Okay so would it be possible to design something like the attached picture but instead of USB it would be hooked inline between a 12v car battery and a stereo anplifier?
Yes you can do that , with say an AC723 Hall effect sensor ( if it does the correct current range you want) for measuring the current.
Not sure what you expect to see tho, you will only see a value that goes up a bit when you crank the volume up.
simple answer: sure
measure the voltage drop across a shunt of known ohmic value to calculate current and power dissipation.
not gonna give you audio power output of the amp, but consumption/dissipation estimate. also not gonna give MAH capacity of battery.
Could be good if you want to go big on the subs and need to know if you need more power???
My thoughts behind it is I'd like to see my actual wattage being produced from my amp at any given time.
your amp does not produce wattage it consumes it. ... are you trying to measure output wattage out of your amps into the speakers?
Yes the output wattage from amp to speakers
this is not a simple task due to complex frequency and ac output. It's not simple ohms law. You can measure it based on a certain sine wave or something like that but it's meaningless to have a output wattage meter that gives you a figure.
It's fairly easy to measure the power going IN to the amplifier because it's still more or less DC at that point. Then you can guess at how efficient the amplifier is to give you a figure for the output power.
But that doesn't tell you a lot about the sound output because speakers are seriously inefficient so you get relatively little sound power out compared to the input power to the speakers.
Steve
Yes the output wattage from amp to speakers
Then, you'd connect it between the amp & speakers. As you probably know, the audio signal is AC so you'll have to rectify or otherwise deal with that.
Is this for music or is for precise testing with test-tones?
Music has a peak-to-average ratio of about 20dB (10:1). That means if your amp is putting-out 100W on the peaks, it's putting-out about 10W average.
Typically we want to know the peak power because if you "try" to exceed the peak capability of the amplifier you get [u]clipping[/u] (distortion).
The easiest thing to do is measure the voltage and then calculate power.
Power (Watts) = V2/R (Where R is the speaker impedance*)
Or, P = I2R (I is current)
Or, P = V x I
You can use Ohm's Law to calculate the "nominal" current.
You can make a [u]peak detector[/u] which will give you an easy-to-measure, slowly-varying, positive DC voltage equal the peak. (The basic peak detector simply ignores the negative-half of the AC signal, but the negative peak should be approximately equal to the positive peak.)
The peak of a sine wave is about 1.4 times RMS, so multiply by 0.707 to get the "equivalent" RMS. (With regular audio, the true RMS is about 20dB lower because of that peak-to-average ratio.)
Of course, you'll need a voltage divider (2-resistors, usually in front of the peak detector). The maximum voltage into the Arduino is 5V (which is in the ballpark of 1W). so, you'll need to include the voltage divider and the .707 factor in your calculations.
- Speaker impedance isn't pure resistance, it's not exact, and it's not constant over the frequency range. So, the actual current or power may not be exactly what you calculate. But, speakers are tested and specified at "constant" voltage "assuming" the nominal impedance. In most cases you can do the same thing... Just use the voltage, and ignore the actual current and actual impedance.
Thanks for the info guys! I actually found what I needed on another forum. This has already been done by the SMD-AMM1 multimeter. I just have to find a way to make it smaller to mount in my dash the way I want it.