PIC Tutorial Main Board
Main Board
This
is the circuit of the main board for the tutorials, it consists of the
PIC16F628, a 7805 regulator, 3 capacitors, three ten pin connectors, one
for PortA, and two for PortB (the second for connecting two of these
boards together), and a two pin ground test connection - optionally it also includes an LED, a
resistor, and two 2 pin jumpers. Each of the three ten pin connectors is wired
identically, with a ground connection at the left side, and a 5V
connection at the right - this will allow you to plug the same extension
board into either port, and help to demonstrate their differences. The
capacitors C1 and C2 are to keep the 7805 stable, they have a tendency to
oscillate without them, and C3 is just a decoupling capacitor placed near
the chip, always a good practice (although PIC's do seem very tolerant of
them). The jumpers J1 and J2 allow the LED to be connected either to 5V
(J2) as a 'power on' indicator, or to RB7 (J1) where it can be switched by
the port pin - this allows you to do something before you build any
further boards. Under no circumstances connect both J1 and J2 at the
same time, it's likely to damage the chip.
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This
is a photo of the main board, it's built on a piece of Veroboard
23 strips wide, by 31 holes high. The left of the two black
connectors at the bottom is PortA, the right pair are PortB. All the
wire jumpers are required to line the connectors up neatly. In
order to prevent the pins of the PIC getting damaged, the PIC is
permanently inserted in a 'turned pin' socket, this is then
plugged into a normal socket on the board. To program it the PIC,
complete with turned pin socket, is unplugged and inserted in the
programmer, programmed and then returned. This is very easy to do,
and the 'turned pin' socket prevents any damage. The PIC is
capable of being
programmed in-circuit, but it adds circuit complications and uses
up I/O pins, so I haven't implemented that. J1 is the upper of the
two jumpers, nearest the LED. Although it's not very easy to see
in this picture, pin one of the PIC is to the left. The 2 pin
ground test connection isn't fitted in this picture, it fits
vertically just above C3, on the ground rail connecting to the
negative end of C3. |
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This
is a bottom view of the board, I've indicated the track cuts (19
of them) with blue circles, with this picture, and the one above,
it should be fairly easy to duplicate the board - remember - there
are 19
track cuts, and 21 wire links. |