Using a TestRig
Whilst working with the PIC microprocessor, I find that it is useful to populate a small piece of strip board or 'perf board' with the basic requirements of any project - the PIC processor, power in, decoupling capacitors, clock, serial i/o and some form of indicator.
This board then can be used as the basic building block for any experiment. Several pre-made and bare PCBs can be obtained from companies like Forest Electronics, these development boards contain a combination of the above elements.
The problem (I find) is that you get your board hooked up to an experiment, test the software, and then another idea or project comes along before you have had a chance to finish the ongoing project. The first impulse is to hang the necessary bits off the existing board and re-program the PIC. This is fine, up to a point, that point occurs just after you have re-wired the board a few times, and a couple of the wires to your original board come adrift.
A pre-made board with dedicated a prototype area will last longer when used in this way, but it is still going to suffer with all of the extra handling involved.
I was testing several LCD displays a while ago when I decided to do something about it. The junk box contained several 25pin parallel plugs and sockets (the type used for the printer connections on a PC, or the even older 25pin RS232 connections). Using a short piece of ribbon cable, I wired the free port pins ignoring the pins that are required by programming, the crystal and RS232 io. This left me with a few pins for power and ground connections.
Housing the board in small box with the 25pin connector mounted on one edge, the RS232 cable emerging from a notch cut in the opposite edge.
This particular box had enough room for a 9v Battery, so I included that and mounted a small On/Off switch.
Using a spare 25pin plug, I wired the LCD display and uploaded a test program - It worked a treat.
Now I can hang the necessary wires on a spare 25pin plug, upload a test program and I'm away - no more handling of the board, no more knocking off one wire whilst I try to solder another. This method will obviously not be suitable where the noise generated by one port pin interferes with another - due to the extra cable lengths and use of a ribbon cable.
The pinout used does not matter, although, if you keep the port pins together, it can make wiring easier. If you were to use a dedicated input port and wanted to reduce the effects of noise in the ribbon cable, you would route the wires either side of the input line to 0v so that they acted as a minimal shield from the other lines. For longer cables, it would be wise to use a wider cable and wire every other line to 0v. In my unit, I simply kept the cable fairly short, and it works quite well.
Introduction
About the PIC Processor
Programing the PIC
Building Blocks
PIC Test Rig
Connecting an LCD
VoipDeskPhone
VoipDeskPhone the Software
VoipDeskPhone3 Changes for use as an Asterisk Console Phone
Cheap PIC Keypad PoundShop Clock / Alarm = Cheap Keypad
3 State LEDs
Add DRAM to a PIC
PIC Links
