Beginner circuit help.

[Dan Schuman]

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?

 

[Randy Day]

[snip]

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.

Assuming you mean to use the LED across the 12v
supply, you use Ohm's Law like this:

Supply voltage - Led voltage 12 - 3
R = ---------------------------- = ------ = 450
LED current .02

Then use a 470 ohm standard value resistor in
series with the LED, like so:

+12v -----[R]----|>|---- Gnd
| LED
Spkr
|
Gnd


HTH

 

[Eeyore]

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.

You haven't even said what you want to do with the speaker and led !

Graham

 

[Eeyore]

+12v -----[R]----|>|---- Gnd
| LED
Spkr
|
Gnd

And putting DC through the speaker will achieve what exactly ? Other than
heating the voice coil and draining the battery.

Graham

 

[Randy Day]

+12v -----[R]----|>|---- Gnd
| LED
Spkr
|
Gnd

And putting DC through the speaker will achieve what exactly ? Other than
heating the voice coil and draining the battery.

He referred to a '12v' speaker; I'm guessing he
means a powered speaker/amplifier. If I'm wrong,
it's still a learning experience.

 

[neon]

lame idea a speaker is an ac device works fine with ac put your 9v battery and poof no speaker. the LED is a dc device even though it can be modulated you /I can see it for the same reason I CANNOT SEE 6O HZ LAMPS FLASHING. VERY DENSE.