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### Topic: 3.3 volt I/O pins (Read 2051 times)previous topic - next topic

#### Macnerd

##### Jun 14, 2014, 04:23 pm
If one needs more than 3.3 volts to drive some external device, what does one do? I suppose that some hardware has to be between the Due & the device to be powered. How is the voltage increased?

#### vffgaston

#1
##### Jun 14, 2014, 08:57 pm
Quote
If one needs more than 3.3 volts to drive some external device, what does one do? I suppose that some hardware has to be between the Due & the device to be powered. How is the voltage increased?

You have two concerns:

1) The voltage you need (for the "other thing" you have to supply -i.e.: motor, display, . . . .).

2) The power -wattage- it needs.

There are some devices that allow you to have higher (or lower) voltages from the 3.3 V that supply the arduino ( By the way: what is your "primary" 3.3 V source -USB, batteries, . . .?) but limited to the power that this primary source is able to supply.

It all is becaming a mess: what is your project?

Regards.

#### Macnerd

#2
##### Jun 15, 2014, 09:42 pmLast Edit: Jun 15, 2014, 09:50 pm by Macnerd Reason: 1
I haven't bought the Due yet, but 3.3 volts is not a common voltage. A lot of ICs run off of 5 volts. I googled 3.3v to 5v convertor & read about a logic shifter.

"There are some devices that allow you to have higher (or lower) voltages from the 3.3 V that supply the Arduino ( By the way: what is your "primary" 3.3 V source -USB, batteries, . . .?) but limited to the power that this primary source is able to supply."

I have a wall-wart that has an output of 12V at 300 mA. I measured the outside diameter of the plug & it's about .25 inches. I can use that, can't I?

I'm primarily interested in experimenting with RGB LEDs & the 3.3V output is within the range of voltages for the RGB LED. But, I'll probably want to experiment with ICs or whatever that require a higher input voltage than 3.3V. That's why I'm wondering how I can get a higher voltage than 3.3 volts to power components that need more than 3.3V. This convertor would go between the Arduino & the component. So, somehow, the input is 3.3V & the output is whatever.

#### MarkT

#3
##### Jun 16, 2014, 12:17 pm

I haven't bought the Due yet, but 3.3 volts is not a common voltage. A lot of ICs run off of 5 volts. I googled 3.3v to 5v convertor & read about a logic shifter.

Its a very common voltage.  In fact nearly all new logic chips support it.  5V is becoming
"legacy".  Most Arduinos use chips that can run between 1.8 and 5V, although most
are actually used at 5V.  Many sensors are 3.3 and 5V compatible and many are 1.8 to 3.6V
only nowadays.  All mobile phones use 3.3 as the bus voltage these days so that all the
new chips destined for phones (like gyros, accelerometers, light sensors, magnetometers,
etc etc) are 3.3V compatible, and of course SD and microSD cards are 3.3V or below.

I'm talking about chips released in the last decade of course, not prehistory

BTW its "level shifter", not "logic shifter".  These are readily available on breakout
boards and many simple circuits can perform the same function.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### Macnerd

#4
##### Jun 16, 2014, 04:19 pm
I wasn't aware that there are new ICs that run on 3.3V. Has the "name" changed? Are there still 7400 series, etc. chips? How would I know if a "new" IC runs on 3.3V? What do I look for? I've googled level shifters & they require both 3.3V AND 5V.

I have a wall-wart that has an output of 12V at 300mA. I measured the outside diameter of the plug. It is .25 inches. Can I use that to supply the DC?

I know that I can set the pins as output or input. If I wanted to Charlieplex, it would be easy to switch the pins back & forth. Can I set the output pins as binary-weighted pins? Let's say that I convert a decimal value to a binary value in software. I want to have each output pin a different binary value. I want the "1" output on a certain pin & the "2" output on a different pin & the "4" output on a separate pin. So, an octal value of 101 would be output on the 1st pin, 2nd pin & 3rd pin. Is that even possible? The reason why I'm wondering is because RGB LEDs have 3 color pins. As you know, 2 raised to the 3rd power is 8. If that is possible, the software can create random binary numbers between 0 & 111 & output the values to the "binary" pins.

#### CuriousPanda

#5
##### Jul 31, 2014, 06:46 am
Hi,

I am using an arduino Due to communicate with sensor that uses SDI12 protocol.
I have found SDI12 library for Arduino on github.
However, because SDI12 low and high voltage ranges between 0-5V, how should I connect it with the due?

Thanks.

#### MarkT

#6
##### Jul 31, 2014, 07:56 pm
Quote
I wasn't aware that there are new ICs that run on 3.3V. Has the "name" changed? Are there still 7400 series, etc. chips? How would I know if a "new" IC runs on 3.3V? What do I look for? I've googled level shifters & they require both 3.3V AND 5V.

You need to find a good comparison of logic families.

Start here but stop every so often to eat and drink!

http://en.wikipedia.org/wiki/Logic_family
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### bobcousins

#7
##### Jul 31, 2014, 08:12 pm

Hi,

I am using an arduino Due to communicate with sensor that uses SDI12 protocol.
I have found SDI12 library for Arduino on github.
However, because SDI12 low and high voltage ranges between 0-5V, how should I connect it with the due?

Thanks.

Well, Firefox just lost my reply, so here goes again:

Unfortunately, SDI signal levels are not compatible with 3.3V, which is a shame because otherwise it is a simple protocol.
You will need a circuit to do some bidirectional level shifting e.g. http://www.daycounter.com/Circuits/SDI-12/SDI-12-Interface.phtml

You may need to make some changes to the SDI libray to toggle the direction control.

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