[sdiy] Clock signal detector

[Magnus Danielson]

Dave Manley wrote:
> 
>>
>> 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...!
> 
> Try using a series diode, to a resistor and cap to ground.  When the 
> signal is high it charges the cap, when low the resistor drains the cap. 
>  Choose the R to drain the cap if the clock stops for a few ticks.  Put 
> a schmitt before and after.

I agree. I was thinking the same thing. Possibly use the spare drivers 
to bring more UMPF to the charge side but just putting a few in parallel.

Cheers,
Magnus