Archive:Cash Register Display

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Cash Register Display Release status: experimental [box doku]
Description	Display text in the space
Author(s)	tarwin,tiefpunkt

We have a VFD Display in a strong metal casing, which used to belong to a fast-food cash register.

Hardware

The display is a 2x20 VFD display, which is controled via a serial interface. Inside used to be an interface board.

Display Board

The display board takes 5V at ~0.6A. There's a 7 pin connector to connect to the interface board.

Pin	Function
1	5V
2	5V
3	Reset
4	Data (RX)
5
6	GND
7	GND

There used to be a 1.3A fuse on the board. That burned, and now needs replacement.

Interface Board

The interface board connected the display board to the outside world. It took some higher voltage to convert it to 5V, and RS-232 levels to TTL level understood by the display board.

It seems that the board does not work anymore. Tests showed that the voltage regulator outputs ~10V instead of 5V. So we dropped the board and connect directly to the display.

Electric Imp

Instead of connecting via the supplied RJ45 cable to the serial board, an Electric Imp was used to connect the display to the net. The display's RX is connected the Imp (UART12)

Software

Send text to mumalab/room/display on the MuMaBus and it'll appear on the display.

Inner workings

      |--------- MuMaBus ---------|                                |------ Inside Display Case -------|
 ---> (MQTT Broker) ---> (Node Red) ---> (Electric Imp Cloud) ---> (Electric Imp Device) ---> (Display)
 MQTT               MQTT            HTTP                       ???                       UART

The display takes serial input at 2400baud. Inside are jumpers to change speed, but we left it at that.

The Electric Imp inside exposes a web API (via ElectricImp's sucky cloud magic), and sends the input from there straight to the display's serial input.

The MuMaBus takes input on mumalab/room/display, does some replacements to match the displays character font, and sends it via the Imp's API to the display. This is the suggested way to access the display.