Nuts and Volts - November 2014

• If you use the same RazzPi- 20 board in both PICAXE-Pi and pure PICAXE projects, make sure the jumpers on the two three-pin headers are in the correct position for your current project.

• If you never intend to use the RazzPi- 20 in a PICAXE-Pi project, you could assemble the board without the two three-pin headers, and replace each one with a soldered-in wire jumper that connects the two lower positions for each three-pin header.

RazzPi- 20

Assembly Instructions

Since the RazzPi- 20 board can be used with both PICAXE and PICAXE-Pi projects, let’s take a look at the process of assembling the PCB. A complete parts list is shown in Figure 13, and all the parts (except the PICAXE processor) are available on my website. (PICAXE processors are available at www.phander son.com and www.sparkfun.com.)

As usual, read through the following list of assembly instructions to be sure you understand the entire procedure before beginning to put the board together.

1. On the top of the board, install the diode (observing polarity), the two three-pin headers, and the stereo jack. (Do not install the IC socket yet.)

2. Snip excess leads on the bottom of the PCB.

3. On the bottom of the board, install the SMD cap and the three SMD resistors.

4. Insert headers H1, H4, and H5 into the middle area of a breadboard so their positions match the spacing on the PCB layout.

5. Place the PCB on the three headers so that the short ends of all the pins are inserted into the corresponding holes in the PCB.

6. Solder headers H1, H4, and H5 in place.

7. Remove the PCB from the breadboard and insert headers H2 and H3 into the upper power rails of the breadboard so their positions match the spacing on the PCB layout.

8. Place the PCB on headers H2 and H3 so that the short ends of the header pins are inserted into the corresponding holes in the PCB.

9. Press down on the PCB so all the headers are fully inserted into the breadboard.

10. Solder headers H2 and H3 in place. (Header H2 will require extra care because the available space is very limited.)

11. Remove the PCB from the breadboard, insert the IC socket from the top of the PCB, and solder it in place on the bottom of the board.

12. Clean the top and bottom of the PCB.

Experiment 1: Implementing a Pure PICAXE Setup With the RazzPi- 20

In this experiment, we’re going to implement a 15 LED “Cylon Eye” project as a simple demonstration of how to use the RazzPi- 20 board in a pure PICAXE project. Figure 14 is a photo of my breadboard setup for the experiment. In addition to the power supply and the RazzPi- 20, the only other components we need are two 10-bar LED displays, two 10-pin SIP resistors (nine 470Ω resistors each, with a common ground pin), and four jumper wires. The setup is simple. The two LED bar displays are lined up so that the anode of the left-most LED is connected to pin C. 4 on the RazzPi- 20, and the two SIP resistors are installed so that their ground pins are at opposite ends and connected to ground with a short jumper. (The ground connection on the left end is one breadboard position to the left of the first LED.) In Figure 14, you can also see how the two slightly longer jumpers connect pins C. 7 and C. 5 on the RazzPi- 20 to LEDs #6 and #7 (counting from the left), which would otherwise not be connected to a 20M2 output pin. Of course, we can’t use pin C. 6 for this experiment because it’s fixed as an input. As a result, we’re using eight pins on port B, and seven pins on port C to implement our 15 LED Cylon Eye. Finally, Figure 14 demonstrates the amount of space the RazzPi- 20 saves on a breadboard. Without it (or a similar PCB), there would be no way we could install a 20-pin processor and two 10-LED bars on the small breadboard we usually use in our projects.

When you’ve completed your breadboard setup, download the software for this experiment ( Cylon15.bas) to your 20M2, and have fun watching the Cylon Eye scan back and forth!