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DTMF Remote Telephone Switch

DTMF Remote Telephone Switch
In spite of alternatives based around the Internet, SMS and e-mail, the good old DTMF remote switch still has its place, and, thanks to the use of a modern microcontroller, is simple and economical.Today a telephone connection is available anywhere and at any time, with forms of communication other than speech having been available for some time. Alongside SMS and WAP there is the simpler established technology, known as ‘Dual Tone Multi Frequency’, or DTMF for short, which we use here in order to control a circuit. Telephone service providers have used this dialling system in the analogue telephone network to replace pulse dialling, which dates from days of mechanical uniselectors. Once a telephone connection is in place, a transmitted tone can be used in order to trigger a desired action.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1,R3 = 270?
R2 = S07K130 (130V varistor)
R4,R5 = 4k?7
R6,R7,R8 = 10k?
R9 = 2k?2
R10,R11,R13,R14 = 100k?
R12 = 270k?
R15 = 1k?
R16,R17,R18 = 180?
P1 = 470k? (500k?) preset
C1 = 470nF 100V MKT, lead pitch 5mm
C2 = 1µF 63V axial
C3,C4,C5,C7,C10,C11 = 100nF, lead pitch 5mm
C6,C8 = 47µF 25V axial
C9 = 470µF 40V axial
B1 = B40C800, round case (80V piv, 0.8A)
D1-D8 = 1N4004
D9 = LED, low current, red, 3mm
D10,D11,D12 = LED, green, 3mm
IC1,IC5,IC6,IC7 = CNY17-3
IC2 = MT8870DE
IC3 = PIC16F84A-20/P, programmed, order code 020294-41
IC4 = 7805
T1,T2,T3 = BC639
JP1 = 2-way pinheader with jumper
K1,K2,K3 = RJ11, PCB mount
K4,K5,K6,K7 = 2-way PCB termibal block, lead pitch 5mm
S1 = pushbutton, 1 make contact, chassis mount
X1 = 3.579545MHz quartz crystal
X2 = 4MHz 3-pin ceramic resonator
Optional: 24-way SIL pinheader with 6 jumpers
PCB, order code 020294-1
Disk, project software, order code 020294-11 or Free Download
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