By Floris Wouterlood – The Netherlands – June 1, 2021 –
Many Arduino projects require adequate display of what is being monitored. Think of time, temperature, humidity, pressure, sound, light, voltages, or combinations of recorded data in a weather station. With the addition of fast and capable ESP32 microcontroller boards to my personal ‘fleet’ my collection of good old Arduino Unos with their TFT display shields seemed prone to gather dust. The ESP32 combines well with TFT displays through a 4-pin SPI interface* while the Uno shields have parallel interfaces that feature 28 pins of which a minimum of 13 is necessary for the daily display business (see figure 2). A parallel interface is generally faster than a SPI interface. The prospect of a bunch of shield displays with fast parallel interface parked forever in a deep drawer was a stimulus for me to start a project to connect these shields to an ESP32. Fortunately there are several solutions available of which I selected the one proposed by Alberto Iriberri Andrés at https://www.pangodream.es/ili9341-esp32-parallel. However, the nightmarish prospect of connecting shield after shield with an ESP with unwieldy Dupont jumper wires inspired me to create a Uno-shield compatible parallel ESP32 TFTdisplay workbench for the purpose of checking all my Uno TFT shields, one by one. Here follows the design, wiring, and the results with a collection of parallel Uno shield type displays.
Uno TFT display shields
The market is swamped with TFT shields that can be placed directly on the pin sockets of an Arduino Uno. These shields feature parallel interfaces. They have in common that there are four pin header blocks through which one can stick such a shield very handy right onto a Uno (fig. 2). The displays mounted on these shields have different pixel dimensions and, more important, different controller chips. Most commonly used are ILI9341, ILI9481 and ILI 9486 chips. The best performing TFT shields are equipped with 3V-5V voltage converters (e.g. the shield shown in fig 2) but there are plenty of cheap shields available that lack a voltage regulator and therefore accept only 3V.
Controllers need their own specific driver to make the display work correctly. A major effort to supply the Arduino world with adequate drivers for ESP8266 and ESP32 microprocessors running smoothly with the above ILI controllers has been undertaken in recent years by the electronics engineer known as Bodmer: the TFT_e_SPI.h library.
Considerations for a bench design
So what I needed is a board that accomodates an ESP32 and that has enough space to accommodate a variety of small (2.4 inch) and large (3.95 inch) Uno TFT shields.
The base board consists of a doule-sided soldering board fastened with four nylon spacers on a piece of cardboard. Mounted on this base are two 15-pin parallel socket headers to accommodate an ESP32 microcontroller board and the four socket headers to accommodate the Arduino Uno TFT shields to be tested. As screen diagonals of TFT shields in my ‘arsenal’ vary between 2.4 inch and 3.95 inch, a 12080 mm double-sided soldering board with 4230 holes was selected for this purpose. The positioning of the socket headers is shown in figure 3. There are also two 2-pin pin headers to allow to select the proper voltage to power the display being tested (with jumpers).
Electronic parts needed
12080 mm double-sided soldering board featuring 4230 holes, two 15-pin socket headers, two 6-pin socket headers, two 8-pin socket header, one 3-pin socket header, one black 2-pin socket header (black), two 2-pin headers (red), four nylon bolts, four nylon spacers and four nylon nuts, ESP32-WROOM32 microcontroller board with 30 pins, wire, two jumpers.
Solution for pin header block pitch unorthodoxy of Uno TFTshields
The positioning of pins on the original Arduino Uno does not follow the uniform 2.54 mm (0.1 inch) pitch rule. Any Uno parallel TFT shield therefore will not immediately fit a standard soldering board. On the back of each shield are jumper blocks labeled J1 through 4 (figure 2). We call J1 here the ‘SD jumper block’, J2 the ‘parallel jumper block’, J3 the ‘control jumper block’ and J4 the ‘power block’. Part of the SD jumper block is occupied by the parallel data interface. Some manoevering makes it clear trhat the J2-J3-J4 blocks fit the holes of the soldering board while the parallel jumper block (J1) is the outlier. Fortunately, the pins in all blocks follow the 2.54 mm pitch rule. It is J1 as a whole that is half a unit positioned ‘out of pitch’. Through this unorthodoxy, say asymmetry, a TFT shield fits an Arduino in only one way. Very clever. The present soldering board was adapted to this configuration by cutting a narrow sleeve where the pins of the J1 parallel jumper block should be, just wide enough to let the pins of the corresponding socket header through. Then an extra piece of soldering board was prepared and fastened with wire and solder under the sleeve, taking care that the J1 accepting socket header would exactly match jumper block J1.
The design is quite simple: two parallel rows of 15-pin socket headers serve as a mounting point for the ESP32 (figures 2,3). These sockets are positioned in the upper left corner of the board to leave as much area as possible to position the TFT shields. Here, TFT shields are oriented landscape. The bench is designed only for displaying data and graphs only, with no SD card reader support.
All Uno TFT shields have three pins that deal with power (3V3, 5V, GND), five pins that are necessary for display control and eight pins connected with the parallel data transfer interface, i.e., there is a total of 16 pins that need to be wired (figure 2). In addition I planned three ‘free’ pins of the ESP32 available via pin sockets for input-output puposes: pins D2, D5 and D15 (figure 4).
Pin wiring: four groups
With so many wires it is necessary to bring order in the assembly of the bench. One can distinguish (1) power wires, (2) TFT control wires, (3) parallel interface wires, (4) additional wiring. One by one the groups of wires were mounted on the soldering board.
These are shown schematically in figure 3.
These are shown schematically in figure 4.
TFT control wires
The group of control wires originates from pins D26, D27, D14, D12 and D13 and connect to the socket header that accomodates TFT shield jumper J1 (figure 5).
Parallel interface wires
There are eight data pins on the TFT shields, marked LCD_D0 through LCD_D07. LCD-00 and LCD_01 are pins on jumper block J3 while the remaining LCD_nn pins can be found on jumper block J2. These pins must be connected to, respectively, pins RX2, D4, D23, D22, D21, D19, D18 and TX2 (figure 6).
For the sake of completeness and oversight the pin connectivity is presented below as a Table.
Pin connectivity table
According to the scheme published by Alberto Iriberri Andrés at https://www.pangodream.es/ili9341-esp32-parallel