TFT Conversions - Read First

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Published: Sunday, 01 December 2024

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DISCLAIMER: This is educational only, so if you decide to do the same yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this and try it yourself.

I have converted various test instruments to TFT LCD using the same design philosophy throughout.

At the heart of each conversion is the inexpensive STM32 "Blue Pill" development board, acting as a bridge between the instrument and a modern TFT LCD.
The firmware monitors the instrument's original display interface, decodes the incoming data stream, and reproduces the display on a high-resolution colour TFT.

By using the same hardware and software architecture across multiple instruments, new conversions can be developed quickly while maintaining a consistent design and user experience.

Rather than driving the LCD directly, the Blue Pill communicates with an LT7680 graphics controller over a high-speed SPI interface.
The LT7680A-R IC is a powerful embedded graphics controller with its own display memory, font engine and graphics acceleration, capable of driving high-resolution TFT LCD panels.

By offloading all display generation to the LT7680A-R, the STM32 only needs to send text and graphics commands, leaving the graphics controller to render characters, lines, shapes and images efficiently.

This approach provides smooth display updates, crisp text and a consistent platform that can be reused across many different instrument conversions.

To bring this all together I have designed a PCB that fits the individual instrument and that incorporates a minimal amount of parts to hold the BluePill & LT7680 Pcb, and also to provide the IO connections.

The TFT panels themselves are bright, high-contrast IPS displays with excellent viewing angles, offering a significant improvement over the ageing LCDs, VFDs and CRTs found in many vintage instruments, while remaining readily available and inexpensive.
Over the instruments I have converted thus far I have only used two different models of TFT LCD:
https://www.buydisplay.com/bar-type-3-71-inch-240x960-ips-tft-lcd-display-spi-rgb-interface
https://www.buydisplay.com/bar-type-4-58-inch-320x960-ips-tft-lcd-display-spi-rgb-interface

I have a dedicated webpage for each conversion and associated YouTube video. In there you'll also find the Bill of Materials, Instructions, Pcb gerbers and any other info so you can upgrade your own instrument.
There is also an dedicated Github resource for all my source code including the compiled HEX files for each instrument:
https://github.com/Ian-Johnston?tab=repositories
The individual HEX files are located in the following project sub-folders:  /VisualGDB/Debug/
I.E. 34401A_VS_Display.hex

The Development Environment

Visual Studio 2022 together with the VisualGDB plugin provides a professional development environment for the firmware.
VisualGDB integrates seamlessly into Visual Studio, allowing embedded STM32 projects to be edited, compiled and debugged without leaving the familiar Visual Studio interface.

It provides full project management, code completion, syntax highlighting, integrated build tools, source-level debugging, and direct programming of the target hardware via an ST-LINK debugger.

The ability to set breakpoints, inspect variables and registers, view memory, and single-step through the firmware greatly simplifies the development and debugging of complex real-time embedded applications.

By combining Microsoft's powerful IDE with the GNU ARM toolchain and STM32 development tools, VisualGDB offers a productive and stable environment for developing, testing and maintaining the TFT conversion firmware.

Source-level debugging is done through the BluePill's SWD connector, the USB connector on the BluePill is not used.

You don't need the development environment unless you want to make changes to the code. For the end user all you need is the compiled HEX file which I supply, and then follow the easy programming procedure below.

My current toolchain:
Visual Studio 2022 Community Edition = free
VisualGDB Custom Edition V6.0R8 = $189 (lifetime) - Note: The cheaper Embedded version at $99 would suffice I think
STLinkv3set debugger/programmer = £38

Note: Screenshot opposite of VS2022, light mode enabled (I usually run it in dark mode).

Programming the BluePill Board

Use an STLink V2 or STLink V3 programmer. Clone programmers should also work. Leave the Boot0 & Boot1 headers in their default positions. The following can be carried out with the BluePill installed in the meter and my PCB connected. If programming the BluePill standalone, you will need to supply the board with +5V.
The 3.3V connection is not used for powering the BluePill, it is an input to STLink and is used for programming voltage detection.

Supported Instrument Conversions

Here's what I have done so far, and the possible future projects coming up next!
I don't just pick instruments at random, I really have to own one myself and also the protocol and hardware/software display interface has to be known or is somewhat reverse engineerable!

Are these free?

Yes, all my conversions are basically open-source & free. I publish all the source code, gerbers and everything else you need to convert your own test instruments just like mine.
Download it all, order your parts and you can end up with a great looking test instrument once again! Many people have.
How about donating?............YES!, you can PayPal me via this link here.
I have put hundreds of hours into these conversions so every penny is much appreciated.

DISCLAIMER: This is educational only, so if you decide to do the same yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this and try it yourself.