Question for you 3.3v proc users

Community General Discussions
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1

Heya fellow lmr folks.

So I've been using procs that are 5v powered and sensors that align with that voltage as well so I have a nice collection of various devices that I can use in this power range. Since I'll be working on a project based on the xmos chip I noticed that it's a 3.3v chip...and my problem currently is I'm not familiar with using 5v devices with the 3v procs. I've searched google and found some info, but wondered if anyone else had resources for doing this. I want to be sure I cover my bases and don't fry the board on the first try. releasing magic smoke! DOES NOT WANT!!!

I've also found things like the need to use a a special chip or board for digital signals and for analogue I could use something like the following.

 

Basically what I'm looking for are words of wisdom from the folks who have delved into this area and what they've found works well, and what doesn't work well.

Any insight/info is welcome!

Thanks!

 

 

2

There is 5 volt tolerant and

There is 5 volt tolerant and not 5 volt tolerant stuff. Freescale DSP56F803 micros were 5 volt tolerant and worked with 5 volt devices fine, no worries. XBee radios were not tolerant and would fry if hooked to 5 volt TTL, at least older versions did.

Various adjustments can be made, from resistors to buffer or inverter chips that have 5 volts on one side and 3.3 on the other. 74AC05 hex inverter, 74LCX245 bidirectional transciever.

Most 5 volt TTL will read 3.3 volt signals fine. Have not run into an RC servo that will not operate from a 3.3 volt servo pulse.

3

I am using the Propeller and it is a 3.3V chip

Since the Propeller is 3.3V and many other sensors and attachments are 5V like I2C etc.

This subject was discussed quite thoroughly here at this Parallax Thread with examples that could give you some ideas how to interface your chip safely. Hope this helps.

4

It seems the XS1-G has 5v
It seems the XS1-G has 5v tolerant input pins according to this document on IO connecting but I couldn`t find any mention of the other chips.

5

Thanks Grue, this will

Thanks Grue, this will actually be very helpful.

and I was hoping you’d chime in as i know you’ve been working with the prop!!

Thanks again! :smiley:

6

yeah, I haven’t found much

yeah, I haven’t found much info on voltage tolerance in the documentation I’ve looked at…I was hoping to find a bit more but ah well.

I’ll take a look at the xmos forums this weekend and see if I can find any info.

7

You are welcome

I built my own 5V to 3.3V interface board since my HB-25’s and sensors are 5V.

Tobi_1_Pics_152.jpg

It has its own 5V regulator and gives me GND/5V/Signal on the center three rows of pins and my 3.3V Propeller plugs into the last row on the outside. This perfect for plugging in Servos, RF Reciever, PING)))'s and my Serial LCD. I even added the Blue connector at the bottom of the picture so that I could daisy chain another board off of the single 5V regulator