pull-up resistor
I am confused about the concept of a pull-UP resistor.
With resistance, voltage will always be decreased???? right?
Can someone please point me to a resource that explains this? thanks.
I am on p 79 of What's a Microcontroller (Fig 3-9), and I just cannot understand this concept.
A little confusing also is that when using the pullDOWN resistor it pulls voltage to -0-. There should still be some voltage....is it more like "not enough to matter"?
I tried eliminating the pull UP resistor....when the button is pushed the stamp resets. Maybe this means that the voltage was low, causing the reset. So it really needed a pullUP resistor apparently.
I have just discovered the stamps. Great fun! I have wanted to learn something about electronics for years, so this is an excellent way. At one time I programmed a lot in BASIC so the programming part is easy.
Best regards
Mark
With resistance, voltage will always be decreased???? right?
Can someone please point me to a resource that explains this? thanks.
I am on p 79 of What's a Microcontroller (Fig 3-9), and I just cannot understand this concept.
A little confusing also is that when using the pullDOWN resistor it pulls voltage to -0-. There should still be some voltage....is it more like "not enough to matter"?
I tried eliminating the pull UP resistor....when the button is pushed the stamp resets. Maybe this means that the voltage was low, causing the reset. So it really needed a pullUP resistor apparently.
I have just discovered the stamps. Great fun! I have wanted to learn something about electronics for years, so this is an excellent way. At one time I programmed a lot in BASIC so the programming part is easy.
Best regards
Mark
Comments
A pullup resistor provides a known voltage to an I/O pin. Since the input circuit draws very little current (microAmps), the resistor can be high in value (10K to 100K typically) and connects the I/O pin to the supply voltage of the chip (+5V in this case). When the switch is actually closed, the high value limits the current through the switch and the switch can very easily bring the voltage of the I/O pin very very close to ground.
You can reverse the roles of the switch and pullup to make a switch and pulldown resistor with the switch connecting the I/O pin to the supply voltage and the resistor providing a known zero voltage to the I/O pin when the switch is open. It's often easier to connect the switch to ground, so most circuits of this sort use a pullup resistor.
I sure am glad I discovered these products. They are great!
Thanks to you and other great educators on here too.
m