Baby watch Intercom Circuit

It's a very simple circuit, for the follow-up of baby. It can however be also used for other use, as intercom etc. In the place of M1 we can we use a simple electret mic capsule. The regulation of gain becomes from the R1, whoever can be trimmer or potesometer. Has been added also a small automatism, round the RL1 and battery 9V for the case where we have interruption of AC Line. The life of battery is enough big, one and the consumption of current is small, roughly 30 mA, for loudspeaker 8R /0,4W. The transistors do not need heatsink, one and work in Class B.
Baby watch Intercom Circuit - schematic

Part List R1=15Kohms C1=22uF/25V Q1=BD139 R2-4=1Kohms C2-3-6=100nF/100V MKT Q2=BD140 R3-7=1Kohms C4-9=1uF/25V IC1=TL072 R5=220Kohms C5-8=100pF/100V F1=Fuse 0,1A R6=1Mohms C7-10=470uF/25V P1=470kohms Trimmer or potesiometer R8-9=1Mohms C11=100nF/100V MKT TR1=220Vac/9V 0,2A Transformer R10-11=47ohms C12=1000?F/25V M1=Electret condenset Microphone R12-14=10Kohms D1-5=1N4002 S1=2X2 1A SW R13=1Kohms LD1=Led 3mm RED BATT=9V Battery R15=2.2Kohms RL1=Small RELAY 12V DC

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