Nuts and Volts - October 2010

■ PHOTO 1. BS2 OEM kit parts.

the BS2, but I chose this module because it is strongly supported with free tutorials and programming documentation from the Parallax website and numerous online user groups. It programs in PBASIC which is easily learned by hobbyists who are not experienced in programming. After you’re finished experimenting with the project described here, you will have the confidence and skills to re-use the BS2 in other projects with programs you create!

With the BASIC Stamp, FREQOUT and DTMFOUT do all the work

The kit for the BASIC Stamp 2 OEM module (Parallax part number 27291) is easy to assemble even for the novice builder, and includes a PCB (printed circuit board) with all the components and their locations clearly marked. It is easily programmed via the on-board serial port in the PBASIC language developed by Parallax. One of the unique features of the BS2 is its ability to generate standard touchtones, as well as custom MF tones using the PBASIC commands DTMFOUT and FREQOUT which make it possible to generate both standard telephone Touchtones as well as any other single- or dual-frequency tones and sequences. This micro module is well supported with free reference materials and IDE (Integrated Development Environment), and serves as a good intro to microcontrollers and their practical uses (which will doubtless spur the user to devise project ideas of their own). Finally, the BASIC Stamp 2 is available from a number of sources.

Here you’ll learn how to interface the BS2 module with

■ PHOTO 3. Header pins (top view).

■ PHOTO 2. Header pins (bottom view).

a keypad, a few switches, and a handful of discrete components, then load free open source firmware to make your own unlimited tone generator box. The concept is simple: The hardware checks the state of the 12 keys on the keypad in a continuous cycle, along with monitoring the state of the toggle and pushbutton switch; it then instructs the BS2 to generate the appropriate touchtone or custom tone(s) output via pin 0. By simply changing the values in the software and loading it onto the BS2 via the integral serial port, you can generate any single- and multi-frequency tone(s)/sequences without changing the hardware. Tone frequency, duration, pauses, and sequences can all be modified according to your needs. (More on the programming later.) Now, let’s build the PhreakEncoder!

The Build

Step 1: Assemble the BS2.

The BS2 OEM version comes complete with the PCB and all necessary parts, and costs about $30 for the kit form. (See Photo 1.) Assemble the module according to the directions from Parallax ( www.parallax.com); however, do not install the bank of 16 angled male header pins on the lower edge of the board. This will permit direct wired connections between these BS2 pin connections and the keypad and control switches later.

There are several approaches you can use to assemble this project. You can breadboard the BS2 and related components if you intend on building the project as a temporary setup. Or, if you’d like a more permanent assembly you may want to house everything in a project case like I did.

I chose to sandwich the BS2 module and keypad on opposite sides of the project case lid. I soldered in a divided row of 16 female header pins on the output tabs of the BS2