HackSpace – September 2019

TUTORIAL

Graphical output for (almost) any board

ometimes you need a little bit of

graphics or text output for your

projects and, for this, TFTs are a great

solution – they’re cheap, available in a

range of sizes, and well supported by

maker hardware. TFT stands for

thin-film transistor – essentially, TFTs are liquid crystal

display (LCD) screens with fast refresh rates. The

main thing you need to know when looking to get one

is the driver chip it uses. There are a few that are easy

to use; in this tutorial, we’ll look at ones driven by the

ILI9341 chip. The driver should come on the TFT

board, so we don’t need to worry about wiring the

two together. Instead, we just need to connect the

module to our microcontroller.

This connection uses SPI (plus a couple of other

wires), so the first thing we need to do is to connect

the four SPI pins to an SPI bus – it’s quite high speed,

so it’s best to make sure it’s on a hardware SPI. Most

microcontrollers have one of these, so look up where

yours are. The following connections go from the

relevant pins on the microcontroller to the labelled pin

on the TFT screen. We did this on an Adafruit Grand

Central, so the numbered pins are the ones we used.

S

• MISO (Grand Central pin 50)


• MOSI (Grand Central pin 51)


• CLK (OR SCK) (Grand Central pin 52)


• CS (or SS) (Grand Central pin 53)

The following aren’t SPI pins, but also need to be

connected. As they’re not part of SPI, it doesn’t

matter which pins you connect them to, provided

they’re digital IO. The pin numbers we’ve used

could easily be changed.

• DC (Grand Central pin 49)


• RST (Grand Central pin 48)

That’s all there is in terms of physical setup.

Let’s now take a look at what code we need. The

Grand Central can use either Arduino or CircuitPython,

so let’s take a look at how to use it in both these

languages. First, we’ll look at Arduino.

You’ll need to install the Adafruit GFX library –

that’s a high-level graphics library that can work

with a range of displays. You’ll also need the

low-level Adafruit-ILI9341 library that handles this

specific driver chip.

Graphical output

for (almost) any board

Add an ILI9341-powered screen in Arduino and CircuitPython

Above

Your TFT board

should have the pins

labelled to make it

easy to connect up to

your microcontroller

Ben Everard

@ben_everard

Ben loves cutting stuff,

any stuff. There’s no

longer a shelf to store

these tools on (it’s now

two shelves), and the

door’s in danger.