LED 7-Segment 0.56″ Red CC 3-Digit

Description

These 3-digit 7-Segment common cathode red LED displays include decimal points and have a character height of 0.56″.

PACKAGE INCLUDES:

• LED 7-Segment 0.56″ Red CC 3-Digit

KEY FEATURES OF LED 7-SEGMENT 0.56″ RED CC 3-Digit:

• 3-digit 7-Segment display with common cathode (CC)
• 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

Each digit of these displays have 7 separate LEDs comprising the 7 segments of the digit 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 cathode (CC) type which means that all 8 of the LEDs in each of the 3 digits have their cathodes tied together and these are pulled to ground to enable that digit.   These connections are labeled DIG1, DIG2 and DIG3 in the drawing.

To light a particular segment, the control (anode) pin for that segment is driven HIGH.  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 ground 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 connections for each of the individual segments such a ‘A’ are connected together in all 3 digits, so the displays are designed to be used in a multiplexed fashion unless you want all 3 digits to always show the same number or character which generally isn’t all that useful.

Multiplexing means that the ground connection (DIG1-DIG3 )for each of the displays is enabled sequentially by driving it LOW while the data for that particular digit is driven HIGH on the 8 LED lines.  This is repeated for each of the digits very rapidly so that all of the digits appear to be operating continuously.

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.

At an operating voltage of 5V, a series current limiting resistor of 150 ohm will provide max brightness if driving these displays in a static mode rather than in a a more typical multiplexing mode.

When you are using displays with multiple digits in a multiplexed mode where each digit 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 60 mA.  In that case, you generally want to drive the display with more current since each digit in the display is on only a portion of the time and will therefore appear dimmer than if the digit was being driven constantly on.  For that application, a resistor value of 50 ohms will provide max brightness. Values in the range of 75-91 generally work pretty well when max brightness is not required.

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 digit in the module.  If there are multiple digits, the number of required output pins on a uC increases quickly.

Fortunately, there are ICs like the MAX7219 that are made to interface with these modules and make life a whole lot easier.  Communication between the MAX7219 and the uC is made over the I2C bus and the MAX7219 takes care of updating and multiplexing up to 8 of the 7-Segment modules using only 3 pins on the microcontroller.  They also provide on/off and brightness control and multiple ICs can be daisy-chained together for even larger displays.  These ICs are available below.

Notes: 

1. None

Technical Specifications