7-Segment Displays Wiring
Segment Indicators, Tech Guide

Numeric 7-segment LED indicators

The numeric indicators used in real airplanes can be replicated in your home cockpit using 7-segment LED modules, which can be a pretty realistic substitute, especially if you can find indicators with the right size and color.


The term "7-segment" is related to the form of displaying numeric information, and does not define the type of the display itself, its construction and operation. There are many display types (LED, LCD, Gas, Incandescent, etc.) that use 7 segments to display numbers, as well as 9, 14 and 16 segments for alphanumeric symbols.

Using 7-segment LED indicators in home cockpit is an easy way to simulate various devices displaying decimal numbers. In real planes some displays are made using such LED indicators.

However, most real equipment (especially older ones) may rather have Gas Discharge displays (as in most of Bendix King equipment), Fluorescent display modules, Incandescent indicators, and even electro-mechanically controlled numeric displays.

Since all these types of displays (except the mechanical ones) form digits using a 7-segment matrix, some of them can be reproduced using LED indicators of suitable size and color.

LCD displays

In newer equipment all these indicators are often replaced with LCD displays that have fixed 7-segment sectors or with LCD matrix displays.

Supported 7-segment controllers

SimVimCockpit firmware directly controls the following display types:

  • LED display driver MAX7219 - pre-assembled 8-digit modules or custom-made displays
  • LED display driver TM1637 - pre-assembled 6-digit and 4-digit modules
  • 16-bit LED drivers (DM13A and similar, see details below)
  • 8-bit shift registers (74HC595 and similar registers)
  • SimVimCockpit© firmware program code has been developed from scratch according to tech specification of every device type, without using any libraries.

    Each connected display can consist of up to 8 digits and be used to output 2 or 3 parameters simultaneously, when one parameter value's position is shifted relative to the other.

Pre-assembled and DIY custom displays

There are various pre-assembled modules on the market, with MAX7219 or TM1637 drivers, or modules with 74HC595 registers.

Usually, the MAX7219 module has 8-digits (sometimes 6) and TM1637 has 6 or 4 digits that allow you to quickly make any needed indicator for your panel - you just need to connect the display module as described and configure what to display on it and how.

If the sizes of the indicator digits are not suitable for making a display or you do not want to reduce digits number here are a few options:

1. Using MAX7219 with detachable display

First, you can simply desolder the 7-segment indicators from the MAX7219 module and use other indicators. This needs some skills.

But you can try to find max7219 modules with detachable indicators on the market. Then use any other 7-segment LEDs of the size and color you want. Here is an exaples of such module:

Another alternative is buying a MAX7219 LED matrix board with detachable LED matrix and use it.

The module has row and column connectors that are very convenient to use with 7-segment modules. Remove the LED matrix module and use any suitable 7-segment indicators instead (up to 8-digits).

You can buy one of the MAX7219 dot matrix modules here (example link, just $1 for piece).

MAX7219 "barebone" driver chip

If you are qualified enought in electronics, you can buy a driver chip and assemble your display accordingly with the MAX7219 driver specification, using appropriate 7-segment indicators.

The same you can do using DM13A drivers or 74HC595 registers as described below.

2. DM13A driver wiring

One of the easiest ways to drive 7-segment indicators is using the same LED driver ICs as for extended digital output in SimVimCockpit.

Trying this takes only a few minutes of your time, all you need is to take one DM13A driver or another similar IC and two 7-segment indicators. Also one constant or variable resistor 2 .. 10 kΩ is needed to set the desired brightness. Note: the indicators should have a common anode.

Thus, with a single driver, you can quickly assemble a 2-digit display, for example, for a voltage indicator. Adding more drivers to the chain, as shown in the diagram, you will get a display with any number of digits, from 2 to 8 for use with SimVimCockpit. Each IC in the chain drives 2 digits, and the last one - either one or two, depending on your needs.

Once the display module is assembled, connect the "S" input to the extended output assigned for this 7-segment display and two other signal inputs - "D" and "L" - to the common "D" and "L" output bus lines, as described on the "Connection" page.

Note: You can power the driver chip from the same +5V bus as your Arduino, but you should use appropriate power supply for the 7-segment indicators (+VLED). It can be a separate power supply or the same +5V source if it is powerful enough for all devices in your system.

3. 74HC595 Shift Registers wiring

Another option is to use the 74HC595 shift registers, which was implemented in ArdSimX. The difference from LED drivers is that one HC595 chip can drive one 7-segment indicator and it needs 8 resistors for each segment to be connected. The indicators should have a common cathode.

Note: You can use 7-segment indicators with common anode as well, connect the common anode terminal to +Vled power supply.

So, with a single chip, you can assemble a 1-digit display. Adding more registers to the chain, you will get a display with any number of digits. When joining several registers, you should connect together all "L" and "S" signals, as shown in the diagram below.

You can wire registers directly to the indicators or make a printed board. Another option is buying breakout boards with 74HC595 registers. You can find sample links on the "Components" page. All you need is to solder LED indicators with resistors to the board outputs.

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