3.3V from 5V

Development Boards Arduino
1

I need to use an SD card shield with a Pro 5V board. I was under the impression that the Pro 5V had the same pinouts as the Arduino Uno, but I was mistaken. It appears that the pin on the Pro that matches up to the pin on the Uno that puts out 3.3V actually puts out 5V.

What’s the best way to reduce 5V down to 3.3V? I’m thinking resistor, but I’d need to know the exact current draw of the SD shield to calculate that. I thought of going with a 3.3V board, but that would be even more work considering I need 5V discrete logic out and have 5V going in from another circuit.

Thanks

2

i’m curious of the ‘best’ method. If you have only a few lines needing to be lowered and current draw is virtually nothing, use a resistive divider.

http://en.wikipedia.org/wiki/Voltage_divider

resistive divider

reminds me of the OLED screen from adafruit needs 3.3v, so using a level shifter:

http://www.ladyada.net/images/oled12864/chipwire2_t.jpg

just check everything with a voltmeter before connecting

3

Just use a 3.3 V LDO regulator.

4

leon_heller:
Just use a 3.3 V LDO regulator.

Thanks…Don’t know why I didn’t think of that. I use the 5V version of this all the time.

5

I’ve used two silicon diodes in series. Close enough, in many cases.

Mind the current rating.