There's something up with this, the LS02 is actually a NOR gate, and
the LS04 is an inverter. I guess the IC's are labeled backwards?
You definitely want to change the inverter to an LS14, which is a
'Schmitt trigger' input, it has hysteresis on the input.
Meaning that if the output is low, it will take eg. <1V to make it go high,
and if the output is high, it will take eg. >3V to make it go low.
This dead band gives excellent noise rejection as the input needs
to move eg. 2V for the output to change.
I've used 1V and 3V as examples, the data sheet for the IC has exact values.
As Rodger said, 1uF or maybe more is good for the caps also.
If you have further noise problems you could also put 100uF locally between the '+5v'
above the 1K resistors, and to the local ground in case there is +5v rail noise.
Marc
modified circuit:
Both of the buttons connected to ground will produce a logic low output.
None or one button connected to ground will not change the output (will stay high)
The output isn't a 'pulse', it will stay low while both buttons are held down together.
(is this the way it's supposed to work?)
> >
> > +5v
> >
> > | |
> > \ \
> > / / 1K
> > \ \
> > / / LS14
> > | | 220 Ohm (inverters) ____
> > Start 1 []------+-----/\/\/\/--+--------|>o-------| \
> > | | |LS02|-- output
> > Start 2 []---------+--/\/\/\/------+----|>o-------|___/
> > | | (NOR)
> > - - 1µF
> > - -
> > | |
> > === ===
> > = =
> >
original circuit:
> >
> > +5v
> >
> > | |
> > \ \
> > / / 1K
> > \ \
> > / / LS02
> > | | 220 Ohm (inverters)
> > Start 1 []------+-----/\/\/\/--+--------|>o-------|~~~\
> > | | |LS04|-- output pulse
> > Start 2 []---------+--/\/\/\/------+----|>o-------|___/
> > | |
> > - - .1µF
> > - -
> > | |
> > === ===
> > = =
> >
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Received on Mon Sep 3 18:06:46 2001
This archive was generated by hypermail 2.1.8 : Fri Aug 01 2003 - 00:33:41 EDT