3.3V UART with MAX3232CPE

Before diving right into SPI communications for my SD tutorial, I wanted to have a 3.3V development platform that could output some meaningful status information, not just light a LED if something goes wrong. In this post, I will outline the basic testing platform that will be used in the upcoming part 3 of that tutorial, and discuss a little about UART on AVR in the progress. Here’s what we’ll build:

If you want to build it yourself, you’ll need:

  • ATtiny2313 or other AVR chip with UART pins (RX/TX) separate from SPI pins (MOSI/MISO/SCK)
  • 20 MHz crystal (other speeds will work, too) and ~27 pF capacitors
  • 4k7 pullup resistor for ATtiny2313 RESET pin
  • 3.3V regulator such as LD1086V33 or some other 3.3V voltage source
  • 2 filtering caps for the regulator input/output sides, 10 uF
  • MAX3232CPE or similar RS-232 transceiver that works on a 3.3V voltage
  • RS-232 port on your computer or a USB to RS-232 dongle
  • RS-232 to breadboard connector (home-soldered example seen above)

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