multimeters can test diodes/LEDs. Do not use the diode testing setting while the LED is being powered. LED lights up when the red probe is touching the anode and the black probe is touching the cathode. LED does not light up when red probe is connected to Cathode and black probe is connected to the Anode. Meter will likely tell you the forward voltage as well.
  • Forward biased (FB): Anode more positive than Cathode. LED lights up once forward voltage is reached. Exact voltage is slightly variable. Typically about 1.8V for red LEDs, and about 2.8V for green or blue LEDs.
  • Reverse biased (RB): Cathode more positive than Anode. Best to still keep at low voltages. I avoid going above 9V RB as I had some breakdown (start conducting and being destroyed) somewhere not far above 9V.

Simple LED circuit diagram

Basic electronics LED circuit expectations using a 9V 500mAh battery 470 ohm or 1K resistor diagram by electronzap electronzapdotcom
Basic electronics LED circuit expectations using a 9V 500mAh battery 470 ohm or 1K resistor diagram by electronzap electronzapdotcom

You need a resistor between the voltage source and the LED.

  • 5V power source: 220Ω (two hundred twenty ohm) or more resistance is good to protect an LED.
  • 9V power source: 470Ω or more resistance is good for protecting an LED.
  • 12V power source: 1k (one kilo/thousand ohm) resistance or more is good for protecting an LED.
9V battery with snap wires to power current limiting resistor with LED circuit on breadbard diagram by electronzap electronzapdotcom
9V battery with snap wires to power current limiting resistor with LED circuit on breadbard diagram by electronzap electronzapdotcom
Related topics:

Other basic electronics topics that you should know before moving on to more advanced topics.

555 timer is an integrated circuit (IC). Being an IC, it has complex circuitry combined in a single package with external pins/terminals to connect to other circuitry. You can easily make all kinds of fun circuits with just a 555 timer and the components covered above, so I think it’s a good component to learn next.

Transistors will probably be the most challenging components to learn. Understanding them will help you understand all of electronics much better, and help you the most in being creative while designing your own circuits.

Other topics:

These pages are still being compiled.

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