[Discuss-gnuradio] Problems with scopesink

[Chiara De Dominicis]

Hi everyone!
I am new to gnuradio (I' m working with it for my thesis) and I have some problems with gr.sig_source_c + scopesink.
I would like to plot the generated complex source (real and imaginary part) in scopesink2.scope_sink_f but it doesn't work if I don't add a second sink (audio.sink) which I don't really need.

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src0 = gr.sig_source_c (sampling_freq, gr.GR_SIN_WAVE, frequency, ampl)
dst = audio.sink(sampling_freq)

class demo_graph(stdgui2.std_top_block):
    
    def __init__(self, frame, panel, vbox, argv):
        stdgui2.std_top_block.__init__(self, frame, panel, vbox, argv)
        real = gr.complex_to_real() 
        compl = gr.complex_to_imag()
        scope = scopesink2.scope_sink_f(panel,"Input -> USRP", sampling_freq, num_inputs=2 )
        vbox.Add(scope.win,1,wx.EXPAND)
        self.connect(src0, real)
        self.connect(src0, compl)
        self.connect(real, (scope,0))
        self.connect(compl, (scope,1))
        self.connect(real, (dst,0))
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This is the working code but if I comment the last line the scopesink seems "freezed" and I can' t even close it.
What's wrong with my code?
Can I use scope_sink_c instead of scope_sink_f? How?

Thanks in advance
Chiara