The primary thing that resistors do is limit current (moving charges). The current (I) in amps through a resistor is the voltage (V) across the resistor divided by the resistor’s resistance (R) in ohms. I = V/R
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Always keep in mind that while passing current, resistors get hot. The recommended maximum wattage rating of most resistors is 1/4W, but it is still recommended to stay below 1/8W as much as possible. Calculating the wattage (P for power) in watts, of any component, involves taking the voltage (in volts) across it and multiplying that by the current (I) (in amps) flowing through it. P = VI
Usually schematic diagrams will show a safe resistor value to use.
- I = V/R (current equals voltage divided by resistance). Ohms law formula for current from a certain voltage and resistance.
- Voltage (V) across the resistor.
- Current (I) flows through the resistor.
- Current has a linear relationship (straight line on a graph) with resistance for a given voltage. Assuming that the voltage stays the same. Using half the resistance will double the current. Twice the resistance will result in half the current.
The relationship between voltage, resistance and current is known as Ohms law. Here are the 3 main Ohms law formulas.
Common values diagram:
- The three uneven length lines on the right side of the resistor indicates 0V ground (negative side of a DC supply).
- The voltage on the left side of the resistor indicates the supply voltage (positive side of DC supply).
- The supply voltage (Vcc) and 0V ground is the voltage difference across the resistor. So 5 volts across the resistor is considered to have +5V on one side and 0V (ground) on the other side.
- 1/4W (0.25W) maximum is a common value resistor. It is still recommended to keep them below 1/8W (0.125).
- Be aware that any other components in series with the resistor will take away some of the voltage from the resistor. Semiconductors tend to drop a certain amount of voltage while resistive components divide up the voltage based on their percentage of the total resistance.
Clicking the links to watch videos directly on YouTube helps a lot!
Diagram used in video
If you really like this video/diagram format, here are some links to the next topics of the series.
- 002 Diodes especially LED-rectifier forward-reverse bias
- 003 Diodes-Zener voltage regulator-full wave bridge rectifier-polarity indicator
- 004 Voltage dividers-trimpot-LDR light dependent resistor-fixed resistor
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.
Circuits covered more quickly series:
- Brief switch controlled indicator LED circuit
- Brief polarity indicator LEDs circuit
- Brief capacitor charge and discharge through LEDs circuit
- Brief capacitor charging RC time constant demonstration circuit
- Brief 555 bistable mode flip flop alternating LEDs circuit
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