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Topic: building and arduino breadboard and I need 3.3v (Read 1 time) previous topic - next topic

kelly7552

all,

I followed the directions at http://arduino.cc/en/Main/Standalone and i works great but I need 3.3v.  What would I need to add to get a reliable 3.3V setup for two sensors bmp085 and hhsomethingorother...

thanks,

Bill

robtillaart


AN UNO board has a 3.3 V output, otherwise you need an 7803 (google 7803 3.3V)
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

kelly7552

yeah,

I'm moving from an UNO onto a breadboard.  I already have a 5V voltage regulator on the breadboard, how would I add the  7803?
can I do this with a few capacitors and resistors off the 5V line?

robtillaart

Can be done from the 5V But I would connect the 7803 to your main powersupply (keep them separated)

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

kelly7552

When I used a 5v voltage regulator I used a 10 uF capacitor on the input middle pin and a 10 uF capacitor on the output side between power and ground would I need the same configuration for a 3.3V voltage regulator?

CrossRoads

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM1086IT-3.3-ND

Take a look at the datasheet, page 11, 10uF on input & output.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Grumpy_Mike

Quote
But I would connect the 7803 to your main powersupply

Well I wouldn't, I would connect it to the 5v output of the regulator, that way it has less power to burn off. Also low voltage regulators like this often have a smaller input range.

kelly7552

So Mike,

Connect the 5V as the input to the 3.3V regulator, and use input (between 5V and the middle pin)  and output (crossing 3.3V and ground) 100 uF capacitors?

I'm a newbie....

Bill

CrossRoads

10uF capacitors are all that is needed, 100uF will do fine.
Make sure you get a low dropout voltage 3.3V regulator that can work from 5V. The one I linked for example  needs a minimum of 4.75V.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

rdg123

I just used two resistors as a voltage divider. Are there drawbacks to this method instead of using a regulator?

retrolefty


I just used two resistors as a voltage divider. Are there drawbacks to this method instead of using a regulator?


Yes, the voltage output of the divider can only supply a very small amount of current depending on the size of the resistors and the actual voltage will change if the load changes it's current demand. Voltage dividers should only be used to change signal voltage levels, not to provide power to a component, that requires a constant voltage regulator.

Lefty

CrossRoads

'Course, if you know how much current you will be drawing, you can set  your voltage to be at 3.3V for that one specific current.
Is not a reliable way to go tho as Lefty said.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Grumpy_Mike

The general rule is to have the current down the potential divider to be ten time the current you want to draw.

Powering stuff with a potential divider is total and absolute rubbish.

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