Weekly Devlog #2

This week i started prototyping the design decisions i had made with the PCB to ensure before manufacturing it works. So i wanted to simulate most of the important factors like the 74HC138 circuit i would use to control the 6 TFT display boards, while also checking whether 3.3v would properly power the board, in addition i plan to run tests to see in the current design how much power pull will be pulled from the computer to power the hackpad. Included in this is also instructions on how to build the full protoboard which can very easily be expanded to include up to 8 TFT displays. This prototype version doesnt include switches which will be next weeks addition including building the foundational code for the entire board.

Instructions

To begin i first put in each component of the board:

• 2x TFT 1.28 inch Display
• 1x 74HC138N circuit
• 1x Arduino Uno R3

Each component besides the Arduino can be found in the first accompanying image with the round board being the TFT display and the rectangle box being the 74HC138N circuit, not shown is the Arudino Uno i believe any mainstream microcontroller can be used for this, just follow the pins.

Power Management

From there its best to start on power management utilizing the rails on the breadboard i connect the Arduino Unos 3v3 pin and any gnd pin to the respective holes on the board. In total i use 5 positive wires and 6 negative wires. The TFT boards power management setup is straight forward follow the writing on the board, however the more difficult section is the 74HC138 which in total needs 4 separate power wires.

To start wiring it find the tiny hole on the actual circuit itself its a little divot in the box, 3 pins down from the top pin on the side of the divot is E0, which the next two pins below it is E1 and E2. These control the setting of the controller, to achieve the setting we want we need to wire E0 as low or GND E1 as low and E2 as high or 3V3, from E2 skip the next pin going down from E2 and the final pin on the left side of the controller is the GND pin. Finally the last pin needed is the pin to the right of the little divot mentioned earlier this is the VCC.

TFT Logic

The next step is where the wiring gets almost unbearable (jumper cables am i right), this is the logic section where the tft boards pins will all be filled up. To start in a section of the breadboard where the is no other connections to the column of holes we need to create our own bus. We need 4:

• RST
• DC
• SDA (SCK)
• SCL (MOSI)

To create the bus just connect 3 wires in the same column these wires will now share the same electrons. from there simply connect the the first wire of the column doesnt matter which direction it just is best to make sure its the first one in that column. The pin for the arduino is as follows:

• RST - Reset
• DC - 9
• SDA - 11
• SCL - 13

Make sure to connect the wires in that bus to the pin of the tft board it corresponds to

74HC138 Logic

The final step is the logic for the 74HC138 circuit which requires 3 digital pins which handle the selection of the outgoing pin to the CS. To start the 2nd pin on the left of the divet in the circuit is A0 the next 2 pins are A1 and A2 each of these pins need to be given a digital pin i wired it to pin 7, 6 and 5 i believe any pin would do. Lastly the 6 pins below the VCC and the pin above GND are the actual output pins these can be wired to the cs of the tft displays to allow information to flow and commands. Simply wire Y0 and Y1 which are the first two pins below the VCC to one displays CS and the other to another CS.

Conclusion

Now you have a working multi display breadboard, in my GitHub i will link the code for the prototype board. In addition each section has picture linked which are shown in order of the instructions sections, if my instructions suck simply look at the photos and hopefully it will clear any confusion