PIC Tutorial Main Board Three

Main Board Three

This is the circuit of the third main board for the tutorials, it consists of the PIC16F877, a 7805 regulator, a 20MHz crystal, 6 capacitors, five ten pin connectors, one for PortA, one for PortB, one for PortC, one for PortD and one for PortE . Each of the five 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 any port, and help to demonstrate their differences - the most obvious differences are that PortA only has 6 I/O lines, which can be either digital I/O or analogue inputs, with 10 bit resolution, and that Port E only has 3 I/O lines.

Basically it's very similar to the 16F628 tutorial board, but has extra ports and added facilities - as the 16F877 doesn't have an internal oscillator a crystal is required for the clock oscillator - I choose a 20MHz crystal for this, if you can't get a 20MHz chip the 4MHz 16F877's seem perfectly happy to run at 20MHz - I suspect they are exactly the same chip, and graded to provide the two different versions.

I used a 100mA regulator IC, a 78L05 - because I happened to have one, but a 7805 1A regulator would do just as well, and give more power availability for extension boards.

This is a photo of main board 3, it's built on a piece of Veroboard 34 strips wide, by 45 holes high. The left of the three white connectors at the bottom is PortC, the right one is PortB, and the middle one PortD, at the top the left one if PortE and the right one PortA (I stuck little labels on them as I keep forgetting which is which). 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.
This is a bottom view of the board, I've indicated the track cuts (50 of them) with blue circles, with this picture, and the one above, it should be fairly easy to duplicate the board - remember - there are 50 track cuts, and 31 wire links.

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