Introduction
Seven segment displays are the simple form of displays used to display decimal numbers. They come into picture when there is a need for counting like applications in the projects. Seven segment board contains 4 displays and it can be interfaced to any port using the FRC cable provided with the OpenLab. It needs two ports for operating the board, one for selection and another for segment control.
There are four seven-segment display modules in an OpenLab unit. They are mounted on a board on which data and control ports are fixed at the top right corner separately. A single seven segment display module is a combination of eight LEDs including a decimal point. Decimal digits and some alphabets can be displayed by the seven segment display module.
One of the important features of a seven segment display module is that each module has an enable or disable circuit associated with it. With the help of the firmware, so we can enable or disable a single module in firmware. Four seven segment displays and 8 transistors are arranged like arrays. So each section is separated. The 8-bit data port is shared between four modules. Control port uses four bits and is connected to cathode pins of each seven segment display. These pins determine which module is enabled or disabled at a particular time depending on control bit status from microcontroller port.
Operation
Seven segment display board contains 7 segments and a decimal point. Each data port represents a segment in the display. The segments are controlled through the firmware. The pins are configured in active low. The first pin represents A, the second pin represents B and so on.
The displays used in OpenLab are common cathode displays, but all the input connections are inverted because of driving circuits. That is, even if it is a common cathode display, it operates like a common anode display. In common cathode displays, the common pin is grounded and other pins are given high based on the requirement. In our case, a common pin is grounded while we activate the segment by giving ‘0’.
Circuit
Below is the circuit of a 7 segment display unit. The segments are driven by PNP transistors. So the segments can be activated by applying a low on the base of the transistor (data port J3). The ground pin is controlled by an NPN transistor, so the module can be activated by giving a high (control port J2).
Display Codes
Display codes for the digits are given in the below.
Data Port
Data pins are active low. That means, grounding the bit will enable the segment LED and giving a High signal will disable the segment.
Control Port
J2 pins are active high. Giving High on the bit will enable the seven segment.
NC – No Connection
Power Header
There is a power header available in this board, J6. This can be used to test the display.
Seven segment display board is one of the output devices shipped with OpenLab usually used to display the numerical values using the seven segments. The board consists of 4 seven segment modules namely U1, U2, U3, and U4. All the other control circuits are included in the same board including the connectors.
The above image shows the seven segment peripheral board on OpenLab. The board is activated by turning on the switch on the top left side. The seven segment board is controlled by port A and port D by default. The strip on the top provides 5V and GND.
Connect the control port to port A using FRC cable. The control port which is controlled by port A by default can be altered using the program.
Then connect the data port to port D using FRC cable. The data port is controlled by port D by default and can be altered with the help of the program.
These two port strips are used for debugging purposes. After completing the connections, the output should be displayed on the board.