LED 7-Segment 0.56″ Red CA

Common anode red LED display with decimal point

DESCRIPTION

These 7-Segment common anode red LED displays include a decimal point and have a character height of 0.56″

PACKAGE INCLUDES:

• LED 7-Segment 0.56″ Red CA

KEY FEATURES OF LED 7-SEGMENT 0.56″ RED CA:

• 7-Segment with common anode (CA)
• 0.56″ high characters
• 20 mA current
• 2V forward voltage drop
• Red color

7-Segment displays are very useful for making numeric or hexadecimal displays such as for a clock, timer, counter, voltmeter or similar application.

Theory of Operation

These displays have 7 separate LEDs comprising the 7 segments of the display plus an 8th LED that functions as a decimal point.  The LEDs are labeled segment A thru G and the decimal point is DP.

The displays are common anode (CA) type which means that all 8 of the LEDs have their anodes tied together (in common) and these connect to the center pin on each end of the display which are then connected to Vcc.

To light a particular segment, the control (cathode) pin for that segment is driven LOW.  These 8 control pins should each have series current limiting resistors to prevent damage to the LED module or the uC.  Instead of the control pins, current limiting resistors can be put on the pins connected to Vcc so that fewer are needed, but in that case the brightness of the display will vary depending on how many segments are lit at one time so that practice is not really recommended.

The pin-out shown here is as if you are looking at the face of the display.

These displays are logic compatible with a max drive current of 20mA and a forward voltage drop of about 2V.

Calculating LED Resistor Values

At an operating voltage of 5V, a series current limiting resistor of 150 ohm will provide max brightness or larger resistors of around 220- 330 ohm can be used to reduce current at a slightly lower brightness.  These are fairly bright displays so under-driving them a bit usually makes for a nicer looking display unless they will be used outside where max brightness is desired.

If you are using multiple display modules in a multiplexed mode where each display is only lit for a portion of the time, the maximum allowable current can be greater than 20mA and can go up to as high as 70 mA.  In that case, you generally want to drive the display with more current since the display is on only a portion of the time and will therefore appear dimmer than if the display was being driven constantly on.

OUR EVALUATION RESULTS:

These are good quality modules.  Having the pins on the ends of the module make them more breadboard friendly that modules that have the pins on the sides.

We like 7-Segment LED displays because they display numbers in a very clear format and they are available in everything from small 0.3″ to very large 5″ or larger up to 12″ tall characters.  Being encapsulated, they tend to be fairly rugged devices and they have good brightness that is visible even in sunlight. If you are building an outdoor race timer or something like that, they tend to be the go-to display to use.

The downside to 7-Segment LEDs is that they require 7 or 8 drive pins per display module.  If there are multiple modules, the number of required output pins on a microcontroller increases quickly.  Fortunately, there are ICs like the MAX7219 that are made to interface with these modules.  Communication to the uC is made over the I2C bus and the chip takes care of updating and multiplexing up to 8 of the 7-Segment modules using only 3 pins on the microcontroller.

Notes: 

1. None

TECHNICAL SPECIFICATIONS