Logarithm in PBP

[Acetronics2]

This volt i want to show on LCD.

> Where's the problem, then, If you only want to display the voltage ???


But the power change in logarithm scale and this is my problem.

> This needs some USEFUL enlightments ... if you do not need to display the Power !!!

> Do you want to display Voltage in dBv ???

> Do you want to display Voltage in some BARGRAPH mode ??? ...

those ONLY could give any sense to your question !!!

Alain

[savnik]

This volt i want to show on LCD.

> Where's the problem, then, If you only want to display the voltage ???


But the power change in logarithm scale and this is my problem.

> This needs some USEFUL enlightments ... if you do not need to display the Power !!!

> Do you want to display Voltage in dBv ???

> Do you want to display Voltage in some BARGRAPH mode ??? ...

those ONLY could give any sense to your question !!!

Alain

My english is not so good.
I want the voltage which measure with the pic , to show on lcd in dBm or dBv or watt (the table which post in #6)

[ronsimpson]

Savnik,

You need to get a book on basic electronics. Voltage Current Power and Resistance.
Power = voltage * current
In your case you can not see the current so: Power = Voltage * Voltage /Resistance (Voltage squared)
To prove that look at your table. Voltage of 22.4 volts = 10 watts and Voltage of 44.7 volts = 40 watts. Voltage increases 2:1 and power increases 4:1. That proves there is a voltage squared * constant.

Voltage * Voltage/50 = Power

To convert to db is very hard or very simple depending on how you look at it. You can fight BIG math for weeks. When you understand db it is almost as simple as finding Power. I will not tell you how now. You need to think about it for a while.

RonS.

[savnik]

Savnik,

You need to get a book on basic electronics. Voltage Current Power and Resistance.
Power = voltage * current
In your case you can not see the current so: Power = Voltage * Voltage /Resistance (Voltage squared)
To prove that look at your table. Voltage of 22.4 volts = 10 watts and Voltage of 44.7 volts = 40 watts. Voltage increases 2:1 and power increases 4:1. That proves there is a voltage squared * constant.

Voltage * Voltage/50 = Power

To convert to db is very hard or very simple depending on how you look at it. You can fight BIG math for weeks. When you understand db it is almost as simple as finding Power. I will not tell you how now. You need to think about it for a while.

RonS.

I am a electronic for 30 years.
Thank you for your help. You give me some idea how to calculate.

[mackrackit]

Savnik,

Your problem has been bugging me, I like math puzzles, and the post by Pic_User did clear things up.

Now if I understand your table correctly, POWER column is the reading you want and the VOLT column is the value you now have. If this is correct, then keep reading, if not than ...

This is the formula:

Step #1:

D = (VOLTS / 10) * 0.2 'D' is a dummy variable

Step #2:

POWER = VOLTS * D

This give an answer within .1 of the value in the power column.

Hope this helps.

[mackrackit]

I look back and see that ronsimpson said the same thing.

Now you have two ways to do it.

[ronsimpson]

P=v*d, D=(v/10)*.2

P=v*((v/10)*.2)

P=v*v*.2/10

P=v*v/50

[Pic_User]

Hi Savnik,

If I read your problem correctly:

I have a linear for FM and i want to measure the power.
From the power meter i take the indication which is in volt. This volt I want to show on LCD. But the power change in logarithm scale and this is my problem.

My english is not so good.
I want the voltage which measure with the pic , to show on lcd in dBm or dBv or watt (the table which post in #6)

You have a RF amplifier that has an analog power meter. The power meter reads a voltage and displays the power on a Logarithmic scale. The input, to move the meter, is voltage. The scale painted on the meter face is logarithmical.

You need the PIC’s adc input to read the DC voltage running the meter and then using mathematics or a “look-up” table convert the voltage to the equivalent power in Watts. You have already calculated the table, posted in your previous post.

Is this close to the question? I am just trying to help with clarifying the question. Sorry I don’t have an answer for you.

-Adam-

[savnik]

Hi Savnik,

If I read your problem correctly:


You have a RF amplifier that has an analog power meter. The power meter reads a voltage and displays the power on a Logarithmic scale. The input, to move the meter, is voltage. The scale painted on the meter face is logarithmical.

You need the PIC’s adc input to read the DC voltage running the meter and then using mathematics or a “look-up” table convert the voltage to the equivalent power in Watts. You have already calculated the table, posted in your previous post.

Is this close to the question? I am just trying to help with clarifying the question. Sorry I don’t have an answer for you.

-Adam-

Yes, it is my question.