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Ideas in Red Boxing: Mercury Switches and Brute Force:
By: Cybernetik
January 1992
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Introduction
---------------
Radio Shack's DTMF Dialer (cat # 43-141) can be easily modified
to produce the same frequencies that Pay Phones use for
quarter/nickel/dime signaling back to Ma Bell. This is done by
switching the crystal in the unit from 3.579Mhz To 6.5535 MHz. This
information is completely covered in another file (See 2600
Magazine for details) and will not be covered here.
What I will attempt to cover in this article is 1) A simple way of
modifiying the dialer to switch between DTMF and Red Box Tones,
and 2) A low-cost idea for building the red box from scratch.
Parts Needed
----------------
Ohm Meter
Solder
Soldering Iron
Epoxy or Duco Cement
XT1 6.5535 Mhz Crystal <You should know this by now!>
M1,M2 2 Sub-Micro-Mini Mercury switches
Don't get the ones that radio shack sells. They're WAY
too big. They'll never fit inside the case.
Our goal here is to fit _everything_ inside the case. This box
will function exactly like Count Zero's "Combo Box" <I perfer to
call it a Pink Box, seeing as it combines both the features of
White and Red boxing>
Schematic C R Y S T A L S
---------------- 3.5xx Mhz 6.5535 Mhz
-=-=-=-=- -=-=-=-=-
| | | |
| | | |
M1 \ | M2 \ |
| | | |
O-----------------------------------+-------|-------------+-------+
pads on circuit board | |
where original crystal was removed from | |
O-------------------------------------------+---------------------+
Step-By-Step Construction Details
------------------------------------
** REMOVE ALL BATTERIES BEFORE CONTINUING! **
1> Disassemble the dialer. Remove the 4 screws holding the case
together, and save them. Some prying is necessary to split the
case open, and should be done with the utmost caution. You
_MAY_ desolder the two yellow wires holding the speaker to the
circuit board if you want more room to work in, so long as you
remember where you removed them from. Placement of these two
wires is not crucial. You don't have to remember which wire goes
to what pad, just where you removed them from. (Which will
probably be near the top of the unit)
2> Carefully remove the original crystal from the circuit board.
This will be a small silver cylindrical object, roughly 4 cm long and
.25 cm wide, Soldered horizontally above the battery case, on the
circuit board. Save it!
3> Using an OhmMeter, find out the orientation of the two mecury
switches. Hold the leads to each side of the switch, turning
the switch upside down and right side up until you get a
reading of ZERO on the ohmmeter. This means that you've got a
connection through the switch. Mark an arrow or something on
the switch so that you can remember the orientation.
4) Using Expoy or Duco Cement, Attach the mercury switches, to the
circuit board , so that one's orientation is UP, and the other,
DOWN. When I speak of UP And DOWN, I'm talking about UP and DOWN
in relation to the entire unit. UP means pointing towards the
top, where the three buttons are. Down means pointing towards the
battery case.
This is exteremly important. If you make a mistake, and
have them both in the same direction , the switching action of
the mercury switches will be meaningless.
5) Solder one wire to each leg of the switches. Solder the
other end of these two wires to the bottom pad that you removed
the original crystal from.
6) Solder a wire from the top pad to a leg on the 3.5535MHz Crystal.
7) Solder a wire from the top pad to a leg on the 6.5535MHz Crystal.
8) Solder the remaining leg on the 3.5535 MHz Crystal to the
remaining leg on one of the mercury switches.
9) Solder the remaining leg on the 6.5535 MHz Crystal to the
remaining leg on the other mercury switch.
** ALWAYS REFER TO THE ABOVE SCHEMATIC IF YOU GET CONFUSED! **
TAKE CARE WHEN SOLDERING! THE CIRCUIT BOARD IS WIMPY,
AND COPPER PADS WILL JUST MELT OFF THE BOARD IF GIVEN EXTREME
HEAT!
Reassembly
-----------
10) If necessary, remove the Piezo Speaker (the smaller one) to
make room for the new parts. This speaker is only used during
the programming of the dialer, and you can probably live
without it. Clever people can move this to a different location
within the dialer.
11) Cement the two crystals inside the dialer. Make sure of a few
things: The bodies of the crystals are metal. If you want to
place them in an area with lots of surrounding chips and parts,
place cement down first, then the crystal to prevent shorting.
The expoy can act as a wonderful insulator, and give you much
more freedom as far as parts placement goes.
12) Place the back on the dialer, push it together, and insert the 4
screws again. Tighten.
Testing/Troubleshooting
---------------------------
Turn the dialer on. Insert batteries. Toggle the STORE/DIAL switch
to STORE. Store 1 * in P1, 2 *'s in P2, and 5 *'s to P3.
Return the switch to DIAL.
Press P3. If you hear quarter tones, then you're halfway there.
Turn the unit upside down. Press P3 again. If you're hearing DTMF
tones, You're set.
Depending on how you wired the mercury switches, You may have to
flip the unit around to hear the different tones. I've got the
Red Box tones active when I turn my unit upside down, which I
think is perferred. (It tends to be a bit more discret)...
************
Part Two
************
So, now that you've got a decently looking/functioning Pink Box,
go off and try it. Bone AT&T a few times.
If you're intrested in building a Red Box from scratch, I'll offer
a simple block diagram, and some ideas. I'm not in the mood to
type out a complete schematic for it, but If I recieve enough
requests, then I'll provide complete details.
Insane techincal discussion follows. Ask me questions if you can't
understand me. Don't sit there being confused.
****
A red box can be created with 4-5 chips. You'd need 2 XR2207 VCO's
(Voltage Controlled Oscillator), an LM386 Audio Amplifier, a 556
Timer to do your timings for you, and a 74191 counter chip.
In theory: The duty cycle of the 556 would control the Make/Break
ratio of the tones, acting as a clock. You'd have to adjust this
ratio with either a scope or freq counter, taking a bit of time,
but it'd be worth it. A scope would be preferable, because you
could SEE the timings and adjust accordingly.
The 74191 would be given the output of the 556. Some arrangement of
gates would tell the 74191 when to stop, and you'd switch these
gates, on and off with three switches. It may even be easier to
have three switches controlling the 74191's SET inputs in binary.
(You'd have to hold swithes 3 and 1 to get 5 quarter 'clicks'. Not
too elegant, but functional.)
You'd have to set the two VCO's to the approiate frequency using
potentionmeters. Simple if you've got a freq counter. Also, you'd
have to set the VCO's to function with a sine wave.
This is only a thought. I wouldn't want to go through the trouble of
building this, seeing for $30 you can toss one together via radio
shack...
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Any questiPOk, I was Wrong about fittin that shit in te dialer..
V??R??T.617