[sdiy] Clock signal detector

[Scott Gravenhorst]

James Dunn <james at 4thharmonic.com> wrote:
>Hi,
>
>I want to make a simple circuit to detect when a clock signal is 
>present. The clock line is either at 0v or a pulse of about 15% duty 
>cycle and around 4 hz. I want a control output of 1 for clock present 
>and 0 for no clock present. How is this done? It would be great if I 
>could do it with 3 or 4 schmitt triggers and/or 1/4 of a 4016 analogue 
>switch as that is what I have left...!
>

A retriggerable one-shot could work, the clock feeds the trigger input which keeps
the one-shot in a triggered state until the clock stops, then the one-shot changes
to it's "resting" state.  The output of the one-shot is "clock running".

-- ScottG
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-- Scott Gravenhorst
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