What is the principle of operation of a pull-up resistor?

M

muhasa2017-02-08 21:36:51

Arduino

muhasa, 2017-02-08 21:36:51

Hello.
I'm studying the world of electronics, trying to understand how a pull-up resistor works. I roughly understood the essence - at the logical inputs / outputs you need to have strictly 0 or 1. So that the output does not give out nonsense under the influence of noise, you must either remove the electricity by setting it to logical 0, or set it to logical 1 by applying voltage. But I don't understand how it works in detail.
Let's take the connection diagram of the dht22 sensor to arduino uno ( www.picshare.ru/view/7902402/)
In this circuit, the first leg of the sensor is powered by 5V, the last leg is ground, the third leg from the left is not involved, and the second leg is, in fact, data. So, we immediately supply a voltage of 5 volts through a resistor on this date. It turns out that the leg, in order for a signal not 5V, but some other, to be considered from it, must somehow lower the voltage so that the arduino can read the values from the sensor? Or how does this scheme work, can you explain step by step? ..

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3 answer(s)

A

Armenian Radio, 2017-02-08
@gbg

easyelectronics.ru/osnovy-na-palcax-chast-4.html
easyelectronics.ru/avr-uchebnyj-kurs-ustrojstvo-i-...

S

Stalker_RED, 2017-02-08
@Stalker_RED

There will not be 5 volts there, there is a voltage drop on it.
Wiki: pull-up resistor
On the fingers: easyelectronics.ru/osnovy-na-palcax-chast-2.html

E

evgeniy_lm, 2017-02-09
@evgeniy_lm

Everything works according to Ohm's law
. If it's simple, then the output is a transistor with an emitter to the ground. In the closed state, the resistance of the collector-emitter junction is much higher than the pull-up resistor and all the voltage drops across the transistor i.e. on the collector (output) about 5V (1). When it is necessary to transmit data, the transistor opens, all the voltage drops across the pull-up resistor, at the 0V collector (output 0).
The Arduino uses AVR MKs, they have an internal pull-up resistor of about 50kΩ. Apparently, DHT sensors do not have their own pull-up resistor, and the internal resistance in the MK is high for them, so an additional 5-10k pull-up resistor is needed