KB6NU's Ham Radio Blog

///////////////////////////////////////////
Not enough bounce

Posted: 11 Jul 2016 12:17 PM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Last year, I wrote about a problem that a friend of mine was having with a
bouncing switch input. I searched the web, found the circuit at right, and
proceeded to breadboard it for him. We put the scope on it, and it seemed
to work great.Â*A couple of weeks later, however, he called and said that
when he tried using it in his math camp class, it didnt work at all.

A couple of days ago, I got an e-mail from my friend, saying that it was
time for math camp and could we take a look at the debounceÂ*circuit again.
This time, we connected the circuit to the input of a 74LS640 transceiver,
as he did last year. Sure enough, it just didnt seem to switch at all. When
I put the scope on it, I found that with the switch closed, the voltage on
the output only got down to around 3 V or so.

Im kind of confused by this. Is the IC input actually sourcing enough
current to keep the output at 3 V?

What we ended up doing is wiring up a transistor switch on the
debounceÂ*circuit output. That works just fine, but seems kind of kludgeyÂ*to
me.

The post Not enough bounce appeared first on KB6NUs Ham Radio Blog.