# Watt meter

#### amirm

Staff Member
CFO (Chief Fun Officer)
And oh, they definitely won't work on DC. They need a varying signal to generate a varying output.

For DC you would need to use a hall-effect sensor.

And oh, the pickups will be sensitive to stray magnetic fields around you. So overall not a good idea.

#### patate91

##### Member
And oh, they definitely won't work on DC. They need a varying signal to generate a varying output.

For DC you would need to use a hall-effect sensor.

And oh, the pickups will be sensitive to stray magnetic fields around you. So overall not a good idea.
For accuracy it's not very important at this point.

But I understand that the meter I'm dreaming of is more complexe than this one.

The goal I was thinking was to get a kind of digital VU meter.

#### solderdude

##### Major Contributor
The meter shown can be used to measure consumed power. It needs to be connected to mains (110V-230V) and uses the input voltage as one of the parameters. It also uses a current probe to measure the current and analyzes phase relation and amplitude of the current compared to the input voltage which also supplies the power for that meter. It thus only works on mains.

I think you mean you want to measure the output power of the amplifier ?
What are you looking to measure ? momentary Peak power ? Peak power per frequency band ? peak hold power levels ? Over what time frame ? average power ? phase shifts between output voltage and current ?

Best would be to use a DAC that measures the input voltage and a current measurement probe clamped over 1 output wire of the speaker cord and let some software do all the calculations for you or do simple math... voltage x current and log that and/or indicate peak levels found.

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#### patate91

##### Member
The meter shown can be used to measure consumed power. It needs to be connected to mains (110V-230V) and uses the input voltage as one of the parameters. It also uses a current probe to measure the current and analyzes phase relation and amplitude of the current compared to the input voltage which also supplies the power for that meter. It thus only works on mains.

I think you mean you want to measure the output power of the amplifier ?
What are you looking to measure ? momentary Peak power ? Peak power per frequency band ? peak hold power levels ? Over what time frame ? average power ? phase shifts between output voltage and current ?

Best would be to use a DAC that measures the input voltage and a current measurement probe clamped over 1 output wire of the speaker cord and let some software do all the calculations for you or do simple math... voltage x current and log that and/or indicate peak levels found.
Yes output power of the amplifier.

I would like to have cool informations. I would want to have a "permanent" installation. Like I said above : a kind of digital VU meter.

Aa you can see my knowledge is limited and I want to know if it's possible, if it exists and if it's affordable.

#### solderdude

##### Major Contributor
I have never seen a true power meter for audio that also measures currents and calculates actual power.
Nor is it really relevant.

There are external power meters that give an indication of power levels but only at a fixed impedance which a speaker is not (unless it is a planar magnetic one). These merely give an indication of the power. This is not the actual power drawn from the amplifier though.

Here there may be some inspiration

#### patate91

##### Member
I have never seen a true power meter for audio that also measures currents and calculates actual power.
Nor is it really relevant.

There are external power meters that give an indication of power levels but only at a fixed impedance which a speaker is not (unless it is a planar magnetic one). These merely give an indication of the power. This is not the actual power drawn from the amplifier though.

Here there may be some inspiration

With computer like Raspberry pi, Arduino, etc. We certainly have enough calculation power at a reasonable price.

#### patate91

##### Member
Same thing goes multimeter : I can buy one from China for about 10\$

#### solderdude

##### Major Contributor
I am afraid you would have to make such a project for it yourself.

The multimeter cannot be used for measuring dynamic (music) signals.
It can only be used for continuous or slowly varying voltages.

You would have to build yourself a peak voltage detector and then would only see peak voltages and not peak power.

#### patate91

##### Member
I am afraid you would have to make such a project for it yourself.

The multimeter cannot be used for measuring dynamic (music) signals.
It can only be used for continuous or slowly varying voltages.

You would have to build yourself a peak voltage detector and then would only see peak voltages and not peak power.

Sadly is out of my reach for now.

#### solderdude

##### Major Contributor
I built one for myself many (about 25) years ago (will have a look if I still have it and post a picture)
It displayed peak power levels and could show a peak voltage (not RMS) as short as a single half sine wave 'pulse'.
Of course the wattage it indicated was actually the voltage level in an 8 Ohm load.
I used it to monitor if my amps reached clipping levels and like seeing 'dancing' VU meters.

#### solderdude

##### Major Contributor
found it... and it still works.

(insert above is rear side)

One can adjust the limit using the knob on the right. For this picture it was set at 165W. For a 50W amp it could be set for 50W and the dot on the far left would indicate the measured output (peaks can exceed the nominal rating of an amp). This way its was very easy to monitor output power.
Still works ... not using it any more.

Below what's inside.

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#### renaudrenaud

##### Member
I have done things with Arduino.