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
- 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
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.
Other basic electronics topics that you should know before moving on to more advanced topics.
- Electronic component appearance and schematics – Commonly used through hole versions
- Electronic circuit basics
- Voltage sources for electronics basics
- Multimeter measuring voltage
- Resistor component – Learning electronics resistors
- Light Emitting Diodes – Indicator LEDs
- LED circuit -Lighting a Light Emitting Diode
- Resistor limiting current – Ohms law
- Multimeter measuring current
- Wattage – Electrical Power unit
- Resistors connected in parallel
- Series resistors
- Voltage divider – Setting a fractional voltage
- Resistor color code
- Diode – Rectifier
- Trimpot – Trimmer potentiometer – Voltage divider – Variable resistor
- Capacitor component
- Capacitor RC time constant
- Voltage ramp Demonstrated using a capacitor.
- LM334 three terminal adjustable current source not a common component. I use for an easy current source in many circuits.
- Switch NOT logic gate – digital signal inverter
- Switch OR gate – LED circuit
- Switch AND gate – LED circuit
- Switch based NAND logic gate – LED demonstration circuit
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.
- 555 Timer IC This particulars of this integrated circuit covered on this page make a lot more sense after you study the basic circuits that follow.
- 555 timer bistable mode – Flip flip basic circuit
- 555 timer monostable mode – One shot
- 555 timer astable multivibrator mode – Flashing LEDs
- 555 timer schmitt trigger logic inverter – NOT gate
- 555 timer LDR controlled astable multivibrator mode LED flasher circuit
- 555 timer – Buzzer output – Astable multivibrator mode – Light dependent resistor LDR controlled circuit
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.
- NPN BJT switch circuit – Bipolar Junction Transistor – 2N3904
- PNP BJT switch – Bipolar Junction Transistor – 2N3906
- NPN BJT emitter follower circuit – transferring a voltage minus a diode drop
- PNP BJT emitter follower circuit – Transferring weak signal voltage with a diode voltage shift
- NPN BJT current source – Bipolar Junction Transistor – 2N3904
- PNP BJT current source – Bipolar Junction Transistor – 2N3906
- Schmitt trigger – NPN BJT
- Zener diode component – voltage reference – regulator
- Voltage doubler circuit fragment- Capacitor charge pump – Some V loss
- 7805 5V positive voltage regulator IC
- Battery voltage state of charge SOC – From fully charged to discharged
These pages are still being compiled.
Topics covered more quickly:
- Brief trimmer potentiometer trimpot variable resistor voltage divider circuit fragment
- Brief capacitor charge and discharge through LEDs circuit
- Brief 555 bistable mode flip flop alternating LEDs circuit
- Series batteries for a higher voltage
- Parallel batteries for more current
- Series resistors
- Parallel resistors
- Quick NPN BJT switch circuit – Bipolar Junction Transistor
- Brief PNP BJT switch circuit – Bipolar Junction Transistor