Saturday, August 07, 2010

Voltage dividers for 5volt Arduino and 3.3volt SPI devices

I am setting up a radio module to plug into an Arduino.
Specifically the RFM12B like in this schematic;

The Arduino runs at 5volts and the RFM12B runs at 3.3volts. So I have to convert the line levels from 5v -> 3.3v on the inputs to the SPI device and from 3.3v -> 5v for the output.

The example has a 4K ohms and a 10K ohms resistor for the 5v to 3.3v voltage dividers for the Arduino output data lines into the RFM12B, does that sound reasonable?

I did the math and worked through the examples on the Arduino tutorial site and came up with the following values; 1.5K ohms, 2.2K ohms

72, Kim