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I'm working on a circuit to help learn all this jazz, and wonder how this could be accomplished:

Two devices to be used on the circuit are a speaker and an LED.

Source: 12V battery (Two 1.5V + 9V batteries)

LED: 3V / 20mA Speaker: 12V / 15mA

(I am aware these devices operate at varied amperes and such, but I would ideally like these to work at these specific values for educational purposes.)

How could I design a circuit that houses both these devices at their rated amps? Right now I'm putting a parallel circuit near the beginning to cut up the amperes, but then I seem to get stuck when trying to use the lower voltage device at 20mA.

Any help?

Reply to
Dan Schuman
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What you ask for is nearly meaningless. Either you are very confused or you are stating things very poorly.

An LED data sheet may show the thing flowing a certain amount of current at a certain voltage, but the current in a device is always a function (usually monotonically increasing) of it's voltage, and visa-versa. If you have an LED that's rated at 20mA at 3V, then use some basic circuit theory, figure that after the lamp takes 3V away from 12V, you're left with 9V to drive 20mA through a resistor -- then figure out the necessary resistance.

Speakers don't operate from DC. Either you have something like a piezo buzzer (which is a 'speaker' _and_ an oscillator), or you misunderstand something. At any rate, if the device is rated at 12V, then it will pull an appropriate amount of current when you connect it across a 12V supply.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

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