Logarithm in PBP

[Acetronics2]

Hi, Savnik

Jerson is right ... the simplest Pic way is to build a retrieving table.

IN PbP that's called LOOKDOWN2 ... ( catches the closest values, sup and inf ... just think to use a clever index !!! )

Then just have to add a linear approx. between table values ...


Buuuuuut, My old brain tells me it is very easy to do it with 3or4 couples of linearising resistors and diodes ...

or to use a logarithmic AOP !!!

Last and simplest solution: The App Notes of ICL 7106 or 7136 show a logarithmic scale design ...

Which is closest to your requirements ??? ...

Alain

[savnik]

Hi, Savnik

Jerson is right ... the simplest Pic way is to build a retrieving table.

IN PbP that's called LOOKDOWN2 ... ( catches the closest values, sup and inf ... just think to use a clever index !!! )

Then just have to add a linear approx. between table values ...


Buuuuuut, My old brain tells me it is very easy to do it with 3or4 couples of linearising resistors and diodes ...

or to use a logarithmic AOP !!!

Last and simplest solution: The App Notes of ICL 7106 or 7136 show a logarithmic scale design ...

Which is closest to your requirements ??? ...

Alain

I have make a table.
I want to measure the volts at the input of pic , and show on LCD the power

POWER	VOLT		POWER	VOLT
1	7,1		26	36,1
2	10,0		27	36,7
3	12,2		28	37,4
4	14,1		29	38,1
5	15,8		30	38,7
6	17,3		31	39,4
7	18,7		32	40,0
8	20,0		33	40,6
9	21,2		34	41,6
10	22,4		35	41,8
11	23,5		36	42,4
12	24,5		37	43,0
13	25,5		38	43,6
14	26,5		39	44,2
15	27,4		40	44,7
16	28,3		41	45,3
17	29,2		42	45,8
18	30,0		43	46,4
19	30,8		44	46,9
20	31,6		45	47,4
21	32,4		46	48,0
22	33,2		47	48,5
23	33,9		48	49,0
24	34,6		49	49,5
25	35,4		50	50,0

[Acetronics2]

May I suppose the number in the "Power" column has to be displayed ... or is it just your Index ???

In this case ... It would be much easier to use if the "Volts" were integers numbers and "Power" decimals ... I know: some more work for you !!!

Alain

See Also Here : http://curveexpert.webhop.net/

That Helps ... isn't it ???

Quadratic Fit: y=a+bx+cx^2 ( y: Power ; x :Voltage )
Coefficient Data:
a = 0.00076569488
b = -8.0880958e-005
c = 0.019999816

[savnik]

May I suppose the number in the "Power" column has to be displayed ... or is it just your Index ???

In this case ... It would be much easier to use if the "Volts" were integers numbers and "Power" decimals ... I know: some more work for you !!!

Alain

See Also Here : http://curveexpert.webhop.net/

That Helps ... isn't it ???

I display only the volts

[Acetronics2]

I display only the volts

read from previous posts :

<< I want to measure the volts at the input of pic , and show on LCD the power >>

Could you give me a decent explanation ???

Alain

[savnik]

read from previous posts :

<< I want to measure the volts at the input of pic , and show on LCD the power >>

Could you give me a decent explanation ???

Alain

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.

[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