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How to build a BLUE BOX
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We all know that the touch tone frequencies are composed of 2 tones (2
different frequencies) so that is the reason why we have 2 VCO's (Voltage
Controlled Oscilators). We will call then VCO#1 and VCO#2. If you have
noticed VCO#1 and VCO#2 are exactly the same type of circuits. That is why
only 1 was drawn. But remember that whatever goes for VCO#1 also goes for
VCO#2. Both VCO'S are composed of a handfull of part. One chip, two
capacitors, 2 resistors and five potentiometers. All of this will give you
(when properly calibrated) one of the freqencies necessary (the other one
will come from VCO#2) for the operation of the Blue Box. Both of these freqs.
will be mixed in the speaker to form the required tone.
This is one of the most sophisticated designs I have ever made. Why?
Because other designs will drain the battery after 10 calls. This design will
make them last 10 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 calibrate the unit
before we get to the keyboard construction.
VCO CONSTRUCTION:
----------------
TOOLS REQUIRED
1 ocilliscope(optional but not req)
1 Freq. counter (REQUIRED)
1 Volt meter " " "
Electronics tools (Pliers,drll,
screwdrivers, etc.)
=====================================
PARTS
R1 1.5K RESISTOR 5%
R2 1K RESISTOR 5%
C1 .1uf ELECTROLYTIC CAPACITOR 16VDC
C2 .01uf " " (MYLQR)16VDC
IC1 2207 VCO CHIP BY EXAR ELECTRONICS
Remember the above only says
VCO#1 but the same is 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) &
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 DIODE
THAT IS CONNECTED ACCROSS IT.
=======================================
IMPORTANT NOTES
1. DO NOT USE ANYTHING ELSE OTHER
THAN A MYLAR CAPACITOR FOR C2.
2. PINS 10,9,8 SHOULD BE TIED
TOGETHER AND BE LEFT FLOATING.
3. ALL RESISTORS 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 pleases you. Check for cold solder joints, broken wires,
polarity of the battery, etc. Before we apply power to the VCO'S we have 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 lead of your volt meter on pin 7 and the negative
lead on pin 12. If you do not have anything there turn off the unit and
RECHECK THE WIRING.
When you get the right voltages on the chips, 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 labeled
T1-T10 for all pots). You should be able to hear a tone, if not disconnect
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 are dead. So in this case it is always good
to have an ocilloscope on hand. Disconnect the speaker from the circuit and
hook the ocilliscope to 1 of the leads of the speaker & the ground from the
scope to the ground of the battery. Connect again the ground lead with the
diode connected to it from ground to any pot on the VCO that you are checking
and you should see a triangle wave if not turn the pot in which you are
applying 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. (amplitude is about 2VAC). When
you get the two VCO's working you are set for the adjustment of the
individuals pots.
Adjustment
----------
Disconnect the speaker from the circuit and connect a freq. counter (the
positive lead of the counter to one of the speakers leads that belongs to
VCO#1 or connect it to pin 14).
Connect the negative lead to the battery negative and connect the jumper
lead with the diode from 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 differents freqs. which are:
$$$$$$$
$ P1= 1700hz $
$ P2= 1300hz $
$ P3= 1100hz $
$ P4= 900hz $
$ P5= 1500hz $
$$$$$$$
Now disconnect the freq. counter from the speaker lead of VCO#1 or from
pin 14 (which ever you had it attached to at the beginning) and connect it
to the speaker lead of VCO#2 or to pin 14 of VCO#2 and make the same
adjustments to P6-10.
$$$$$$$$
$ P6= 1100hz $
$ P7= 700hz $
$ P8= 900hz $
$ P9= 2600hz $
$ P10= 1500hz $
$$$$$$$$
When you finish doing all of the pots go back and re-check them.
Keyboard
--------
If you look at FIG-2 you will see that the keys are simple switches.
Connected to a ground and two diodes on the other end. these diodes are used
to simplify the construction of the keyboard because otherwise the
distribution of the ground signal for both VCO'S would have been done
mechanically. The diode will go to VCO#1 and the other will go to VCO#2.
FIG-3 shows the arrangement of the keys on the keyboard.
Below is a table that will help you connect the keys to the required VCO's
pots.
(-FIG 2-)
-----!-----!--------!--------!-------
! ! ! !
TO ! TO ! FREQ ! FREQ ! KEY
POT ! POT ! OUT: ! OUT: !
ON ! ON ! ! !
VCO1! VCO2! ! !
-----!-----!--------!-------%!-------
1 ! 06 ! 1700hz ! 1100hz ! C
2 ! 10 ! 1300hz ! 1500hz ! 0
1 ! 10 ! 1700hz ! 1100hz ! E
4 ! 07 ! 0900hz ! 0700hz ! 1
3 ! 07 ! 1100hz ! 0700hz ! 2
3 ! 08 ! 1100hz ! 0900hz ! 3
2 ! 07 ! 1300hz ! 0700hz ! 4
2 ! 08 ! 1300hz ! 0900hz ! 5
2 ! 06 ! 1300hz ! 1100hz ! 6
5 ! 07 ! 1500hz ! 0700hz ! 7
5 ! 08 ! 1500hz ! 0900hz ! 8
5 ! 06 ! 1500hz ! 1100hz ! 9
- ! 09 ! ------ ! 2600hz ! X
Remember that in FIG-2 it's the same for each key except the "X" key,
which only takes one diode.
few KEYS to the diagram:
Cx is capacitor #x Denoted by: ---| |
---
Px is Pot or Variable resistor #x Deno
ted by :/
\
/<--
\
Rx is resistor #x Denoted by /\/\/\/\
SCHEMATICS
The XR-2207 chip is a Voltage-Controlled Oscillator and a 14 pin device
thus you must be very careful when soldering the parts to this device. It is
a little dificult to actually draw a schematic on an 80 character screen
using limited graphics, but I will give
it a try.
TO GND_____________
|
___
C2 C3 ___
_||_ |
| | _____|__9v+
| | | |
` ` ` ` ` ` ` |
------------------------------- |
7 6 5 4 3 2 1 | |
| < |
|8 9 10 11 12 13 14| |
------------------------------- |
` ` ` ` ` ` ` |
| | |
--| |--------| | |
|C1 R2 | R1 |
GND ______|___/\/\/\/\______|_____/\/\/\/\______|
is is a diagram of how to locate the different pins on the chip.
Please notice that pin one (1) is the closest to the notch on top of the
chip. The first thing we'll do is to connect power to the chip (remember that
you need to build two (2) of these to get a complete system) this is
accomplished by connecting the positive wire of the battery lead to pin#1 one
leg of R1 and R2 is soldered to pin#11. The other leg of R1 goes to pin 1
or to the d. C1 goes between pin 10 and ground. The timing capacitor or C2
goes between pins 2 and 3 of the chip. Pins 8 and 9 should be grounded to
ground. Pin 14 is the output and this is where one leg of C4 (C3 goes on the
other VCO) in series with R3 (the same goes for the other VCO) and to one
lead of the speaker.
The trimmer pots P1 to P10 should be grouped in groups of 5 pots each.
The way you group it is by soldering one end of the pot to each other leaving
the wiper and the other end free.
| This end goes to pin 6 of the chip
|
_____________|_____________
/ / / / /
\ \ \ \ \
/<- /<- /<- /<- /<-
\ | \ | \ | \ | \ |
/ | / | / | / | / |
| | | | |
| | | | |
P1 P2 P3 P4 P5
And finally this is the way each key should be wired.
diode
he contact of the
|--------- \------ key
to Px ------>|-----| |
diode |
-----
--- Ground