Sep 02 2017

4 Character 7 Segment Display

I built another handy circuit to ‘house’ a 4 character 7 segment display. It looks like this:

4 Character 7 Segment Display

Basically it just ‘breaks out’ the 16 pins of the display with two 8 pin female headers. Pins 1-8 are connected to the header at the bottom and pins 9-16 are connected to the header at the top. Note that 6 220 Ohm resistors are needed to protect the LEDs.

 

 

The Fritzing diagram to the right (Download Link) shows which pins select which character (colon or apostrophe) is selected to turn on and thus needs a resistor. The LEDs actually light a bar shape. Each ‘character’ is composed of 7 LEDs (or segments). The image below shows what each of the pins controls.

4 Character 7 Segment Display Pins

 

 

 

 

The LED pattern is as follows:

 

7 Segment Display4 Character 7 Segment DisplayFour of these characters go together to be able to display things like time, temperature, voltage, etc.

 

 

The technical manual is HERE. The pin functions (1-8 bottom and 9-16 top) are as follows:

Connecting this 4 character 7 segment display to an Arduino is usually done in conjunction with 1 or more  shift registers due to having so many wires. Connecting without the shift register, an arduino looks like it needs a ‘hair cut’ with so many ‘wires’ all over the place.

4 Character 7 Segment Display

4 Character 7 Segment Display

 

 

 

 

 

 

 

I connected my 4 character 7 segment display circuit with two 74HC595 (shift register IC)  breakout modules. Each 74HC595 module controls 8 pins (1 shift register for the bottom 8 pins and one for the top 8).  With these modules, only 3 wires (besides power and ground) connect to the Arduino.

4 Character 7 Segment Display

 

Using an Arduino library designed for the 74HC595 shift register makes it easier to control the display. I like this shifter library hosted on GitHub. With it, each pin is easily referenced by number.

 

 

Here is a an Arduino sketch I created to display current voltage on the 4 character 7 segment display :

Notice that I created functions to select the specific character to turn on and a function to turn on the LED segments needed to display each number digit. With the shifter library and these functions, you are all set to make something interesting! How about a multimeter?

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