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I have designed a schematic for a PCB for a doppler sonar project. The plan is to use a RPi 3B+ for some basic signal processing, an arduino to produce a 40 kHz wave via PWM which is filtered to produce a 40 kHz sinusoid, which is transmitted after a Tx circuit, and then received through an Rx circuit, sampled with an MCP3008 to the arduino, which will send data to the Pi. Im using 2 x LiPo batteries in parallel to power it, and have a battery charging circuit included, to charge them in parallel. I've used a nMOS to switch off the main circuit when the batteries charge (when USB is plugged in, circuit is off).

With that context, are there any glaring issues with the schematic that I should address before making the PCB? Specifically the RPi powering circuit and the circuit turn off while charging circuit? This project is purely for fun and learning purposes. See images attached (in the order they appear: Overall circuit, RPi powering circuitry, circuit turn off when charging, battery charging circuit).

Schematic overview RPi powering Circuit turn off when charging

Battery charging circuit

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  • \$\begingroup\$ How are you interfacing the transmitter & receiver to the transducer? Do you need a time variable gain amplifier for the receiver to deal with path attenuation (depends on number of A/D bits and if you want this to work over large distances, or not)? For readability of your schematic, please use standard op-amp symbols instead of boxes. \$\endgroup\$
    – qrk
    Mar 3 at 20:13
  • \$\begingroup\$ Transmitter and receiver pins will have jumpers to connect to 2 through-hole 40 kHz barrel transducers. Large distances aren't a huge concern - I've tested a stripboard design of the sonar project. This is more an exercise to make it standalone instead of PC-based as it was, and to make a PCB. Thanks for the tip regarding op-amp symbols, thats a good point. \$\endgroup\$ Mar 3 at 20:30

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