This project can turn your GU7000 series VF display (manufactured by Noritake Itron) into the grayscale-able display. In this case I use GU280x16G-7000. I use ESP-01S and communicate with the display through Async(rs232) but it's 5 volt bus. The principle of this method is in the first picture of the project page.
GU7000 VFD display capable of 8 brightness levels and we can change brightness anytime without to re-init the display. The GU7000 series have feature to display static monochrome image. but what happen if we can display multiple bitmaps and every bitmap has it own brightness levels. we can combile multiple bitmaps with multiple brightness levels then our eyes will pick up as static image. This phenomenon call "POV" stand for Persistence Of Vision. It's like tricking our eyes. the flow-chart in the image of the project is the workflow of FakeGrayscale in void loop.