Bistable display element
A bistable display element , also known as a flip-dot , is an electromagnetic- mechanical component that shows one of two differently colored sides of a small plate via a tilting or rotating device, depending on the control. Bistable display elements are mostly assembled to form matrix displays and are used in display panels and the like. a. in vehicles such as buses , railroad vehicles and subway , light rail or tram cars as well as in train stations and airports .
Structure and functionality
Usually a square plate (display plate), which is mounted diagonally rotatable, is located at the visible end of a bistable display element. The two sides of this plate are colored differently, with one side usually black, the other side usually in a strong contrasting color such as white, yellow, orange or light green. There is a permanent magnet in the core of the indicator plate . Behind the display plate there is an electromagnet which , depending on the polarity, exerts a force on the plastic plate and turns it around.
In order to prevent the indicator plate from pivoting back after the electromagnet has been switched off, there is usually a latching device which, in the simplest case, consists of a non-round axis of rotation. The remanence of the iron core of the coil is sometimes used to maintain the magnetic field over the long term. The indicator plate thus has two stable states, hence the designation bistable .
The advantage of this type of display is that energy is only required to turn the plates over. If the display stays the same, no energy has to be used. This means that bistable displays are advantageous in areas of application in which the display rarely changes.
While older matrix displays may have been illuminated from the side (example image of a local train) in order to remain legible in poor lighting conditions, newer bistable display elements have a built-in LED that illuminates the display plate if required .
Other designs
In the past, instead of the square display plate, there were mainly cylinders that are rotatable around their own axis.
Signal relays are used in control rooms, which display their switching status or save a change in status; see relay .
Display elements that are used in seven-segment displays such as those used at petrol stations have a different design, but the same functional principle .
Classic electronic e-paper displays are bistable and retain their image when the power supply is switched off.
Bistable LCD
Bistable LCDs are LC displays that keep their display without additional batteries or backup capacitors . With this type of display, energy is only required to change the alignment of the liquid crystals. Once positioned, these will keep their orientation until they are reoriented the next time they are adjusted.
