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How to Display Decimals Using LED Numbers

LED numbers are known as 7-segment displays. They are made from light-emitting diodes (LEDs) that form segments which combine to make numbers. Calculators, ovens and stereos are examples of devices where the displays may be found. LED numbers may be driven with digital switches, such as decoders. They may also be driven manually. Some of them can show decimals as well as numbers, where the decimal appears on the top part of the casing. To display a decimal using LED numbers, identify the display type and the location of the decimal segment. Practice with a manually driven display.

Things You'll Need

7-segment LED display
Datasheet
330-ohm resistor
Pushbutton switch
2 AA batteries
Battery holder
Solderless breadboard
Jumper wires

Instructions

- 1
  Identify the 7-segment display type. Common anode types have the anodes, or positive LED leads, joined together. Common cathode types have the cathodes, or negative LED leads, combined together.
- 2
  Find the location of the common connection and the location of the LED that controls the decimal point. To do this, use a datasheet. For example, there may be two common connections at pins 3 and 8, and either one can be used. The datasheet may label the decimal as DP and show its location as pin 5.
- 3
  Choose a row on the breadboard for the positive voltage source and another as ground. Insert the red lead of the battery holder into the positive location and place the blue lead at ground.
- 4
  Place the segment vertically into the breadboard, so that its top row is in the upper section, and its bottom row is in the lower section. For this circuit, a common cathode type is assumed, so place a jumper wire between the common cathode connection and ground. For example, if the common connection is at pin 3, place one end of the wire into pin 3's column and the other end of the wire into one of the holes at the ground row.
- 5
  Insert one end of a resistor into the decimal point's column. Place the other end of the resistor into a column that is unoccupied. Add one end of the pushbutton switch to this column and add its other end to the row that the red lead of the battery holder is in.
- 6
  Insert the batteries into the holder. Push the button and the decimal will light.

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