voltage drop?

I'm just trying to supply power to a microcontroller. I have a 9v battery that's actually at 6.3 V, so I made a voltage divider to get it under 5.5v. Here's the weird thing, I unplugged the plus voltage and ground wires from the breadboard and tested the voltage at it showed me 5.1v. As soon as I plug them in, I get 1.2 v! Even on the micro pins! Is my breadboard doing something funny? Is this supposed to happen?

Voltage dividers won't regulate the input voltage at all.

If your 9v is dying you might see the voltage drop when loaded with the circuit while seeing a higher voltage with the meter (the meter is high impedance)

I recently found that I have an electrolytic capacitor on a board was backwards -- everything worked great then for no reason I had a short between power and ground.

If your board is powering something else you might have a short??

I new that voltage dividers won't care about the input voltage but I though that the battery voltage wouldn't change with a load. Well, it does. Time to think of a different plan :)

Near the end of life battery voltages will become less reliable.

You can't use a voltage divider to feed any amount of current anyway, the voltage will 'pull' as the load increases and will depend on the current and the values of the resistors. The easiest way to provide 5v is through a voltage regulator. A 7805 is pretty cheap.

http://en.wikipedia.org/wiki/78xx

Exactly, any resistance at the output of the voltage divider, will have to be calculated as a parallel resistor to R2.

Yeah. I was sort of being lazy and trying to avoid asking my parents to drive me to radioshack.

Standard 9 volt batteries are a poor choice for powering an Arduino board. They have low current capacity and are probably the highest cost battery per MAH ratings. A DC 'wall wart' power supply (9vdc @ 1amp) would be a real cost saver over time, but don't get it at radio shack as they are vastly priced there, on line is your friend.

If you must go with non-rechargable batteries you would be much better off using AA size batteries, using 6-8 of them in a series cell arrangment with a suitable batter holder.

Lefty

wall warts can be had also, they tend to pile up in a residence, as long as it is < 12 volts and >= 500 ma, preferably switching (really small vs box) and DC current you can run it into a 7805 (i use a 9v 1 amp answering machine one)

also making your own little dc to dc regulator out of a few $ worth of radio shack parts (with some left over) is a rewarding experience while lasting a long time