HOW TO DEVELOP A PROJECT
Before we explain the features of each item, we need to cover how to develop a project. There are a number of prototyping systems on the market such as solderless breadboard, matrix board, strip-board, perf (perforated) board. Here are a few pointers on their suitability.
Solderless breadboard has two main problems. The connections become very loose after the parts have been inserted and removed a number of times, mainly due to the different thickness of the leads and it is easy to knock a component out when you are working on a project. Loose connections also produce a lot of noise and this can be interpreted by the microcontroller as “pulses” and upset the operation of a circuit.
Strip Board and any boards that consist of strips of copper track, need a lot of cutting to separate sections of the track and this makes the board useless for re-use. It also makes the project much larger than needed, due to the blank holes needed between cuts. I would be laughed out of the office if I produced a project in this format. It is just not professional and the strips force you to make the project to suit the board and not the board suit the project.
Matrix Board is one alternative but it has its problems too. It has to be constantly turned over to carry out the wiring between the components. In addition, the components are difficult to remove if a modification has to be made. Matrix Board is suitable for building a project that has already been designed. It is not suitable for developing a project.
One solution is the “birds nest” or “rats nest” approach. The Experimenter Board MkIII has been designed for this mode of construction. It has no holes and all the components are soldered on the copper side of the board, from one land to another. It’s a jumble of components but you can see the whole circuit at the one time. I have found it eliminates a lot of mistakes and is much easier and faster than anything else. It also forces you to make a proper printed circuit board as you cannot use the “jumble” for the finished design.
Paul, our producer of the PC layouts for Talking Electronics, does not use the prototype when CADing the track-work. He only needs a circuit diagram and the size of each component. This means the presentation of the prototype does not come into any other stages of development and thus its main feature is ease of construction and modification. Once you use the Experimenter Board MkIII, you will know what I mean.

The three boards/modules are available for building a prototype:
1. Experimenter Board MkIII. This board has no holes and the components are soldered from one land to another. An IC socket is soldered in the centre of the board and the components are placed around the chip. The board is only small, however it can take either a ‘508A or F84 microcontroller and one additional 16 pin chip.

THE CIRCUIT
The circuit for the Pseudo ‘508A is shown above. The three clock frequencies for the Project-Under-Development are generated by the components around the 8-pin chip. The basis of this module could be any chip containing gates but we could not get any other 8-pin chip to do the job. In addition, it would require a lot of surrounding components to generate the features we need. The answer was to use a PIC12c508A.
It contains two programs: The “STEP” program, made up of a single step feature, then a 10Hz repeat after 2 seconds and a program that produces a variable output frequency according to the position of the 50k pot.
The program is constantly looping the two switches and when ST button is pressed, it outputs a clean pulse to the PICF84, via a gating diode. This will advance your program one step (one instruction) and you can see exactly what is happening after each instruction is executed. It’s absolutely fascinating to see a program going through each step and if the button is kept down, 10 instructions per second are executed.
If the RC button is pressed, the program in the ‘508A outputs a low on GP1 and looks to see when GP1 is HIGH. When it is HIGH, it outputs a pulse to the F84 via pin 5. If the pot is turned clockwise, it will have a lower value of resistance and the capacitor in the TIME DELAY circuit will charge at a faster rate. This will be detected by the ’508A and the output pulses will increase.
If the XT button is pressed, the crystal will be connected to the PICF84 and your program will run at crystal frequency.

Building the Pseudo ‘508A
All the components fit onto the PC board as shown on the overlay.
A length of ribbon cable is connected to the 8 holes at the edge of the board and the other end is soldered to an 8-pin IC socket. The wires are soldered to the top of the socket and you must be very quick with soldering to prevent the socket melting. Make sure you use an 8-pin IC socket with straight pins (some sockets have bent pins to allow the socket to hold onto the board when inserted). These pins will also damage the socket on your project.

Using the Pseudo ‘508A Module
You will need these things:
1. The 508A project you are developing, such as on the 12C508A 6v Express module, or one of our ’508A projects.
2. The Pseudo 508A module,
3. A blank PIC16F84 chip,
5. Notepad or Text Pad, for writing your program,
4. Multi-Chip Programmer or 5x7 Display for burning the chip,
6. IC-PROG software - the program that runs the burn routine.