Nuts and Volts - February 2009

PICAXE PRIMER

SHARPENING YOUR TOOLS OF CREATIVITY

■ BY RON HACKETT

IMPLEMENTING A SERIAL DATA LINK WITH THE IR MULTI-BOARD

IN THE TWO PREVIOUS INSTALLMENTS OF THE PRIMER, we constructed a stripboard version of the IR Multi-Board: an I/O module that can implement the full range of PICAXE IR capabilities. We also developed a simple IRMB-based object detection circuit for use in a robot or a home control system, as well as an interface that received and decoded the signals from a universal TV remote programmed to transmit the Sony IR Control (SIRC) protocol.

This month, we're going to resolve the problem of the missing key-presses that we had last time with our SIRC system and then move on to accomplishing our final goal for the IR Multi-Board: using two IRMB modules to implement a wireless serial data link for use in our projects. We'll be using the same setup we worked with last time, which consists of our standard 28X1 Master Processor circuit with one IRMB set up as a peripheral input device and a second IRMB installed on a mobile battery-powered breadboard for range testing. In addition, we'll make use again of a TV remote capable of transmitting in

the SIRC protocol. Our experiments will involve the following programs:

• Hserin TestAll.bas

• Hserin TestInt.bas

• RMBrxSIRC.bas

• IRMBserin.bas

• IRMBserout.bas

To save you the trouble of typing them into the Programming Editor, these programs are all contained in one ZIP file that is available on the Nuts & Volts website (

www.nuts volts.com). If you prefer, you can email me at Ron@JRHackett.net and I'll send you the file. In order to make our discussion here easier to follow, it would be a good idea to get the

file and print out the five programs before you read much further.

CAPTURING THE MISSING SIRC KEY-PRESSES

■ FIGURE 1. IR Multi-Board schematic.

In our last experimental setup we programmed an IRMB to receive IR signals from a SIRC TV remote and relay the data to our 28X1 Master Processor. The 28X1's program was fairly simple and somewhat limited in that it was only capable of capturing a single key-press in the background; any additional key-presses that occurred during one blink of the LED were lost.

Our first setup this month will fix that problem. In order to do so, we will use the same physical setup with new (and improved) software. Output1 of the IRMB is again connected via a 4.7K resister to input 7 (the hserin input) of the 28X1. Its program ( IRMBrxSIRC.bas) is essentially the same as the IRMB_Remote.bas software that we used last time. The improved functionality is implemented in the 28X1's Hserin TestAll.bas software, which requires a brief explanation before we actually try it out.