Electrical Question

[theshoeshineman]

I'm just trying that doorbell mod where you turn a doorbell into a on/off remote and got a doorbell which takes 3 x 1.5 volt batteries and a 5 volt relay.

Problem is, when I opened it up, there is a wire going to part of the circuit board after the second battery (3volts).

What resister would I need to drop the current enough to power the 3volt side of the board.

I don't know what current is being pulled :(

[theshoeshineman]

Also when I put my multimeter accross the + and - of my speaker when the musics playing I'm only reading 1/2 a volt? Doesn't that need to be 5volts to work :| eeep!

[XcOM]

the board will provide whatever power is needed for the speaker to work, really it dosen't matter, aslong as its not greater than 5v you shouldn't damage your hardware, it only needs to complete a circuit.

and by my calculations 5volt DC to 3vDC would require a 680 ohm resistor, the colour code for 680 is "blue grey brown"

i think a 1/4W resistor will do as it will dissipate 6.12 mW and should draw a max current of 3 mA.

But please check the current being pulled first to ensure you are using the rite setup. im sure someone more experienced than me will let you know if im wrong

[Killa_Ape]

You could try the resistor and if it's drawing too much current the resistor will start glowing a nice orange colour kind of like a LED ;p
With past experience you'll burn up a resistor and everything else should be fine, but use at your own discretion kind of thing ;p

If you have your meter hooked in correctly and you are not getting a current reading it could be too low for your meter to register the current. (I'm assuming you got a cheap one not like a 500$ meter so)

[xmastree]

and by my calculations 5volt DC to 3vDC would require a 680 ohm resistor, the colour code for 680 is "blue grey brown"
But that assumes the current is 3mA. We don't know that.

If part of the circuit needs 3V, and you only have 5V available (you are using 5V, aren't you?) then the best way is to put three silicon diodes in series. Something like 1N4148 will be fine. Each one will drop 0.6V no matter what current is passing through it, unlike a resistor. Three of them in series will drop a total of 1.8V, which will give you close enough to 3V.

Or you could use a LED with a drop of 2V...

[XcOM]

cheers xmastree, i didn't think of that, i assumed the standard current from 5v rail, your soloution is much better than mine and will do the same job.

+rep