[Tutor] Associate decimal values with an integer range

[sparkle Plenty]

On Tue, Apr 30, 2013 at 2:13 PM, sparkle Plenty <
sparkle.plenty12481632 at gmail.com> wrote:

>
>
> On Mon, Apr 29, 2013 at 11:27 AM, Oscar Benjamin <
> oscar.j.benjamin at gmail.com> wrote:
>
>> On 29 April 2013 15:28, sparkle Plenty <sparkle.plenty12481632 at gmail.com>
>> wrote:
>> > Hi, I need some hints on where to start solving this problem.
>> > I have to interpret a one-byte floating point number as a range between
>> 0
>> > and 240.  This is for a gui that controls an amplifier.  I am getting a
>> > value such as 0.8367 from a fader control, and my Python is
>> interpreting it
>> > as either a 0 or 1.  I need to define this number to Python as an
>> integer
>> > value between 0 and 240.  I know that in hex I have the potential for
>> > numbers from 0 to 255 within my one byte of available space, and the
>> value
>> > will be sent from gui to amp and back as a packed one-byte number.  I
>> have
>> > looked at the math module and so far, I am still stuck.
>>
>> You need to define the range of values that you will accept. If you
>> want the floating point numbers to map linearly to integers you can
>> then use:
>>
>> byte = int(241 * float_value / max_float_value)
>>
>> This will give a value between 0 and 240 inclusive for any positive
>> float_value that is less than max_float_value. The integer values will
>> be approximately proportional to the float values.
>>
>> You may also want to check for overflow:
>>
>> byte = min(byte, 240)
>>
>> > Alas, business calc was a long time ago, and I never studied
>> logarithms.  I
>> > expect the answer would be easier to find if I had more math.
>>
>> Logarithms would be useful for a different (non-linear) type of
>> scaling. I can't tell you whether or not you want logarithmic scaling
>> since I'm not sure what the byte integer is needed for. If you did
>> want to use logarithmic scaling then you could do something like:
>>
>> byte = int((241 / math.log(2)) * math.log(1 + float_value /
>> max_float_value))
>>
>>
>> Oscar
>>
>
> Thanks!
>

Sorry for the ambiguity.  The device is an amplifier, a fader is a control
on the amplifier, the input is from a gui, and arrives as a floating
point number, and the output goes to the amplifier.  Some of the faders
take a range from -40mH to 20mH, and others have different ranges.  I
receive a floating point number from the gui and need to represent it in
one packed hex byte between x00 and xff.  I have solved the problem of how
to adjust the values, now I have to figure out how to translate it into
Python.

Thanks again for all your help.  I appreciate it.
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