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Hi All,

I need to generate an interrupt pulse on every edge (rising or
falling) of an input signal to a MCU. Any idea how to do this?

Here is the waveform:

foo: --------______--------___________--------

interrupt: -------__-----__------__---------__------


I do have the clock avilable. The interrup pulse has to be at least
200ms wide.

Regards,

SD

you want a monostable flipflop which can be triggered both edges.

possible transistors, opamp, or ic.

ST

just remembered making this once by inverting "foo" so you only
need one trigger direction... i used ot for geting a pulse
from each zero crossing of a 50Hz sine.
look for the common monostable multivibrator circuits and make
the trigger R/C twice. then invert foo and feed it to the triggers inv and non inv.

good luck

--- In Electronics_101@..., "sd7008us" <sd7008us@y...> wrote:

Hi All,

I need to generate an interrupt pulse on every edge (rising or
falling) of an input signal to a MCU. Any idea how to do this?

Here is the waveform:

foo: --------______--------___________--------

interrupt: -------__-----__------__---------__------


I do have the clock avilable. The interrup pulse has to be at least
200ms wide.

Regards,

SD

SD

An exclusive OR gate with the input signal to one side delayed. Do
you really want a 200ms interrupt pulse? That is one seriously slow
processor.

Keith.

--- In Electronics_101@..., "sd7008us" <sd7008us@y...> wrote:

Hi All,

I need to generate an interrupt pulse on every edge (rising or
falling) of an input signal to a MCU. Any idea how to do this?

Here is the waveform:

foo: --------______--------___________--------

interrupt: -------__-----__------__---------__------


I do have the clock avilable. The interrup pulse has to be at least
200ms wide.

Regards,

SD

SD,

An exclusive OR gate would do this by delaying the signal to one input
with a resistor and capacitor (and schmitt trigger if the delay is
long). However, can you not switch the interrupt trigger edge over
each time you detect an edge? Also, a 200ms interrupt seems very long.

Keith.

An exclusive OR gate would do this by delaying the signal to one input
with a resistor and capacitor (and schmitt trigger if the delay is
long). However, can you not switch the interrupt trigger edge over
each time you detect an edge? Also, a 200ms interrupt seems very long.

Keith.

yes that is a way better idea than the monoflop...

ST

Thanks all for the responds. How about we doing the following way?
Would it consider a workaround (not a clean way)?

The foo signal is coming from a push button and we need to interrupt
the MCU every time it changes value. There are two interrupts pins
to the MCU. We also need to debounce the signal after the first
interrupt that is why we need 200ms on the pulse. Here is what we
think will work: we feed the "foo" signal directly to the first
interrupt (Int0) and trigger it on the Negative edge. Then, we
inverted the "foo" and feed the output to the second interrupt
(Int1). The fireware will have to do the extra worrk to track the
states of "foo".

Here is how the waveform would look:

====================================================================

foo: -----------________----------_________-----------
Int0 Int0

/foo: ________----------________------------________
Int1 Int1
=====================================================================

This method only need one interal "PLD" inverter and no external
parts needed.

Any thoughts on this?

Regards,

SD



--- In Electronics_101@..., Stefan Trethan
<stefan_trethan@g...> wrote:

An exclusive OR gate would do this by delaying the signal to one

input

with a resistor and capacitor (and schmitt trigger if the delay

is

long). However, can you not switch the interrupt trigger edge

over

each time you detect an edge? Also, a 200ms interrupt seems very

long.

Keith.

yes that is a way better idea than the monoflop...

ST

Hi All,

It turns out, I only need 600ns delay on the interrupt pulse. What
is the best method to delay the second input signal to the XOR gate?
There is PLD gates avilable in the MCU. Would a series of "AND" does
the job?

Regards,

SD

--- In Electronics_101@..., "Keith" <keith@k...> wrote:

--- In Electronics_101@..., "sd7008us" <sd7008us@y...>

wrote:

Hi All,

I need to generate an interrupt pulse on every edge (rising or
falling) of an input signal to a MCU. Any idea how to do this?

Here is the waveform:

foo: --------______--------___________--------

interrupt: -------__-----__------__---------__------


I do have the clock avilable. The interrup pulse has to be at

least

200ms wide.

Regards,

SD

SD

An exclusive OR gate with the input signal to one side delayed. Do
you really want a 200ms interrupt pulse? That is one seriously

slow

processor.

Keith.

I tried to respond to the post, but has not apeared on the messages
board yet.

Anyway, it turns out I only need 600ns interrupts pluse. Any idea
what is the best way to delay the second input of the XOR gate? The
MCU we are using has PLD gates that we can program. Would a series
of ANDs do the job?

Any ideas??

Regards,

SD

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You might look at the 4528 CMOS multivibrator - it can
be triggered on either a positive or negative edge.
Alternatively, you could make two half monostables and
OR them together. Don Lancaster, in hid book "CMOS
Cookbook" has a pretty good explanation of half
monostables. (4528 would be easier.)

Jim
--- sd7008us <sd7008us@...> wrote:

Hi All,

I need to generate an interrupt pulse on every edge
(rising or
falling) of an input signal to a MCU. Any idea how
to do this?

Here is the waveform:

foo:
--------______--------___________--------

interrupt:
-------__-----__------__---------__------


I do have the clock avilable. The interrup pulse has
to be at least
200ms wide.

Regards,

SD

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At the risk of being branded a microcontroller bigot (I'm not,
really!), why not do this solely in the mcu? Debounce is pretty easy
(most bouncing occurs for about 1-2 mS, according to Horowitz/Hill)
in software. Of course if your MCU is busy doing other things, you
may not be able to watch the switch.

Your dual interrupt idea works though you would need an external
inverter. Can you trigger on leading or training edges? You might
be able to get away with bringing the switch into a port and watching
the transitions on it. If the responsiveness needs only to be in the
100s of mS range, you could poll the pin every 50-100 uS and use a
little state machine to determine switch state (i.e. debounced).

External debounce can also be done with a resistor and a cap. H/H
has a discussion of this. Sorry, I'm too lazy to look up the page.

As usual, there are at least 100 ways to skin this cat.

Phil

--- In Electronics_101@..., "sd7008us" <sd7008us@y...> wrote:

Hi All,

It turns out, I only need 600ns delay on the interrupt pulse. What
is the best method to delay the second input signal to the XOR gate?
There is PLD gates avilable in the MCU. Would a series of "AND" does
the job?

You only need a delay that is long enough to produce the interrupt
pulse width required to trigger the microprocessor. If that is say
250ns, you need to delay by at least that. A resistor to one input of
the XOR gate and a capacitor to ground on that input would do it. A
few AND gates will probably be a bit too quick and produce a rather
short interrupt pulse.

Can you select in software which edge the interrupt triggers on?
Could you debounce the switch in software?

Keith.

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Would a series of ANDs do the job?

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