Why do I need a pull down resistor?
The pull-down resistor must have a larger resistance than the impedance of the logic circuit, or else it might be able to pull the voltage down by too much and the input voltage at the pin would remain at a constant logical low value – regardless of the switch position. The appropriate value for the pull-up resistor is limited by two factors.
What kind of resistor do I need to run 12 volts led?
So to run a small LED off of 12 volts we need to use a 500 Ohm 1/2 Watt resistor. Enter any Starting Voltage, and then the Needed Voltage and finally the Current Draw (in AMPS) in the fields above then press CALCULATE to find other values.
What happens when you drop a resistor to 2 volts?
We need to find out 2 things, one the Resistance value needed to drop 12 Volts to 2 Volts and the second part of the problem is the wattage rating of the resistor. What is the Wattage Rating? Well when we drop the 12 Volts to 2 Volts we need to get rid of 10 Volts, where does that Voltage go?
What should the resistive value of a pull up resistor be?
Reducing the resistive value further, will produce a smaller voltage drop but increase the current. Then we can see that while there may be a maximum allowable resistive value, the resistance value for pull-up resistors is not usually that critical with resistance values ranging from between 10k to 100k ohms acceptable.
Why are pull up resistors used in microcontrollers?
It is neither in a high or low logic state, and a microcontroller might unpredictably interpret the input value as either a logical high or logical low. Pull-up resistors are used to solve the dilemma for the microcontroller by pulling the value to a logical high state, as seen in the figure.
How are pull up resistors used in a logic circuit?
Pull-up resistors are resistors used in logic circuits to ensure a well-defined logical level at a pin under all conditions. As a reminder, digital logic circuits have three logic states: high, low and floating (or high impedance).
How is a pull up resistor connected to a Vcc supply?
This condition means that their output is either grounded when LOW, or floating when HIGH, so an external pull-up resistor, (Rp) needs to be connected from the open-collector terminal of the pull-down transistor to the Vcc supply.