This bulletin will deal only with the b asic contruction, troubleshooting and
adjustment of the bl ue box. If you would like to know the specific job of a
ny part in the circuit just write me a msg and I will b e glad to ans- wer it.
We all know that the touch tones freque ncies are composed of two tones (Two
different freqs.) so t hat is the reason why we have 2 VCO'S ( Voltage
controlled oscilators). We will call these VCO#1 and VCO#2. If you have
noticed VCO#1 and VCO#2 are exactly the same typ e of circuits. That is why
only one was drawn. But reme mber that whatever goes for VCO#1 also goes for
VCO#2. Both VCO'S are composed of a handfull of parts. one chip two cap
acitors 2 resistors and five potentiometers. All of this wil l give you (when
properly calibrated) one of the freqs. necessary (the other one will come
from VCO#2) for the operation of th e BB. Both of these freqs. will be mixed
in the speaker thus forming the required tone.
This is one of the most sophisticated de signs I have ever made. Why?. because
other designs will drain t he battery after 10 - calls! This design will make
them last 1 0 months!!!!!!. But never the less don't forget to put in a
switch for on and off. Ok let's build the two VCO'S and calibr ate the unit
before we get to the keyboard contruction.
VCO CONTRUCTION
=== ===========
TOOLS REQUIRED
1 ocilliscope (recomended but not re quired)
1 Freq. counter (REQUIRED)
1 Volt meter " " "
Electronics tools (Pliers,drill, scre wdrivers, etc)
PARTS
R1 1.5K RESISTOR 5%
R2 1K RESISTOR 5%
C1 .1uf ELECTROLYTIC CAPACITOR 16V DC
C2 .01uf ELECTROLYTIC CAPACITOR (MYL AR) 16VDC
IC1 2207 VCO CHIP BY EXAR ELECTRINI CS
remember the above it is only for VCO#1 but the same goes for VCO#2.
R3-R4 150 OHM RESISTORS 5%
C3-C4 .1 uf ELECTROLITIC CAPACITOR 10VDC
P1-P10 200K TRIMMER POT - 20 TURNS
DIODES USED IN THE KEYBOARD ARE 1N914 TYPE (40 OF THEM)
AND 13 SWITCHES FOR THE KEYBOARD SPST. MOMENTARY.
SPKR= YOU CAN USE A TELEPHONE SPEAKER FOR THIS(IT WORKS BEST)
BUT REMEMBER TO TAKE OUT THE DIO DE THAT IS CONNECTED
ACCROSS IT.
**************************************** ************************
IMPORTANT NOTES
1 DO NOT USE ANYTHING ELSE THAN A MYL AR CAPACITOR FOR C2
2 PINS 10,9,8 SHOULD BE TIED TOGETHER AND BE LEFT FLOATING.
3 ALL RESISTOR SHOULD BE 5%! NOTHING ELSE
4 A TELEPHONE SPEAKER GIVES THE BEST RESULTS
**************************************** *************************
TROUBLE SHOOTING
By now you should have constructed the two VCO'S on a bread board or anything
that please s you.
Check for cold solder joints, broken wi res, polarity of the battery,
etc.........
Before we apply power to the VCO'S we h ave to adjust the pots for their half
way travel point. This is done by turning them 21 turns to the right and then
10 turns to the left. Do the same for all ten of them.
Now apply power to the unit check to see that you have power in the chips by
putting the positive lea d of your volt meter on pin 7 and the negative lead
on pin 12 . If you don't have anything there turn off the unit ant REC HECK
THE WIRING.
When you get the right voltages on the c hips, connect a diode to a piece of
wire (look at fig. 2 for the orientation of the diode) from ground to any pot
at point T (look carefully at the schematic for point T it is label ed T1-T10
for all pots) You shold be able to hear a tone, if no t dissconnect the lead
and place the speaker close to your ear and if you hear a chirp like sound,
this means that the two VCO' S are working if you don't, it means that either
one or both of the VCO'S is dead. So in this case it is allways good to ha ve
an ocilloscope on hand.
Disconnect the speaker from the circuit and hookup the ocilliscope to one of
the leads of the speaker and t he ground from the scope to the ground of the
battery. Connect ag ain the ground lead with the diode connected to it from
grou nd to any pot on the VCO that you are checking and you should see a
triangle wave if not turn the pot in wich you are appl ying the ground to
until you see it. When you do see it do the the same for the other VCO to
make sure it is working. (a mplitude is about 2VAC)
When you get the two VCO'S working you a re set for the adjustment of the
individuals pots...
ADJUSTMENT
Disconnect the speaker from the circu it and connect a freq. counter (the
positive lead of the counte r to one of the speakers leads that belongs to
VCO#1 or connect i t to pin 14).
Connect the negative lead to the batt ery negative and connect the jumper
lead with the diode f rom ground to pot number 1 T1 .( The first pot number 1
point T1) If you got it working you should hear a tone and get a reading on
the counter. Adjust the pot for a freq. of 1700hz and continue doing the
same for pots 2-5 except that they get d ifferents freqs.
Now disconnect the freq. counter from t he speaker lead of VCO#1 or from pin
14 (which ever you had it attac hed to at the beginning) and connect it to the
speaker lead of VCO#2 or to pin 14 of VCO#2 and perform the same adjustments
to P6-10.
When you finish doing all of the pot g o back and recheck them again.
KEYBOARD
If you look at fig-2 you will see that the keys are simple switches connected
to ground and two diodes on th e other end. These diodes are used to simplify
the construction of the keyboard because otherwise the distribution of the
ground signal fo r both VCO'S would have been done mechanically. One diode
will go to VCO#1 and the other will go to VCO#2. Fig-3 shows the arrangement
of th e keys on the keyboard.
Below is a table that will hel p you connect the keys to required
VCO'S pots.
TO TO FREQ OUT FREQ OUT
KEY POT ON VCO1 POT ON VCO2 PIN 14 VCO1 PIN 14 VCO
C 1 6 1700 1100
0 2 10 1300 1500
E 1 10 1700 1500
1 4 7 900 700
2 3 7 1100 700
3 3 8 1100 900
4 2 7 1300 700
5 2 8 1300 900
6 2 6 1300 1100
7 5 7 1500 700
8 5 8 1500 900
9 5 6 1500 1100
X - 9 ---- 2600
**************************************** *******************************
* REMEMBER THAT FIG-2 IT IS THE SAME FOR EACH KEY EXCEPT THE "X" WHICH*
* ONLY TAKES ONE DIODE. *
**************************************** *******************************
As a final word you can build this in any type of enclosure and should never
be used to make free ca lls using the telephone lines. I hope this bulletin
will clear a ny question you may had on the blue boxes.
If you have any question please
leave me a msg. and I will be very glad to
answer it.
TXS
MR. AMERICA
Ps. I would like to thank my keyboard, my fingers, and me for helping me
writte this bullettin. Wi thout their help I would have never finish this
project.
