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Author Topic: 5v down to 3.3v for 3.3v sensitive devices  (Read 558 times)
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Just a simple question

If I  am using a 5v arduino and my sensor or device requires 3.3v for power + data lines what is the best way to do this?

Should one just use a voltage divisor with 2 resisters?

Should one use a 3.3v regulator for the power + 2 resisters for the data lines?

Should one use a 3.3 volt regulator for eveything?

Is there something else you should use?

I am just wondering as I have really only used the 3.3v line from Arduino + 2 resisters but is that a good method? Doesn't this waste energy as heat? Especially when running from battery power?

Chris
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You need a regulator for 3.3v, but the Arduino's usually provide that.  You can get by with a resistor divider for data lines in some cases, but a level converter is a better general choice.
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You need a regulator for 3.3v, but the Arduino's usually provide that.  You can get by with a resistor divider for data lines in some cases, but a level converter is a better general choice.

Thanks for the advise, do you have a recommendation on a particular device?

I will do some searches myself now so I can get familar.

Cheers

Chris
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This is a little expensive, but it is a good general purpose converter with eight channels; http://www.adafruit.com/category/products/395


There are many other options though.
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I use this but it looks like they are out of stock.
https://www.sparkfun.com/products/8745
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Quote
You need a regulator for 3.3v, but the Arduino's usually provide that.
Only 50mA, may be enough for an SD card, but not enough for an XBee (for example).
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I did one little breadboard project with a 3.3V GPS device, the only 3.3V device I have interfaced so far.  I did it with an ATMega328P so I didn't have 3.3V from an Arduino.

As for power, I used this regulator which seems to have a good reputation, works fine, multimeter says it is spot on:

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_897188_-1

Now the nice thing is that the GPS could be interfaced to the INPUTs of the ATMega328P fine - 3.3V drives the inputs without any trouble, and the GPS itself needs no input, it starts sending data once it has it.  So I was set there.

If you need to send output to a 3.3V device you need to use a level converter like the one mentioned above which seems to be bidirectional and intelligent and out of stock.  As an alternate, there is this not quite as elegant solution:

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

But it is now out of stock too.  What gives with all these level converters out of stock?

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May be you can did it yourself without waiting for stock.


http://www.rocketnumbernine.com/2009/04/10/5v-33v-bidirectional-level-converter
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Sometimes the better choice can be to run the whole system on 3.3V. Depends on the sensors and other devices involved.

When running on batteries, an Arduino is often not a great choice. For example, an Uno board will consume 3-4 times the current/power of just the ATmega328P microcontroller alone. That is a not criticism; after all, it is a development board, and that is the price paid for the convenience it provides. While the 328P can be put to sleep, and that is a great option for battery-powered applications, certain components on the Arduino board continue to draw power regardless. I would strongly consider a custom circuit design for a battery-powered application.
« Last Edit: August 09, 2012, 07:35:03 pm by Jack Christensen » Logged

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