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random thoughts about nonrandom things

Hairy Circuit Layout Issues

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Posted
By dragoncoder047
Tags: electronics

This post is part 3 of the roboraptor-upgrade series:

  1. Shifting Gears
  2. Systems Tested
  3. Hairy Circuit Layout Issues
  4. Well, I Got Something...
  5. Not Your Daddy's Boost Converter
  6. Error: out of memory

I’m starting to finalize the circuit boards needed for my Roboraptor upgrade. I am doing everything with THT components, which take up a lot of space, but I can solder by hand easily. Unfortunately, this means everything takes up a lot of space.

The top board, which will go in the same spot as the original board, is limited to about 2 inches by 3 inches of board area and not a lot of vertical space. Fortunately there are a bunch of spaces in the rest of the Roboraptor’s structure that I can squeeze a small co-processor circuit board to run a few motors. But there isn’t really anywhere else I can put the amplifiers for the audio system.

The electret microphones’ preamplifier is a LM358, fixed with resistors to give a gain of +20dB (if I did the math right; it’s an arithmetic gain of 100), and conveniently the LM358 is a dual op-amp so I only need one chip for the two microphones.

LM358 preamp

I was running low on pins coming out of the ESP32, so I ditched the MAX98357A (which requires 3 pins for the I2S bus) in favor of a simple one-pin solution: use the ESP32’s internal DAC. This requires an amplifier, so I turned to the trusty LM386.

LM386 amplifier

So far, here’s what I need to put on the top:

Whew, that’s a lot… and that’s only one board out of probably, like 5 of them… I have some serious work to do!

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