Raspberry Pi Serial Console With MAX3232CPE

In addition to the audio, video, network and USB connectors, the Raspberry Pi also has 26 GPIO pins. These pins also include an UART serial console, which can be used to log in to the Pi, and many other things. However, normal UART device communicate with -12V (logical “1”) and +12V (logical “0”), which may just fry something in the 3.3V Pi. Even “TTL level” serial at 5V runs the same risk.

So in this short tutorial, I’ll show you how to use a MAX3232CPE transceiver to safely convert the normal UART voltage levels to 3.3V accepted by Raspberry Pi, and connect to the Pi using Putty. This is what you’ll need:

  • Raspberry Pi unit
  • Serial port in your PC or USB to serial -adapter
  • MAX3232CPE or similar RS-232 to 3.3V logic level transceiver
  • 5 x 0.1 uF capacitors (I used plastic ones)
  • Jumper wires and breadboard
  • Some type of female-female adapter

The last item is needed to connect male-male jumper wires to RaspPi GPIO pins. I had a short 2×6 pin extension cable available and used that, but an IDE cable and other types ribbon cable work fine as well. Just make sure it doesn’t internally short any of the connections – use a multimeter if in doubt!

The connections on Pi side are rather straightforward. We’ll use the 3.3V pin for power – the draw should not exceed 50 mA, but this should not be an issue, since MAX3232CPE draws less than 1 mA and the capacitors are rather small. GND is also needed, and the two UART pins, TXD and RXD.
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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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