■ 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
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.
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
October 2010 55