schematic for sim300 is this OK

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#1
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i am making this circuit, the speaker and mic outputs are going to be amplified externally. so i am connecting them directly to RCA ports, i have almost no experience for audio circuits, so please check this schematic and give me some advice. the power supply section is OK i have tested it although its with minimum parts. the output is 4.18 volts.

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i will post my complete pdf that has a atmega644 interfaced with this sim300 ... it has extra components such as two relays and a rs485 interface. please the sim300 hardware conncetions if its ok .

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I only see one capacitor on the Vcc line (C3).

Ross McKenzie ValuSoft Melbourne Australia

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I'd also suggest a pulldown resistor on the enable to the 485 driver to ensure it doesn't go into transmit when the micro is reset.

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The manufacturer recommends a 100uf low ESR capacitor from the VBAT pins to ground, placed as close to the sim300 as possible. Either use a bunch of multi-layer ceramic capacitors to get the 100uF, or else a 100uF tantalum capacitor with a 10uF ceramic capacitor in parallel with it. I'd also place a 100nF ceramic capacitor from every single power supply pin to ground on all the other chips, again, placing the capacitor as close to the pin as possible.
I also see a couple of AGND pins on the sim300 that are not connected. I'm pretty sure those should go to ground somewhere, check the specifications for the sim300