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BUILDING A RED BOX
by J.R."Bob" Dobbs
Essentially,the red box is a device used to fool the phone company
into thinking you are depositing coins into a payphone. Every time you
drop a coin into a payphone, the phone signals the type of coin inserted
with one or more bursts of a combination of 1700hz and 2200hz. The tone
bursts are coded as follows:
Nickel:One 60 millisecond pulse
Dime :Two 60 millisecond pulses separated by 60 milliseconds
Quarter:Five 35 millisecond pulses separated by 35 milliseconds
HOW TO USE IT
-------------
Operation is simple. Simply dial a long distance number (some areas
require you to stick in a genuine nickel first), wait for the ACTS
computer to demand your cash, and press the "deposit" button on the red
box for each coin you want to simulate. The coin signals are coupled
from the red box into the phone with a small speaker held to the
mouthpiece. For local calls, either you must first deposit a genuine
nickel before "simulating" more coins or place your call through the
operator with 0 + 7d. Use some care when the operator is on the
line--sometimes they catch on to your beeper ploy.
CIRCUIT OPERATION
-----------------
Each time the pushbutton is pressed, it triggers half of IC1,
configured as a monostable multivibrator to energize the rest of the
circuit for a length of time determined by the setting of the coin
selector switch. This in turn starts the other half of IC1, configured
as an astable multivibrator, pulsing on and off at regular intervals at
a rate determined by the 50k pot between pins 12 and 13. The output of
the astable thus alternately powers of IC2, configured as a square wave
oscillator, providing the required 1700hz and 2200hz to the op amp which
acts as a buffer to drive the speaker.
CONSTRUCTION
------------
Assemble the circuit as you wish. Component placement is not
critical. I found the easiest method was to use point-to-point wiring
on a "universal" PC grid board with solder ringed holes. Use sockets if
you aren't a whiz with a soldering iron. Be sure to leave easy access
to the potentiometers for alignment.
ALIGNMENT AND TESTING
---------------------
For alignment, a frequency counter and tiggered sweep oscilloscope
are extremely handy (but not absolutely necessary.)
Install a temporary jumper from +9v supply to pin 14 of IC2 and
temporarily disconnect the 0.01uF capacitors from pins 5 and 9 of IC2.
Power up the circuit. Measuring the output from pin 5 of IC2 with the
frequency counter, adjust the 20k pot between pins 1 and 6 for an output
of 1700hz. Now adjust the 20k pot between pins 8 and 13 for an output
of 2200hz from pin 9 of IC2. Remove the temporary jumper and re-attach
the capacitors to pins 5 and 9. (Note: if no frequency counter is
available, the outputs can be adjusted by ear one at a time by
zero-beating the output tone with a computer generated tone of known
precision.)
Next, temporarily disconnect the wire between pins 5 and 10 of IC1.
Set coin selector switch in the "N" (nickel) position. With the
oscilloscope measuring the output from pin 9 of IC1, adjust the 50k pot
between pins 12 and 13 of IC1 for output pulses of 60 millisecond
duration. Reconnect the wire between pins 5 and 10. (Note: If no scope
is available, adjust the pulse rate by ear using computer generated
tones for comparison.)
The remaining adjustments are made by ear.
Leave the selector switch in the "N" position. Adjust the 50k pot
labelled "Dime" for a quick double beep each time the pushbutton is
pressed.
Finally, set the selector to "Quarter". Adjust the 50k pot labelled
"Quarter" until exactly 5 very quick beeps are heard for each button
press. Don't worry if the quarter beeps sound shorter and faster than
the nickel and dime ones. They should be.
CONCLUSION
----------
If all went well to this point, your red box should be completely
aligned and functional. A final test should now be conducted from a
payphone using the DATL (dial access test line) coin test. Dial
09591230 and follow the computer instructions using the red box at the
proper prompts. The computer should correctly identify all coins
"simulated" and flag any anomalies. With a little discretion, your red
box should bring you many years of use. Remember, there's no such thing
as spare change.!
Parts list for Red Box
----------------------
Semiconductors
--------------
(2)556 dual timer
(1)741 Op Amp
(1)1N914 Switching Diode
Resistors
---------
(6)10k (1)4.7k
(2)100k
(4)50k PC Mount Potentiometer
(2)20k Multi-Turn Potentiometer
Capacitors
----------
(10)0.01uF (1)1.0uF
(2)10.0uF Electrolytic
Miscellaneous
-------------
(2)14 Pin Dip Socket
(1)8 Pin Dip Socket
(1)3-position Rotary Switch
(1)Momentary Push-Button Switch(normally open)
(1)SPST Toggle Switch
(1)Speaker or Telephone Earpiece Circuit Board
Box
Mounting Hardware
9v Battery Clip
SCHEMATIC DRAWING
-----------------
/
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g ???10 (IC1556) 8??? R6<?? ? R8<??? ? ?
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Speaker
?
g
Schematic part variables list.
------------------------------
Resistors
---------
R1 - 10k R2 - 10k R3 -4.7k R4 - 10k R5 - 10k R6 - 50k
R7 - 50k R8 - 50k R9 - 50k R10- 20k R11- 10k R12- 10k
R13- 20k R14-100k R15-100k
Capacitors
----------
C1 - 0.01uf C2 - 1N914 switching Diode C3 - 1.0uf C4 - 0.01uf
C5 - 0.01uf C6 - 10uf C7 - 0.01uf C8 - 0.01uf C9 - 0.01uf
C10 - 0.01uf C11 - 0.01uf C12 - 0.01uf C13 - 0.01uf C14 - 10uf
Switches
--------
S1 - SPST toggle
S2 - Momentary push button N.O. labeled "Deposit"
S3 - 3-position rotary switch
Miscellaneous
-------------
g - Ground
@q - Label "quarter"
@d - Label "dime"
@n - Label "nickle"