# Problem powering circuit through 9V battery + Voltage Regulator

I have a circuit that has a Atmega328p running on 5V and a transceiver that runs on 3.3V.

I tried plugging a 9V battery into a LD33V voltage regulator to power the transceiver but it didn't work. I tried different regulators and different batteries, nothing worked. So instead I plugged the transceiver into the 3.3V pin on my Arduino Uno board and powered the Arduino Uno board by plugging the same 9V battery into the barrel jack. It worked perfectly fine then.

This is the type of voltage regulator that I am using: https://www.sparkfun.com/products/526

Any ideas on why the circuit would work when powered through the 9V battery + Arduino board instead of through the 9V battery + voltage regulator?

You wired up the voltage regulator wrong?

I don't think I wired it up wrong. I tested the voltages with a volt meter. Everything seems fine there.

Did you connect the regulator ground to Arduino ground?

I believe that I tried connecting all of my Grounds together. Why might that make any difference?

All the grounds need to be connected to create a common reference point. Did you include capacitors as shown on the data sheet?

you need to post a diagram of what you tried to do

Adam323: Any ideas on why the circuit would work when powered through the 9V battery + Arduino board instead of through the 9V battery + voltage regulator?

The amount of power the external regulator has to dissipate is much higher than the one on-board the Arduino.

The 3v3 regulator of the Arduino is powered from the 5volt rail. So the power dissipated is 5V-3.3V times the drawn current. Your external regulator is dissipating 9V - 3.3V times the drawn current.

So let's just your transceiver needs 50mA.

Arduino Regulator: (5V-3.3V) * 0.05A = 85mW External Regulator: (9V-3.3V) * 0.05A = 285mW

Pretty large difference.

You didn't give any data on the transceiver, but I would look at how much current it is drawing and see how much power the regulators are dissipating.

Thanks everyone for your help. I think the problem turned out to be the capacitors as was suggested by CrossRoads. I added a 10 uF electrolytic capacitor between output and ground on the 3.3V regulator and everything worked fine after that.

I didn't think about using capacitors in the power supply because I power the Atmega328p chip through a 7805 regulator and have never needed to use a capacitor with that. I got the 7805 from Radio Shack and it didn't even come with a data sheet. It only had a drawing with pin labels on the package.

I suppose it would probably be a best practice to use capacitors in the 7805 circuit as well, even though it seems to be working fine without them.

sonnyyu:

I need to know the approx current-usage in order to choose the right type of battery for my setup.

WIFI-shield might not be good candidate for this type application. by select right type of battery and wireless solution your system could last years, said 10 years.

OP, 9V battery is wrong type of battery for your job. if you give us more detail about your system. We might come out 10 years (per battery replacement) solution for you.

you always need an input AND output capacitor on ANY regulator, lack of an output capacitor gets you a horrible unstable and noisy output and I've seen regs self destruct for lack of an input capacitor.