I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally it's
opened with remote control but for visitors during office hours is was
equipped with a bell push for entry and exit, this being cheaper than
induction loops etc.

Some wag has found that if the outside button is depressed and held down the
gate cycles through open to closed and then will not accept input from the
other button or the remotes.

I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about 30 quid
and I wonder about something simpler?

AJH

andrew wrote:
I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally it's
opened with remote control but for visitors during office hours is was
equipped with a bell push for entry and exit, this being cheaper than
induction loops etc.

Some wag has found that if the outside button is depressed and held down the
gate cycles through open to closed and then will not accept input from the
other button or the remotes.

I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about 30 quid
and I wonder about something simpler?

AJH
Make the bellpush live, then it will only be held down momentarily.

Bill

Bill Wright wrote:
andrew wrote:
I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally it's
opened with remote control but for visitors during office hours is was
equipped with a bell push for entry and exit, this being cheaper than
induction loops etc.

Some wag has found that if the outside button is depressed and held
down the
gate cycles through open to closed and then will not accept input from
the
other button or the remotes.
I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about 30
quid
and I wonder about something simpler?

AJH
Make the bellpush live, then it will only be held down momentarily.

Bill


simplest is a resistor a capacitor and a pair of CMOS gates.

You might need a buffer with some current to drive anything of any use.

SEE http://www.electronics-tutorials.ws/...onostable.html

and "NOR gate monostable".

"The Natural Philosopher" wrote in message
...

andrew wrote:
I'm looking for the simplest monostable to provide a short pulse to


simplest is a resistor a capacitor and a pair of CMOS gates.

How about just a large capacitor? Normally connected to a power supply,
pressing the button (a changeover switch) connects one end to a relay
instead (the other end is common). Value and relay (and perhaps series
resistor) chosen to provide a long enough pulse.

This doesn't stop someone pressing repeatedly, but neither does a
monostable, unless you have a second monostable that stops you operating the
switch again for a longer period.

--
Bartc

On 04/02/2012 00:04, The Natural Philosopher wrote:
Bill Wright wrote:
andrew wrote:
I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally it's
opened with remote control but for visitors during office hours is was
equipped with a bell push for entry and exit, this being cheaper than
induction loops etc.

Some wag has found that if the outside button is depressed and held
down the
gate cycles through open to closed and then will not accept input
from the
other button or the remotes.
I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about
30 quid
and I wonder about something simpler?

AJH
Make the bellpush live, then it will only be held down momentarily.

Bill


simplest is a resistor a capacitor and a pair of CMOS gates.

You might need a buffer with some current to drive anything of any use.

SEE http://www.electronics-tutorials.ws/...onostable.html

and "NOR gate monostable".

He might even get away with a dc supply, the pushbutton, a blocking
capacitor, a drain resistor and a relay. Simple and bombproof.

SteveW

BartC wrote:
"The Natural Philosopher" wrote in message
...

andrew wrote:
I'm looking for the simplest monostable to provide a short pulse to


simplest is a resistor a capacitor and a pair of CMOS gates.

How about just a large capacitor? Normally connected to a power supply,
pressing the button (a changeover switch) connects one end to a relay
instead (the other end is common). Value and relay (and perhaps series
resistor) chosen to provide a long enough pulse.

This doesn't stop someone pressing repeatedly, but neither does a
monostable, unless you have a second monostable that stops you operating
the switch again for a longer period.

I think the condition to stop is jamming the button down.

You are right that a capacitor with a leaky resistor across it that is
connected in series with a relay wont hold the relay in for ever. If te
resistor is relatively large you will have to wait a fair time before it
works again, too.

andrew wrote:

I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally
it's opened with remote control but for visitors during office hours
is was equipped with a bell push for entry and exit, this being
cheaper than induction loops etc.

Some wag has found that if the outside button is depressed and held
down the gate cycles through open to closed and then will not accept
input from the other button or the remotes.

I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about
30 quid and I wonder about something simpler?

If you are into electronics, a 555 can do that fine.

There's an example in the app note.

Steve Walker wrote:

On 04/02/2012 00:04, The Natural Philosopher wrote:

simplest is a resistor a capacitor and a pair of CMOS gates.

You might need a buffer with some current to drive anything of any use.

SEE http://www.electronics-tutorials.ws/...onostable.html

and "NOR gate monostable".

He might even get away with a dc supply, the pushbutton, a blocking
capacitor, a drain resistor and a relay. Simple and bombproof.

SteveW

I was considering just this and rummaging through my failed projects box I
have a Hamelin HE3312A 12V reed relay donated by a denizen of this group.

It seems to have a coil resistance of 500 Ohm and I think holding on the
contacts for 100millisec would trigger the gate. It latches at 3.75V and
the initial current will be 24mA but what size of capacitor? What size
resistor to leak the capacitor to ground? I'd guess it needs to be an order
of magnitude bigger than the coil resistance?

AJH

On Sat, 04 Feb 2012 16:08:12 +1100, Rod Speed wrote:

andrew wrote:

I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally it's
opened with remote control but for visitors during office hours is was
equipped with a bell push for entry and exit, this being cheaper than
induction loops etc.

Some wag has found that if the outside button is depressed and held
down the gate cycles through open to closed and then will not accept
input from the other button or the remotes.

I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about 30
quid and I wonder about something simpler?

If you are into electronics, a 555 can do that fine.

There's an example in the app note.


Velleman do a neat astable "flasher" kit with a relay output. It might be
possible to do a bit of pcb modification to turn it into a button-
triggered monostable. OTOH a bit of stripboard is pretty cheap. :-)


--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On 04/02/2012 14:23, andrew wrote:
Steve Walker wrote:

On 04/02/2012 00:04, The Natural Philosopher wrote:

simplest is a resistor a capacitor and a pair of CMOS gates.

You might need a buffer with some current to drive anything of any use.

SEE http://www.electronics-tutorials.ws/...onostable.html

and "NOR gate monostable".

He might even get away with a dc supply, the pushbutton, a blocking
capacitor, a drain resistor and a relay. Simple and bombproof.

SteveW

I was considering just this and rummaging through my failed projects box I
have a Hamelin HE3312A 12V reed relay donated by a denizen of this group.

It seems to have a coil resistance of 500 Ohm and I think holding on the
contacts for 100millisec would trigger the gate. It latches at 3.75V and
the initial current will be 24mA but what size of capacitor? What size
resistor to leak the capacitor to ground? I'd guess it needs to be an order
of magnitude bigger than the coil resistance?

AJH

You've mentioned 3.75V, but it's not clear whether that is the pull-in
or drop-out voltage, so I've used it for both and you'll have to adjust
values where necessary.

I've totally forgotten my capacitor charge equations so I took a look at
http://hyperphysics.phy-astr.gsu.edu...ic/capchg.html

I think that with a 12V supply, 500 ohm coil and a 470 microfarad
capacitor, the current will will fall to 7.5 mA (3.75V through 500ohm)
in around 0.27 seconds.

Decrease the capacitor to 220 microfarad and you'll get around .13 seconds.

The drain resistor can be worked out using
http://hyperphysics.phy-astr.gsu.edu...ic/capdis.html

I'd go for a large value to delay the time before the button can be
operated again, just in case repeated pulses cause any problems.

Around 390K would discharge to 8.25V in around 30 seconds leaving 3.75V
(12V-8.25V) available again, but would give only a very short pulse if
the button were pressed again. It'll take a few minutes to discharge
enough for a virtually full length pulse though, so you may want to use
a smaller value.

I hope I've got all that right - it's a very long time since I've done this.

SteveW

Steve Walker wrote:

You've mentioned 3.75V, but it's not clear whether that is the pull-in
or drop-out voltage, so I've used it for both and you'll have to adjust
values where necessary.

This should be the pull in voltage, spec sheet says it has to release by
0.5V
snip

Around 390K would discharge to 8.25V in around 30 seconds leaving 3.75V
(12V-8.25V) available again, but would give only a very short pulse if
the button were pressed again. It'll take a few minutes to discharge
enough for a virtually full length pulse though, so you may want to use
a smaller value.

30 second cycle will be fine, it takes 20 seconds to fully open the gate
then it waits 10 seconds before closing, it can be triggered any time it is
clsing to start the opening cycle again.

I hope I've got all that right - it's a very long time since I've done
this.

Thanks Steve I have set up all the bits for a trial ( microswitch in series
with solenoid coil and a bulb across the normally open contacts with 9V pp9
for power), just searching for capacitor and resistor.

AJH

In message , The Natural Philosopher
writes
Bill Wright wrote:
andrew wrote:
I'm looking for the simplest monostable to provide a short pulse to
momentarily close a contact on our electric gate at work. Normally it's
opened with remote control but for visitors during office hours is was
equipped with a bell push for entry and exit, this being cheaper than
induction loops etc.

Some wag has found that if the outside button is depressed and held
down the
gate cycles through open to closed and then will not accept input
from the
other button or the remotes.
I'm after a simple way to have the bell pushes close the contacts
momentarily and then release even if the bell push is held down.

I've got a Crouzet MUR1 that I can get to do the job but it's about
30 quid
and I wonder about something simpler?

AJH
Make the bellpush live, then it will only be held down momentarily.
Bill


simplest is a resistor a capacitor and a pair of CMOS gates.

You might need a buffer with some current to drive anything of any use.

SEE http://www.electronics-tutorials.ws/...onostable.html

and "NOR gate monostable".

Or a NE555 timer. Trigger with a capacitor and fit a pot to adjust the
pulse length.

--
Hugh

"I know not with what weapons World War III will be fought, but
World War IV will be fought with sticks and stones."

Albert Einstein