4/2/2023 0 Comments Vfd displays![]() The whole multiplex process and the high-voltage drivers are usually provided by dedicated controller/drivers such as the Princeton PT6312. The cathode/filament is heated by a small AC voltage (about 3V) that is superpositioned on -20V DC. The solution is a negative voltage of about -20V for the cathode and -25V for the de-activated Grids and segments. When the cathode reference was to be at GND this would is not be sufficient to illuminate the segments. Typically the most positive voltage is Vcc (5V). The powersupply for VFDs is a bit elaborate. You may be able to see a red glow when you observe the filament wires in a darkened room. Note that the filament is mounted on metal springs to make sure the wires remain under tension when expanding or contracting due to heating. The picture below shows the filament/cathode, the grids and the segments. So the grids are activated one by one to multiplex all digits sequentially. When the grid is negative wrt to the cathode the electrons are all pushed back and all segments remain dark even when they have a positive voltage. When the grid is positive wrt to the cathode the electrons will pass and just fly through the grid maze towards the segments. The grid looks similar to a ''chicken fence''. The intensity depends on the voltage and the dutycycle.Įach digit has a separate Grid in front of it. The colour depends on the type of material (typically blue/green, orange). When the segment has a positive voltage wrt to the cathode the emitted electrons will hit the phosphor and emit light. The segments are formed by specific conductive shapes with a deposited layer of phosphorus material. The device has a filament of parallel wires that is heated and emits electrons. The contact wires are melted into the glass body. A VFD consists of a glass tube or glass box that is vacuum and airtight. The VFD operation is similar to a vacuum tube or CRT. The operating principle remains the same. ![]() ![]() The 14- or 16- segment 'starburst' displays are more suitable than the 7 segment versions when you need more flexibility to display characters or symbols. VFD controllers such as the Princeton PT6312 have internal memory for all segments and will activate each digit sequentially at a high update rate (> 75 Hz) and the result is that all digits seem to be on continuously. This multiplexed approach reduces the number of pins. In some cases the displays also feature additional segments for the decimal point (dp), colons or symbols. The same segments of all digits are usually connected together and provided as external pins and each digit is enabled or disabled by a Grid pin. The seven segments are usually identified by the characters a-g. These types can all display numbers 0-9 and some characters like A-F. The best known types are the seven segment displays (e.g. However, they look good since they have nice bright colors and are readable in daylight. They are not cheap, unless produced in large numbers. You will find them in audio and video equipment (eg DVD players), Point-Of-Sale stations, car displays etc. Vacuum Fluorescent Displays (VFD) have been around for quite some time, but they are still popular.
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