Nuts and Volts - October 2010

■ PHOTO 7. Cover slot.

module and keypad, based upon how you will be mounting the finished project. Note that you must use a keypad with individual connections for each of the 12 keys and one common connection; I recommend using the Velleman 12- key keypad. Since I intended to house everything in a project case, instead of using ribbon cable I soldered a set of 14 male header pins to the underside of the keypad (i.e., the side without the keys). Photo 6 shows these header pins will connect to the BS2 module pins 4 through 15 on final assembly.

Next, solder an adequate length of hookup wire to pin 1 of the keypad to allow it to connect to Vdd on the BS2. The power switch is an SPST toggle connected between the nine-volt battery’s positive terminal and Vin. Connect the battery’s negative terminal to Vss. The DTMF/MF switch is an SPST toggle connected between P1 and Vdd. The Aux button is an SPST N.O. pushbutton switch connected between P2 and Vdd. The Audio output jack’s center conductor is connected to P0 via a 220-ohm resistor and the shield ring to ground. Connect the 1 µF electrolytic capacitor’s positive leg to the center connector of the Audio jack and the negative side to the Audio ground terminal.

Since I wanted to package the encoder inside a small ( 5” L x 3” W x 2” H) project case, I connected the keypad and BS2 module by sandwiching them on opposing sides of the case lid and joining them via their respective header pins through a slot I dremeled into the lid. (I attached the back of the keypad to the outside of the lid with a plumber’s adhesive known as “Goop;” the BS2 module was supported inside the lid with a thin piece of Styrofoam and glued in place. Be sure that pin 3 of the keypad is connected to pin 4 of the BS2 module, continuing to connect the pins in a row so that pin 14 of the keypad connects with pin 15 of the BS2, leaving pins 1 and 2 of the keypad unconnected (see Photos 7 through 9). However you package the hardware, make sure the DB9 connector

■ PHOTO 9. Keypad/BS2 connection interface (shown without case for clarity).

■ PHOTO 8. Styrofoam PCB support pad attached inside cover.

on the BS2 module will be accessible for programming. Assembly of the PhreakEncoder hardware is now complete (Photo 10)! Now, finish the build by loading the software.

Load the Code and Test It Out

Connect the PhreakEncoder to your PC via the serial cable and use the BSE to load the PhreakEncoder.bs2 firmware (also on the NV website) onto the device. Connect a small eight-ohm speaker of your choice via the Audio output jack and turn on the power. With the DTMF/MF switch in the DTMF position, the keypad will produce standard telephone touchtones of 200 milliseconds duration. (If you do not hear tones in the speaker, check all wiring and connections against the diagram, and be sure