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What resistance do I need to change 9 volts from a battery to 5 volts for an atmega328p-pu? Answered

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Hawk-Eagle

4 years ago

Resistors don't decrease voltage, it just decreases the current.

To decrease voltage you need a voltage regulator, i'll give you a very good one with schematic.

Just replace the 78XX in the circuit below with the regultaor you need ( wich will be 7805 ) and you'll be fine.

circuit_regulator_for_78xx.jpg
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seandogueHawk-Eagle

Answer 4 years ago

The source is a 9VDC battery. One diode I guess i could see if I was really worried about connecting in reverse, but a fullwave rectifier is a bit pointless and will simply lead to failure of the circuit far earlier due to battery drain.

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seandogueseandogue

Answer 4 years ago

V1-------R1----(V2)----(some load)----com

V@ will most assuredlyl be lower than V1, unless (some load) is drawing 0 current. Therefore, the voltage decreased, and it did it as a direct result of R1 (a resistance)

Care to comment?

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Hawk-Eagleseandogue

Answer 4 years ago

Sorry for my delay, just I was out of country, and no internet :)

About the diodes, they just convert the AC to DC, you can simply remove them ( as I did ) and every thing will work fine, but you have to leave them if are going to use AC, beside this It's really good and worked for me even with 9V.

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abqlewis

4 years ago

There's no one magic resistance that will drop 9 to 5 volts in a dynamic system containing a micro-controller (328p). For this you would need to change the resistance constantly, dependent on the current draw. etc. This is regulation. Google search "7805", or even more specific, "7805 arduino". While a little more complicated than a current limiting resistor, it's still fairly simple. Also, a good reference for asking about powering an ATMega would be the forums @ avrfreaks.com

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seandogue

4 years ago

You don't. You need a 5V regulator like a 7805 (inefficient but easy to use for the novice).

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Wired_Mistseandogue

Answer 4 years ago

+1, best bet !

This will give you more than enough power for the Micro controller. However, Like Sean said, you may need more power for additional Accessories !