how to get 3.7V on the arduino?

Hello. I dismantled my old 512MB trekstore mp3 player to use with the arduino :smiley:
But I don't want to use the extra 3.7V battery of the mp3 player. I want to power himthrough the ARDUINO ;D
But how to get 3.7V?

3.3V is too low...
so I would need an 240 000 Ohm resistor on the 5V line to the mp3 player. But I don't think that this is a rather good solution? Or is it ok? Or is there something like an 3.7V regulator?

Use an adjustable regulator. Resistors are used to set the output voltage.

It may need to be a low dropout regulator (LDO) to be able to properly regulate the small difference between 5V and 3.7V.

The LM317 is the only adjustable regulator I know off the top of my head, but I don't recall what the dropout voltage is.

-j

You could use 2 diodes in series to get something closed (3.6V). Each diode drops voltage by 0.7 volts.

5v ------|>|---|>|----- 3.6V

GND --------------------

So I shouldn't use an 240k[ch937] resistor? I want to learn more about electronics and I am searching for a good book right now on it. But can please someone briefly tell me why it's stupid or inappropriate to use a resistors for this?

Are there diodes which drop the voltage less than 0.7 volts? Because I used an multimeter and my arduino board only outputs 4.93V and the mp3-players battery outputs 3.75V.
And 4.93V -2*0.7V = 3.53V is too low, or not?

I googled. :smiley: The LM317 can deliver an output voltage between 1.25V and 37V. (LM317 - Wikipedia)
But I have no clue how to adjust the voltage, because it has only 3 legs and no potentiometer:
leg1: adj
leg2: vout
leg3: vin

Are there diodes which drop the voltage less than 0.7 volts? Because I used a multimeter and my arduino board only outputs 4.93V and the mp3-players battery outputs 3.75V.
And 4.93V -2*0.7V = 3.53V is too low, or not?

There are diodes that only drop 0.3 volts. You could use one 0.7 and 2 x 0.3 to drop 1.3 volts.

I think you won't have any problem. That 3.7 volts battery is (almost sure) a Li-Ion one. Li-Ion batteries work between 4.2 (full) and 3.5 (almost depleted) volts. You should try to use a 5v regulated power supply, connect the 2 diodes and test your mp3 player. Just make sure you are getting 3.6 volts before connecting it to the mp3 player.

I googled. Cheesy The LM317 can deliver an output voltage between 1.25V and 37V. (LM317 - Wikipedia)
But I have no clue how to adjust the voltage, because it has only 3 legs and no potentiometer:
leg1: adj
leg2: vout
leg3: vin

read LM317 datasheet. You need two resistors to configure the output voltage.

But can please someone briefly tell me why it's stupid or inappropriate to use a resistors for this?

A resistor drops a voltage that depends on the current flowing. This current will change as you do things like change the volume, stop and start playing turn on and off the display. Therefore the voltage supply will be up and down faster than a (censored image of a lady of the night's under garments).
So you need something that reduces the voltage independently of the current. Such a thing is a diode or a voltage regulator. The only thing you should ever consider powering by a dropping resistor is something that takes constant current and then when you have considered it, don't.