Programmable Dial-Out BlockingDevice
barring premium rate numbers
Published in issue 316, December 2002
Premium rate numbers (in the UK, generally those starting with 09) are often used as a way of extracting payments from telephone users and Internet surfers. This is however illegal if it is done covertly without the knowledge of the user. The circuit described here blocks such numbers and cannot be defeated.Despite the best endeavours of consumer protection organisations there is still much abuse of premium rate telephone numbers. In particular, it can happen that while surfing the Internet, unbeknown to the user, a new dialler program is downloaded which terminates the call in progress and dials out again on an expensive premium rate number. Unfortunately dialler guard programs are no defence against such underhand activity, since as soon as some new piece of protection software appears it only takes the hackers a short while to develop a way to get around its security.
Resistors:
R1,R3,R4 = 100kΩ
R2,R9 = 1kΩ
R5 = 270kΩ
R6 = 47kΩ
R7 = 56kΩ
R8 = 10kΩ
Capacitors:
C1,C4 = 10nF
C2,C9,C10,C16,C17 = 100nF
C3 = 4µF7 16V radial
C5-C8,C11,C14 = 10µF 63V radial
C12 = 100µF 25V radial
C13,C15 = 27pF
Inductors:
L1,L2 = 2-hole ferrite core, 2 x 2 turns ECW
Semiconductors:
D1,D4 = 1N4001
D2 = LED, green, high efficiency
D3 = LED, red, high efficiency
T1 = BC547B
IC1 = EEPROM, 24C02 or larger, in DIL8 case
IC2 = AT89C2051, programmed, order
code 020106-41
IC3 = MAX232CP
IC4 = MT8870 or KT3170
IC5 = 7805
Miscellananeous:
K1,K4 = 6-way RJ45- or RJ11 socket, PCB mount
K2 = 9-way sub-D socket (female), angled pins, PCB mount
K3 = mains adaptor socket
S1 = pushbutton, 1 make contact
X1 = 3.579545MHz (NTSC) quartz crystal (32pF parallel resonance)
Re1 = 12V relay, 2 changeover contacts, Fujitsu D012-02CP or Siemens V23042-A2003-B101
X2 = 11.0592MHz quartz crystal (32pF parallel resonance)
Re2 = NP-CL-1A181-4/4-218 (Meder/Finder/Omron) supplied by ELV (www.elv.de)
PCB, order code 020106-1
Disk, project software, order code 020106-11
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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