I have designed a SIM900 circuit on a zero pcb board for testing purpose. It is working fine. In my application I need to make a call and then talk to the other person on call. So I have used PIC MCU to initiate a call whenever a person press the switch. The circuit is working as expected. SIM900 requires voltage between
3.3v-4.8v and PIC MCU works on
5V and my input voltage to the pcb is
12v so I have used a
LM317 for SIM900 to give it
4v and have used
LM7805 for PIC MCU to give
When on a call I need to listen to the other person so I have used this speaker but the output audio was very low so I though of designing audio amplifier circuit using
LM386. The circuit is also working fine and giving loud audio. As the input requirement of the LM386 is 5v and because I have designed it on another pcb so I have used the 5v from the
LM7805. I connected everything and pressed the switch. Speakers were making call connecting sound and as soon as the call is connected, there was no sound. I tried again and again and checked the circuit but nothing was wrong. Then I used external 5v power supply and gave it to the
LM386 circuit and now everything started working. There was clear and loud audio. But as I cannot use two different power supplies( 12v, 5v) I need the complete circuit on same 12v supply.
I don't know why its not working on
LM7805 but its working on external power supply. Does anyone have any idea about it. Please help.
Here is the schematic of power circuit:
Below is the schematic of