Dual 555 Timer Delay Circuit Help

[Terry]

Searched the web everywhere and can't find a circuit that will do
this.

Want a sensor to activate the trigger on a 555, and then the sensor
won't reactivate the trigger on the first 555 until the delay period
set by the second 555.

Trying to hack a PIR for a halloween prop. Want the sensor to activate
the 555 and the output trigger the prop and then delay the next
activation so some kid in a group doesn't stand there and keep
triggering the sensor.

Only thing I could find is that possibly need to use the second 555 to
activate the Reset of the first 555 during the second's timing cycle
to prevent a re-trigger.

Any help is appreciated.

Terry

 

[Hal Murray]

Want a sensor to activate the trigger on a 555, and then the sensor

won't reactivate the trigger on the first 555 until the delay period
set by the second 555.

Trying to hack a PIR for a halloween prop. Want the sensor to activate
the 555 and the output trigger the prop and then delay the next
activation so some kid in a group doesn't stand there and keep
triggering the sensor.

Are you happy writing software? How about a low end CPU?

 

[Tam/WB2TT]

Searched the web everywhere and can't find a circuit that will do
this.

Want a sensor to activate the trigger on a 555, and then the sensor
won't reactivate the trigger on the first 555 until the delay period
set by the second 555.

Trying to hack a PIR for a halloween prop. Want the sensor to activate
the 555 and the output trigger the prop and then delay the next
activation so some kid in a group doesn't stand there and keep
triggering the sensor.

Only thing I could find is that possibly need to use the second 555 to
activate the Reset of the first 555 during the second's timing cycle
to prevent a re-trigger.

Any help is appreciated.

Terry

Terry,
Check out the 74HC4538 dual monopulser. You can fire both off at the same
time, and then not allow a new trigger until the longer pulse has timed out.
There is also a CD4538 equivalent, but I don't think it is CD. Ones I used
had Moto numbers. Depending on how you strap the inputs, it is either
retriggerable, or not retriggerable.

Tam

 

[Robert Monsen]

Searched the web everywhere and can't find a circuit that will do
this.

Want a sensor to activate the trigger on a 555, and then the sensor
won't reactivate the trigger on the first 555 until the delay period
set by the second 555.

Trying to hack a PIR for a halloween prop. Want the sensor to activate
the 555 and the output trigger the prop and then delay the next
activation so some kid in a group doesn't stand there and keep
triggering the sensor.

Only thing I could find is that possibly need to use the second 555 to
activate the Reset of the first 555 during the second's timing cycle
to prevent a re-trigger.

Any help is appreciated.

Terry

Use a 100k resistor from the sensor to the common trigger line. Then,
connect a diode from the output to the trigger input.

input ----/\/\/\----o-----triggers
|
_
^
|
output from longer 555

When the input is pulled low the first time, it'll trigger both 555s.
However, once it does that, the output of the second one will bring the
trigger line high again (through the diode) until its done.

After the second one finishes, it'll drop its output, allowing more
triggers to start it over again.

This is a general way to make a 555 non-retriggerable.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Ken Smith]

Want a sensor to activate the trigger on a 555, and then the sensor
won't reactivate the trigger on the first 555 until the delay period
set by the second 555.

A portion of the circuit:


------
! !
---/\/\/\-+--!TR Q!-----+---- To load
! ! ! !
--- ------ ---
^ ---
! ------ !
! ! ! !
---!Q TR!-----+
! ! !
------ /
\
/
!
Vcc

 

[Terry]

Thank you everyone for the help. Considered a MCU for this, but
overkill for something so simple. Had the 555's so wanted to use them.
I am up and running now using the output running back to the first
trigger.

Terry