Its also good practice to include a "protection" resistor, Rprot as if the button is inadvertently wired to the wrong supply rail an excessive current can flow into the pin, damaging the circuit. We need a "pull-down" resistor Rpd to ensure Pin D4 is at a logic zero when the button is released. Pin D3 will be at a logic "1" when the PB3 button is pressed - but when its released the value will be indeterminate because the input is floating. Here we see a button connected to the Vcc rail. The circuit around PB2 / Pin D2 shows a correct implementation before the button is pressed, and after it is released, Rpu the external pull-up resistor will ensure it is at the correct voltage to generate a good logic 1. HOWEVER if you configure the input as "INPUT_PULLUP" the Arduino connects an internal pull up resistor - so it behaves like the nest circuit (PB2/D2) Most likely it will NOT immediately go to a logic 1 when released. PB1 will generate a good logic 0 when pressed but when its open Pin D1 will be floating and give unpredictable results. This has many advantages - but the "active" (pressed) condition of the button results in a logic "0" and inactive or released condition gives a "1".įIG 1 Here we see good and bad implementations of a push button connected between a digital pin and the ground rail. The usual (MUCH better) choice is to use a ground connected "normally open" button or switch. Now lets look at how we can provide logic input signals to the Arduino.īuttons, switches, pull up (and pull down) In using a switch or push button to provide a digital input to the Arduino we basically have two options as shown here to connect one side of the switch or button to the ground 0V rail. Most Arduinos use the 328 or 32U4 chips the later Due, Zero and others use more powerful processors that run from 3.3V however the electrical characteristics are similar. In the following information, unless otherwise stated all data and values are taken from the data sheet for the ATMega328P which powers the Arduino Nano. However a common factor is that for all ArduinosĪ pin that is not programmed behaves as a digital input, Pin 7: Digital Input or Digital Output Pin 4: Digital Input, Digital Output or Analog input Pin 5: Digital Input, Digital Output or Pulse Width Modulated outputĮach member of the Arduino family has differences so you will need to check the pin configuration for the Arduino you are using. Lets look at some examples on the Arduino Nano I'll refer to the pin numbers as shown on the board itself. To give maximum flexibility each external connection on and Arduino board may share different functions. ![]() Behaviour of digital pins configured as inputs.Digital input characteristic and hysteresis levels.Values for pull-up, pull down, and protection resistors.Buttons, switches, pull up (and pull down).This article looks at some alternative ways of connecting digital input devices - switches and buttons. Introduction All the Arduino family of microcontrollers have pins that may be used as inputs.
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