simple 3.3v / 5v level conversion solution

[bobf]

One simple solution for level conversion involves a CD4050 hex non-inverting buffer.  This particular device allows the input voltage to exceed the power supply voltage, and the output will be limited by the power supply voltage.

I have (in the past) successfully used this particular device to convert 5V outputs from an Arduino Uno 'compatible' device to a 3.3v device that was (according to the spec sheets) NOT 5V tolerant on its inputs.  The arduino WILL accept 3.3v logic levels, though.  So there was no need to perform any level conversion going back the other way.

In short, you power the CD4050 with whatever logic voltage level you want.  In my case that was a 3.3v regulated power supply.  Then you connect the 5V logic to the input of one of the gates, and the output of the gate to the 3.3v logic.  The CD4050 can drive 2 TTL gates from any of its outputs, so there's no problem connecting to any device that I'm aware of.

CD4050 digikey part  (16-pin DIP; also available as surface mount)

[Glen Johnson]

Thanks for the info.

 

Sparkfun makes something similar,

https://www.sparkfun.com/products/8745

but this CD4050 costs less.

 

[bobf]

On Thursday, January 10, 2013 9:57:28 AM UTC-8, Glen Johnson wrote:

Sparkfun makes something similar,

https://www.sparkfun.com/products/8745

but this CD4050 costs less.

 
Thanks for the mention.  I took a close look at that board, and although it might be a nice reliable bi-directional solution, it ALSO has 10 SMT parts on it (from the photo), so when it comes time to make a final design out of it, that's a lot of additional parts (vs a single IC).  Still nice to see the sparkfun board, which is relatively cheap, so thanks for adding that to the thread.  It's also bi-directional for cases where the 5V side can't tolerate 3.3v logic levels.  Also, for a lot of experimenters, the Sparkfun might be easier to work with.

[dama...@gmail.com]

If I connect 5v to pin 1 (Vcc) and Gnd to pin 8 (Vss) I get 4.8V in the output of a 5V input. But is strange, if I left pin 1 unconnected y get an output of (3.3V) from a 5v input. Any explanation? I need this behaviour of 5v to 3.3v working, but i am concerned about leaving pin 1 unconnected

[dama...@gmail.com]

> If I connect 5v to pin 1 (Vcc) and Gnd to pin 8 (Vss) I get 4.8V in the output of a 5V input. But is strange, if I left pin 1 unconnected y get an output of (3.3V) from a 5v input. Any explanation? I need this behaviour of 5v to 3.3v working, but i am concerned about leaving pin 1 unconnected

Connecting 3.3V to the pin 1 have the same effect. I get 4.8V in any output