On Monday, 20 March 2017 13:17:55 GMT Ralph Corderoy wrote:
> So bounces can reach that simple callback that printed the current time
> in your cut-down Python test program?

Hopefully, once by debouncing circuit is complete, there'll be no bounces that 
are worth worrying about.

Something else occurred to me regarding the Schmidt Trigger inputs.  I've used 
these device in the past and, as Peter mentions, they sharpen the edges and 
ensure more consistent cross-over times as the signal traverses the threshold.

In this case, I don't care if the GPIO I/P detects the rising edge after 1 us 
or 100 ms; the user is unlikely to notice the extra delay :-)

What I do care about is those super-sharp edges.  I recall that when I worked 
on an early digital test system in the eighties, the maximum speed that the 
pulses could be clocked out was 100 MHz.  The edges were 'fairly rounded' but 
certainly reached the max well before the 10 ns pulse started to go down 
again.  We were having mega cross-talk problems until we did the sums and 
realised that those sharp edges contained harmonics up to 1.2 GHz!  The wires 
in our interface hardware were acting as excellent aerials ;-( 

Funnily enough the clock speed of the Pi is around 1 Ghz ....

>     Wimborne Model Town is open between 1 April and March 19th and 29
>     October daily

March 19th was last year.  It's 1st April this year.

> Assuming `29 October' is correct, DST will end in the early hours on
> that day.  ;-)

Of course.  We designed it that way :-)  If there is anyone still braving the 
elements by then, I doubt that they will worry too much if the clock is an 
hour out.  

As far as I know the Pi deals with DST anyway, but I'm unsure if that applies 
when an external Real Time Clock is in use.  I don't see why it shouldn't.

-- 



                Terry Coles

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