As I said in the previous post, the 2.8” touchscreen is too small. And its resistive touch isn’t responsive enough.

On the picture below the top left one is the “old” 2.8” resistive touch display.

So I had to test new capacitive touchscreens : 

• 2.8″ 320*240 pixels, ratio 4:3 (bottom left)
• 3.2″ 320*240 pixels, ratio 4:3 (the one in the middle, fitted into my MicroDexed Touch)
• 3.5″ 480*320 pixels, ratio 3:2 (right)

To give an idea of the pixels gained with the 3.5” resolution 480 * 320 compared to the 320 * 240 pixels : 

After a little poll between us, we decided to go bigger. So I bought a 4″ capacitive screen (480*320 pixels, ratio 3:2) to have more space. The code for this new type of display needed new libraries for the new drivers (ST7796 for display and FT6206 for touch) and some rewiring. Fortunately Paul had anticipated everything and exposed pins for both the microcontroller and the display on the PCB so it was an easy fix.

This time the display was too big to fit between the encoders, so I desoldered the left encoder…

Now we have a comfortable display, with responsive touch

To be continued…

David

When we started assembling our Zyklus clones, we realized how complex it would be to upgrade the hardware (based on a Z80) and the software written in assembly language.

Just take a look at the PCBs needed for the ReZyklus :

Especially since we couldn’t find the toolchain to compile the old assembly code for rewriting EPROMs. So, the idea quickly emerged of perhaps developing a V2 based on modern, simplified hardware and a software layer that was easy to write, compile, and maintain.

After much discussion and experience with other projects, we chose the Teensy 4.1 microcontroller.

At the end of 2024 I spoke about this V2 with Paul, our electronics wizard. Rather than embarking on “spaghetti” breadboard projects, I suggested building a prototype PCB to validate the hardware choices and confirm that we could indeed achieve our desired functionality. Paul recommended using the HT16K33 chip, which can scan up to 39 buttons in a single scan and control up to 128 LEDs. So the prototype PCB includes:

• a Teenzy 4.1 microcontroller
• a HT16K33 chip
• a 2.8″ resistive touchscreen
• three rows of eight buttons, each associated with an LED
• two rotary encoders
• two MIDI IN and two MIDI OUT ports
• a buzzer
• a footswitch jack input
• a jack input for an external clock
• a USB host port

I ordered the PCBs and here’s what it looks like :

After soldering the components and writing some code to test them, it immediately becomes much more enjoyable

Here I used the same “vintage” buttons as on the ReZyklus V1.

But then I realized that a 2.8″ touchscreen was really small, and the resistive touch wasn’t very responsive. So I looked for another solution.

To be continued…

David