How do you determine the size of a resistor?
We’ll use the following formula to determine the resistor value: Resistor = (Battery Voltage – LED voltage) / desired LED current. For a typical white LED that requires 10mA, powered by 12V the values are: (12-3.4)/. 010=860 ohms.
How do I choose a pulldown resistor?
A rule of thumb is to use a resistor that is at least 10 times smaller than the value of the input pin impedance. In bipolar logic families which operate at operating at 5 V, the typical pull-up resistor value is 1-5 kΩ. For switch and resistive sensor applications, the typical pull-up resistor value is 1-10 kΩ.
How many ohms should a pull-down resistor have?
Pull-down resistors are a little more critical because of the low input voltage level, VIL(max) and the higher IIL current. The use of 100Ω pull-down resistors are the most common but they can range in resistive value from 50 up to 1k ohms.
What size load resistor do I need?
Calculating the Size of the Load Resistor: B = The size of the LED light bulb (in watts). Using Watt’s law and difference between the filament light bulb and the LED light bulb (in watts) calculated above, we can find the current (amps) needed to mimic the filament light bulb.
What resistor do I need to drop 12V to 9V?
To reduce a 12V circuit to 9V, place two resistors in series within the circuit. Find the difference between the two voltages (12V – 9V = 3V) to determine the total amount of resistance needed.
What is pull-up resistor?
Pull-up resistors are fixed value resistors used between the connection of a voltage supply and a particular pin in a digital logic circuit. More commonly paired with switches, its purpose is to ensure the voltage between Ground and Vcc is actively controlled when the switch is open.
How do I choose a pull-up resistor for I2C?
These pull-ups would draw 3.3V / 1.77 k = 1.86 mA each when SCL / SDA is low. So, theoretically, if this bus has the absolute maximum amount of capacitance on it, this bus should use at least 1.77 k Ohm pull-up resistors, down to 171 Ohm resistors if their maximum low drive strength is 13.5 mA each during SCL/SDA low.
What is a strong pull-up?
A resistor with low resistance (relative to the circuit it’s in) is often called a “strong” pull-up or pull-down; when the circuit is open, it will pull the output high or low very quickly (just as the voltage changes in an RC circuit), but will draw more current.