ELM409
Example Applications (continued)
The following are a a few circuits that use the
ELM409, but may not be what comes to mind when
you think of debouncing. They take advantage of the
internal timers in the ELM409 as well as the ability to
change options while the circuit is operational, to
provide some interesting functions.
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The first (Figure 8) is a circuit that simply connects
the debounce input to the positive supply. With the
debounce period set for 500 msec, the output will
initially be low, then go high 500 msec after the power
is turned on. This delay may be useful if trying to
sequence the power to different circuits, or enable the
outputs (audio power amplifiers often need this delay
to allow the supplies to settle before connecting the
amplifier outputs to the speakers).
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Figure 8. Power on delay
Figure 9 shows a circuit that provides a single
50 msec wide pulse at the output, 25 msec after power
has been applied. It relies on the fact that the
ELM409’s pin 7 output is always at a low level on
power up (and pin 6 is always high), so the initial
options setting will then be 010, for a 50 msec pulse
after a 25 msec debounce period. Once the output
pulse begins, however, the connection from pin 7 to
pin 4 causes the options to change to 011, giving a
debounce period of 500 msec (which can never be
met by a 50 msec pulse). The output remains low from
that time on.
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This circuit works because the option pins are
always read just before a 25 msec debounce period is
about to expire (allowing for changes ‘on the fly’). In
this case, the pulse output is at its midpoint when the
pins are read, so the new latched setting becomes
011, and the debounce period changes to 500 msec.
As the pulse never lasts that long, it is ignored by the
500 msec debounce circuit, and the output never
changes again.
Figure 9. Power on pulse
The final circuit also uses the output to modify the
input, and the debounce period. The result is a series
of 25 msec pulses with 500 msec gaps in between,
that continually repeat. Low frequency oscillators such
as this may be useful on the test bench, or it may
simply be used to drive an LED in order to attract
attention.
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These are just a few of the many applications
possible with the ELM409… Enjoy!
Figure 10. Low frequency oscillator
ELM409DSA
Elm Electronics – Circuits for the Hobbyist
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