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Remote Control by Mobile Phone

Switch & control using DTMF signaling

Remote Control by Mobile Phone
Many of you will have an old mobile phone gathering dust. The circuit shown in this article gives the old mobile a new lease of life, enabling it to switch an electrical appliance on and off in or around the home. The circuit will even talk to you on in reply to predefined commands.
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Component list
R1 = 390k
R2 = 1k
R3,R5,R12,R15,R17-R23 = 10k
R4 = 100k
R6-R10 = 33k
R11 = 470k
R13 = 220k
R14 = 47k
R16 =2k2
P1 = 1M preset H
P2 = 25k preset H
C1,C3,C6,C7,C15,C17-C20 = 100nF
C2,C13 = 1µF 16V radial
C4,C5 = 27pF
C8 = 2µF2 16V radial
C9,C10 = 220nF
C11,C14 = 22µF 16V radial
C12,C16 = 10µF 16V radial
C21 = 1nF
D1,D2 = 1N4001
T1,T2 = BC547B
IC1 = MT8870BE
IC2 = PIC16F84A-20/P (programmed, Publishers’ order code 040415-41*)
IC3 = ISD25120P (Winbond, Digikey # ISD25120P-ND)
IC4 = 7805CP
K1 = 4-way SIL pinheader
LS1 = 16 Ohm miniature loudspeaker
MIC1 = electret microphone capsule
S1,S2 = pushbutton, 1 make contact
S3-S7 = on/off switch, 1 make contact
X1 = 3.579MHz quartz crystal
Mobile phone with headset (see text)
PCB, Publishers’ order code 040415-1*
PIC source and hex code files, Publishers’ code 040415-11
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