While procrastinating on solving the software issues around the ADC, I've been working on a PCB layout. I finally finished the layout tonight, and ordered some PCBs from JLCPCB.

Here's hoping it all works!

The board has:

• Breakout of most of the ESP32-WROVER module's pins
• A cutout where the Baofeng's belt clip can sit and keep the board in place.
• A header meant to interface with the wESP32-Prog module (to help minimize the number of components)
• A DC-DC power supply based around the XL1509 (the cheapest non-inverting DC-DC converter IC available as a "basic part" from JLCPCB).
• The audio components
  • a clamp circuit that lets us get an interrupt when the audio input goes high without blowing out the GPIO pin.
  • a 4:1 voltage divider to drop the Baofeng's 0-8.4V audio output down to a range tolerable by the ESP32's ADC
  • A voltage divider / RC filter / DC blocking capacitor for smoothing the DAC output and dropping it to a level that the Baofeng's microphone input can handle.

The clamp circuit on the PCB is different than what I've prototyped (it uses a 3-terminal voltage reference instead of 2 red LEDs), and my prototypes have been using DC-DC modules from aliexpress, so if I made a mistake it's likely in one of those two places.

For the DC-DC converter, I was going to use the same IC as these aliexpress modules, the MP2315, but that's an "extended component", and I balked at paying an extra $3. That may have been a mistake in hindsight -- the XL1509 has higher quiescent current and lower efficiency than the MP2315, which may end up negating the benefits of using a DC-DC converter instead of a simpler linear voltage regulator. I only noticed this after placing my order.

Assuming this works & doesn't require too many more components, I'm pretty happy with the result. In small quantities (5pcs), these boards cost $8 each for manufacture/assembly/shipping. JLCPCB doesn't stock any ESP32 modules or do through-hole assembly, so 0.1" header pins + the ESP32 module + the pogo pins I'm using as battery contacts still need to be added, which should be less than $5 per board.

This is my first PCB layout, so I'd love to hear any feedback you have on the design.