 # Producing sinewave output on Photon

#1

Hey,
I am using a particle photon. I want to generate an output which is in the form of a sine function. It’s not a pure sinewave, but a function of sine and cosine. Right now I am using the analog write feature of zerynth. I tried it with analogWrite(), But I am not getting what I exactly need.
Also, Can I use FFT to generate the output ?

``````import gpio
import dac
import streams
import adc
import math

buf = bytearray(100)
for i in range(len(buf)):
buf[i] = 128 + int(127 * math.sin(2 * math.pi * i / len(buf)))

myDAC = dac.DAC(D8.DAC)
myDAC.start()

myDAC.write(buf,400*len(buf),MILLIS,circular=True)
``````

I tried importing the cosine and sine libraries using,
from math import sin
But that didn’t work either.

#2

Could you specify what kind of error occurs?
What is the output with an oscilloscope?

Also, Unfortunately, Direct FFT is not yet implemented in the MATH library.

#3

Hey, I’ll be more specific here. This is the function to who’s output the output signal should be mapped too.
1.2525*((0.0449949095399884+0.110299998345786cos(tw)-0.0727808875940510cos(2tw)-0.0825773728054780cos(3tw)

In my case, the value of w = 7.5 and t will be the current time. So how do I map the output of this function to the analog write. I plotted the function in matlab using FFT, and both outputs are way different.

#4

Hey. Do you have any idea about it?

#5

I checked your formula using Zerynth studio on my ESP32 Devkit,

``````result= [None]*100
w = 7.5
for j in range(100): #J represents time.
result[j] = 0.0449949095399884+0.110299998345786*math.cos(j*w)-0.0727808875940510*math.cos(2*j*w)-0.0825773728054780*math.cos(3*j*w)
``````

Since the output vary with very small values [-0.1:0.2] you can add scale and bias to the list.
Like multiplying each item in the list with a weight and adding some constant to it,

Then applying the DAC function to that list.
`my_dac.write(result_Scaled,WAIT_TIME,MILLIS,circular=True)`
Let me know if you need further help.