5v level shifter

sharpie

Anyone have an opinion about using this to shift 5v signals for use·by a·'propeller newbie'?
http://www.onsemi.com/pub/Collateral/MC74VHC1GT50-D.PDF

I read the thread on 5v inputs etc..· Which didn't confuse the matter, but wasn't quite what I was looking for either...
I just found this as well...· http://www.edn.com/article/CA6335309.html?ref=nbfe
I have·a number of devices (which are 5v serial) I'd like to interface with as little trouble (and as few components) as possible.
I've strayed away from 3v devices until now for this reason....· But I couldn't stay away from the propeller...·



Post Edited (sharpie) : 7/5/2006 10:55:04 AM GMT

Mike Green

The MC74VHC1GT50 looks fine for one way shifting, but may be more than you need most of the time. The EDN article has a number of suggestions that have been mentioned before here. Chip has discussed interfacing with 5V devices and generally suggests using just a series resistor, somewhere between 1K and 10K. I've been using 4.7K resistors for interfacing to servos, PING, IR Buddy, etc. There's a good recommendation for the I2C bus using pullups and an FET in each lead for bidirectional conversion between 3.3V and 5V. It's in the I2C specification from Philips and is references in several places in recent threads in this forum. I'd stick with the recommendations in the EDN article for commercial designs and try 4.7K series resistors for experimentation and prototyping.

sharpie

Sounds reasonable. I had seen the discussions, but was left with a less than easy feeling using a 1K resistor in series.. I was thinking of using the MC74VHC1GT50 for shifting the tx from a 5v device into the propeller, and nothing the other direction since the threshold was low enough the propeller should trigger it.
I may try the 4.7k on another testbed.. As well as the suggestions in the EDN page.

Thanks for the reply!