Re: [Discuss-gnuradio] create lookup tables

[Andreas Ladanyi]

Hi Marcus,
>  Well, first:
> Signal Source can't produce 8bit signed integers by itself, so you'll 
> have to convert whatever you configure the signal source for to char, 
> eg. you could set it to "float" and use the "float to char" 
> conversion. Make sure the result has amplitude 127. Properly configure 
> your signal source for the desired sine period, e.g. sample_rate=X , 
> frequency = X/256.
So if i want to have a sine with frequency 1 hz and 256 samples per sine 
period i have to set samplerate to 256 ?

1hz = 256/256
> Then, use a "head" block with that period, and pipe the result to a 
> file sink; use the char/byte type of everything. Done. Pretty 
> straightforward, I guess :)
The head block has 2 parameters: number of items, vector length

The number of items is the amount of samples for a sine period = 256 in 
this case ?

> As a side note: that's really a bit of a corner use case; a single 
> line of python would probably be easier:
>
> import numpy
> (numpy.sine(numpy.linspace(0,2*numpy.pi,256)) * 
> 127).astype(numpy.int8).tofile("/tmp/sinetable.dat")
This works perfect. Now i have a table with one sine period.

Now this is non specific gnuradio question, but how is it possible with 
python to create a sine with 1 hz from this lookup table.

My first idea is: python has to sample the 256 samples (for one period)  
from lookup table in exactly one second. So i think i need a timer which 
calls the next sample in the lookup table all 3,9 ms.
> in C, that program wouldn't be much longer.
and maybe faster ?!
> Best regards,
> Marcus
regards,
Andy :-)