Datasheet

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When sizing out a current-limiting resistor, look for two characteristic values of the LED: the typical forward voltage, and the maximum forward current. The typical forward
voltage is the voltage which is required to make an LED light up, and it varies (usually somewhere between 1.7V and 3.4V) depending upon the color of the LED. The
maximum forward current is usually around 20mA for basic LEDs; continuous current through the LED should always be equal to or less than that current rating.
Once you’ve gotten ahold of those two values, you can size up a current-limiting resistor with this equation:
V is the source voltage – usually a battery or power supply voltage. V and I are the LED’s forward voltage and the desired current that runs through it.
For example, assume you have a 9V battery to power an LED. If your LED is red, it might have a forward voltage around 1.8V. If you want to limit the current to 10mA, use a
series resistor of about 720Ω.
Voltage Dividers
A voltage divider is a resistor circuit which turns a large voltage into a smaller one. Using just two resistors in series, an output voltage can be created that’s a fraction of the
input voltage.
Here’s the voltage divider circuit:
Two resistors, R and R , are connected in series and a voltage source (V ) is connected across them. The voltage from V to GND can be calculated as:
For example, if R was 1.7kΩ and R was 3.3kΩ, a 5V input voltage could be turned into 3.3V at the V terminal.
Voltage dividers are very handy for reading resistive sensors, like photocells, flex sensors, and force-sensitive resistors. One half of the voltage divider is the sensor, and the
part is a static resistor. The output voltage between the two components is connected to an analog-to-digital converter on a microcontroller (MCU) to read the sensor’s value.
S F F
1 2 in out
1 2 out