The term **220-R** typically refers to a **220 Ohm Resistor** (where 'R' stands for Ohms). This is one of the most fundamental electronic components used in circuit design, particularly for current limiting and voltage division. ### 1. Technical Specifications The standard 220-R resistor usually falls under the following technical categories: | Feature | Description | | :--- | :--- | | **Resistance Value** | 220 $\Omega$ (Ohms) | | **Color Code** | Red, Red, Brown (for 5% tolerance) | | **Common Power Ratings** | 1/4W (0.25W), 1/2W, or SMD (0805/0603) | | **Tolerance** | Usually ±5% (Gold band) or ±1% (Brown band) | | **Material** | Carbon Film or Metal Film | --- ### 2. The Color Coding System For a through-hole 220-R resistor with 4 bands, the colors are interpreted as follows: | Band Number | Color | Value/Multiplier | | :--- | :--- | :--- | | **1st Band** | Red | 2 | | **2nd Band** | Red | 2 | | **3rd Band (Multiplier)** | Brown | x10 | | **4th Band (Tolerance)** | Gold | ±5% | **Calculation:** $22 \times 10^1 = 220$ Ohms. --- ### 3. Common Applications The 220-R resistor is frequently used in these scenarios: * **LED Current Limiting:** When connecting an LED to a 5V source (like an Arduino), a 220-R resistor is the "standard" choice to prevent the LED from burning out. * *Calculation:* $(5V - 2V_{forward}) / 0.015A \approx 200\Omega$. * **Pull-up/Pull-down Resistors:** Used in digital logic to ensure a pin reaches a known state, though 10k resistors are more common for low power. * **Protection:** Acting as a small buffer to protect sensitive IC pins from minor over-current spikes. --- ### 4. Power Dissipation Warning Before using a 220-R resistor, you must check the power (Wattage). Using **Ohm's Law ($P = V^2 / R$)**: If you connect a 220-R resistor directly across a 12V power supply: $P = 144 / 220 \approx 0.65W$ If you use a standard **1/4W (0.25W)** resistor in this scenario, it will **overheat and fail**, as 0.65W exceeds its rating. ---