Arduino Interface Hardware: Find out exactly how to interface Arduino Microcontrollers to inputs and outputs. Included here are some unusual techniques like Charlieplexing.

Arduino Interface Hardware:

This page provides a collection of useful interfacing techniques including:

• Button Input Debouncing (get a single output for a single press!).
  
  
• Charliplexing (Save pins when driving LEDs).
  
  
• Rotary Encoder Debouncing (more difficult).
  
  
• Serial Interface Protocols.

Arduino Interface Hardware

Switch Debounce

You may be surprised when you first accept input from a push button, that it does not just generate a clean output but actually generates a lot of on/off signals in a very short space of time.

If you are not careful, a single button press can result in your code counting up 10's of button presses. This is obviously not useful if you want to increment a variable by one!

You have to get the switch under control and the link below shows you some easy ways to do it.

Arduino Toggle Switch

You don't need to buy a toggle switch as it is possible to make one using only a push button and a microcontroller. A physical toggle remains in which ever state you leave it i.e. it has memory! 

Making a toggle switch from a push button just requires the Arduino to remember the current state of the switch.

Arduino Joystick

A Joystick is one of those thumb controllers on a game pad. they provide x-y positions of the joystick by moving two potentiometers - one for each axis.

This tutorial showing you exactly how to read the outputs of the potentiometers but makes it simpler by using a new library.

Charlieplexing: Arduino Interface Hardware

Or how to save I/O pins when driving LEDs!

Charlieplexing uses a clever trick:

    The fact that a reverse biased LED is a diode that stops current flow.

Combined with the ability of microcontrollers to change an input to an output on the fly the circuit current flow can easily be altered to light specific LEDs, but more importantly you can control more LEDs than there are controlling pins!

This clever trick uses the fact that a reverse biased LED is a diode that stops current flow

Logic Level Converter

One problem you will come up against is the fact that your system uses 5 volts and the chip you want to use must only have 3V3 (including the control signals). Its ok if the signals are all going to the 3V3 chip as you can then use voltage dividers.

The problem comes if you need to change direction with the same signal. Fortunately, there is a very elegant solution using two resistors and a MOSFET!

Rotary Encoder: Arduino Interface Hardware

It's not the first thing that comes to mind when using a rotary encoder:

    They just don't work right - producing all kinds of spurious signals.

Even though they use Grey encoding (that ensures only on signal changes from one movement to the next) they are still an absolute pain. It's all due to switch bouncing inside the device as the metal contacts bounce on and off the substrate when you rotate the shaft.

There are several solutions such as capacitor smoothing but if you don't want to slow things down too much a more elegant solution is to use a state machine. In the code below you can get your rotary encoder to reliably output single digit changes with absolutely no skipping.

I2C Serial Interface Protocol

The I2C protocol saves you a lot of wiring as it is a 2 wire interface. Not only that, it is also a multi-drop - multi master system with bi-directional communication (Remember that logic level converter?).

The I2C protocol allows communication in both directions between the master controller and slave devices so you can have very complex systems e.g. gathering data from an ADC and sending data to a display; all on same two wires.

SPI Serial Interface Protocol

The SPI interface is a much simpler interface than I2C, but because it is simpler it can operate far faster e.g. a typical I2C rate is 400kHz but SPI is 10MHz. Updates to I2C let it go at ~3MHz but never as fast as SPI.

Lots of chips implement SPI for this reason; Sometimes you have to get a faster data throughput at the expense of a "fancy" protocol.

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