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How do you calculate pull down resistance?
To calculate the pull-down resistor value, it’s slightly different from the pull-up resistor value. Knowing that current is 100uA, we’ll take 0.5v as our pull-down voltage since the input is 0.8v. Thus, applying our R = V/I once again, but this time we don’t have to minus, so our formula remains constant.
Why does a phototransistor need a pull-up resistor?
1 Answer. The pull down to ground is used to create a voltage divider, with the top half being the relative resistance of the Photo transistor. Without the pull down, you only have a series resistor, which results in very little if any voltage drop across it in a low impedance input setup.
What do you need to know about pull up resistors?
The short and easy answer is that you want a resistor value on the order of 10kΩ for the pull-up. A low resistor value is called a strong pull-up (more current flows), a high resistor value is called a weak pull-up (less current flows). The value of the pull-up resistor needs to be chosen to satisfy two conditions:
How to calculate pull up resistors for I2C?
You can use this tool to calculate the minimum and maximum allowed values of the pull up resistors required for your I 2 C bus, based on the desired operation mode ( source ). It is based on the official I 2 C bus specifications and is taking under consideration the constraints set for each mode.
Are there pull up resistors in ultra fast mode?
Ultra Fast mode devices offer push-pull drivers, eliminating the pull-up resistors. The calculator uses the following electrical specifications for each I 2 C mode:
How does the pull up resistor work on a VCC?
When the button is pressed, the input pin is pulled low. The value of resistor R1 controls how much current you want to flow from VCC, through the button, and then to ground. When the button is not pressed, the input pin is pulled high. The value of the pull-up resistor controls the voltage on the input pin.