VFD clock

Vacuum Fluorescent Display (vfd) is a vacuum fluorescent display. Its unique luminous effect is favored by many enthusiasts.

I have personally come into contact with several VFD screens, and most of them light up.

VFD display principle

Generally, the filament on the upper side of the screen is powered to excite electrons, and then there is a grid and anode on the lower side (analogous to the common end and segment end of a digital tube). Properly setting the potential of the grid anode and filament allows the electrons to bombard the phosphor on the anode. And emits wonderful light. The ones I came across include red, white, blue, green, yellow, etc.

VFD driver

That is, the serial-to-parallel conversion chip. The packaged VFD screens on the market have built-in drivers and code-breaking screens without drivers. Screens without drivers can use transistors or integrated serial-to-parallel conversion chips depending on the number of broken codes.

VFD power supply

Divided into filament power supply and high voltage power supply. The filament generally uses AC, because most screens are AC screens. If DC power supply is used, the different potentials on both sides will lead to inconsistent brightness and affect the experience. The high-voltage drive chip mostly uses negative voltage to bias the negative voltage to the AC filament. Then when the anode grid is given 0 potential, due to the low filament potential, electrons are attracted by the anode grid, accelerate and hit the phosphor to emit light.

• Some time ago, I happened to find a relatively large screen with the factory number HNM-18LM05T. Since the previous power supply solutions were all transformer oscillation solutions, this time I wanted to try the LM9022 dedicated chip. For negative high voltage, the AC voltage doubler rectifier output by the LM9022 is not used, and the lt1617 negative voltage boosting chip is used.
• Then there is the clock function. I first checked the relevant implementation, copied its function, and then innovated based on the feedback.
• Current demonstration video: https://www.bilibili.com/video/av56926233
• The program is currently hosted on github: https://github.com/sawyouintheheaven/vfd-clock  Please star if you like it