Improved circuit with Input side and Reset.

This modified circuit has the following changes:

An Input side which consists of a 7805 voltage regulator, input connector J1, an ICSP connector, J2 for programming the PIC without removing it from the PCB(which in turn avoids a lot of soldering work) and a reset connector, J3 for resetting the microcontroller.

SIL (Serial In Line) connectors are used for this purpose.

The ULN 2003A is a high current Darlington Array used to drive the LED matrix.

The PIC Microcontroller may provide current upto a few milli-amperes, it may be sufficient for driving a few LEDs but in case of a 5 X 7 LED Matrix, there are 35 LEDs and hence the drive current provided may be low. Hence the ULN 2003A current driver IC is used for this purpose.

While running the simulation I found that the output of the ULN was not changing and hence the Matrix Display was not working properly. The idea of the OR Gates then came into picture ( The working of the matrix display and the uselessness of OR gates will be explained later). The presence of the OR gates made the simulation work well.

However the difficulty of OR gates comes into picture while taking a single side PCB layout.