Resistors:
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
Capacitors:
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
Semiconductors:
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
Miscellaneous:
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