22-03-2014, 02:17 PM
5 X 7 LED Matrix Display Project V1.0
[attachment=60412]
[b]5 x 7 Display Explanation[/b]
2Only one column (vertical) of LEDs turns on at a time. Seven of the lines of port B drive
the LEDs via 100R resistors and the cathodes are connected together and taken to the
0 V rail via a "sinking" transistor. The 5 sinking transistors are turned on (one at a time)
by the outputs of a CD 4017 "counter" chip. This chip has 10 outputs with one output
going HIGH at a time. The chip is firstly reset by taking pin 15 HIGH then LOW and
keeping the line low - this allows the chip to "clock."
The first output (pin 3 on the 4017) goes HIGH and this is connected to the first
transistor via a 2k2 base resistor. The transistor turns on and the cathodes of the first
column of LEDs connect to the 0v rail.
The LEDs are turned ON by delivering current from the PIC chip. When any of the
output lines of the PIC go HIGH (RB0 to RB6), the corresponding LED(s) are illuminated.
The 100R resistor limits the current to about 25 mA, as this is the maximum each
output is designed to deliver.
The output lines of the chip correspond to Port B and by turning off these lines, clocking
the 4017 then turning on the outputs again, the second column of LEDs will be
illuminated.
[attachment=60412]
[b]5 x 7 Display Explanation[/b]
2Only one column (vertical) of LEDs turns on at a time. Seven of the lines of port B drive
the LEDs via 100R resistors and the cathodes are connected together and taken to the
0 V rail via a "sinking" transistor. The 5 sinking transistors are turned on (one at a time)
by the outputs of a CD 4017 "counter" chip. This chip has 10 outputs with one output
going HIGH at a time. The chip is firstly reset by taking pin 15 HIGH then LOW and
keeping the line low - this allows the chip to "clock."
The first output (pin 3 on the 4017) goes HIGH and this is connected to the first
transistor via a 2k2 base resistor. The transistor turns on and the cathodes of the first
column of LEDs connect to the 0v rail.
The LEDs are turned ON by delivering current from the PIC chip. When any of the
output lines of the PIC go HIGH (RB0 to RB6), the corresponding LED(s) are illuminated.
The 100R resistor limits the current to about 25 mA, as this is the maximum each
output is designed to deliver.
The output lines of the chip correspond to Port B and by turning off these lines, clocking
the 4017 then turning on the outputs again, the second column of LEDs will be
illuminated.