Turn off delay circuit

[vic]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

Thanks.

 

[Phil Allison]

"vic"

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on the
subject ?

** Google " NE555" .

Gets about half a million hits.


.... Phil

 

[[email protected]]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

Thanks.

Depending on the volatge and current involved, you could be talking
about a CMOS 555 timer or as thermal delay relay.

What voltage?

How much current?

Batteries or mains power?

John

 

[Allen Bong]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

Thanks.

Take a look at the recent discussion on SEB on 24th Feb. The link is
at

http://groups.google.com/group/sci.electronics.basics/browse_thread/thread/e2f9392cdea86c89#

3 versions of solutions using transistors, NE555 and PIC are
available.

Allen

 

[Allen Bong]

Take a look at the recent discussion on SEB on 24th Feb.  The link is
at

http://groups.google.com/group/sci.electronics.basics/browse_thread/t...

3 versions of solutions using transistors, NE555 and PIC are
available.

Allen

Further down on post #88, the problem can be sloved by op-amp as well
as suggested by John Field.

The PIC software posted by nobody for the delay timer was for
something else and has to be reworked.

Allen

 

[Jamie]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

Thanks.

Look for the 555 timer, It has 2 inputs, trigger and threshold that are
part of a RS (Reset/Set) flip flop circuit.
Pulling the trigger low will latch the output on, pulling the
threshold high will unlatch the output. etc.

It's smaller and more versatile than employing a flip flip chip when
you only need one switch. On top of that, you can also place some timing
activity in that same lay out.


http://webpages.charter.net/jamie_5"

 

[vic]

"vic"


** Google " NE555" .

Gets about half a million hits.


... Phil

Thanks for your precious advice. I was not clear enough. Let me explain
again : at first, the circuit is completely powered off. The user pushes
a button, which injects power into the circuit. Then a mechanism
maintains the power active, even if the switch has been released. At a
later undetermined moment, when the circuit does no longer need power,
it cuts its own power and sleeps until the user chooses to push the
button again. I'm pretty sure a 555 can't do this.

vic.

 

[Phil Allison]

"vic"

Thanks for your precious advice.
I was not clear enough.

** YOU are bout as clear as mud - fuckhead.

And that situation is certainly congenital.

Let me explain again : at first, the circuit is completely powered off.
The user pushes a button, which injects power into the circuit. Then a
mechanism maintains the power active, even if the switch has been
released. At a later undetermined moment, when the circuit does no longer
need power, it cuts its own power and sleeps until the user chooses to
push the button again. I'm pretty sure a 555 can't do this.

** **** knows WHAT THE HELL you are blathering about.

Whatever it is - you are way off topic here.

This NG is only about BASIC electronic concepts, hardware and practices.

Try " alt electronic.gadgets-wankers " instead.




...... Phil

 

[vic]

Look for the 555 timer, It has 2 inputs, trigger and threshold that are
part of a RS (Reset/Set) flip flop circuit.
Pulling the trigger low will latch the output on, pulling the
threshold high will unlatch the output. etc.

It's smaller and more versatile than employing a flip flip chip when
you only need one switch. On top of that, you can also place some timing
activity in that same lay out.

Sorry I really did not phrase my question well it seems. By "power on"
and "power off", I meant really the power to the circuit, maintaining
power while needed and cutting its own power after the desired action
has been performed. It is intended to save as much power as possible
when the circuit doesn't do anything.

A 555 circuit would not do since it would need to be powered on permanently.

That's why I said a FET would do. Probably any other transistor, but the
FET is closer to my energy saving goal. Here's what I imagined :

.------------------------.
VCC o-+------+ +----+ |
| --- | "Slave Circuit" |
| ^ | |
| | | |
| / | | Something here keeps |
+--/ o--+----+ the FET conducting |
| | as long as needed. |
.-. | |
| | | |
| | | |
'-' | |
| | |
| | |
GND o----------+----+ |
'------------------------'

When the user presses the switch, the circuit is powered and in turn
pulls the FET gate up. The user can release the switch at this time. At
some other time in the future, the circuit decides it does no longer
need power and lets the gate go down, cutting power and hopefully
consuming zero current. I need to figure out if this would work and what
kind of transistor to use.

vic.

 

[Nobody]

Sorry I really did not phrase my question well it seems. By "power on"
and "power off", I meant really the power to the circuit, maintaining
power while needed and cutting its own power after the desired action
has been performed. It is intended to save as much power as possible
when the circuit doesn't do anything.

Version 4
SHEET 1 1100 680
WIRE 192 -544 64 -544
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WIRE 176 -176 64 -176
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WIRE 560 -176 384 -176
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WIRE 560 -32 560 -176
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WIRE 800 48 800 -176
WIRE 560 144 560 48
WIRE 64 272 64 -176
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WIRE 384 496 64 496
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SYMBOL voltage 64 256 R0
WINDOW 123 0 0 Left 0
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SYMATTR InstName Rcoil
SYMATTR Value 100R
SYMBOL voltage 256 -400 R0
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SYMATTR Value PULSE(-1 1 1s 0 0 0.2s)
SYMBOL csw 176 -176 R270
WINDOW 0 32 40 VTop 0
WINDOW 3 -32 40 VBottom 0
SYMATTR InstName W1
SYMATTR SpiceModel Vsense
SYMBOL voltage 384 -128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName Vsense
SYMATTR Value 0
SYMBOL res 784 32 R0
SYMATTR InstName Rload
SYMATTR Value 1K
SYMBOL sw 176 -544 R270
SYMATTR InstName S1
SYMBOL npn 448 272 M0
SYMATTR InstName Q1
SYMBOL res 544 -48 R0
SYMATTR InstName R2
SYMATTR Value 10K
SYMBOL cap 544 144 R0
SYMATTR InstName C1
SYMATTR Value 470µF
TEXT 176 536 Left 0 !.model CSW CSW(Ron=1R,It=50mA, Ih=10mA)
TEXT 176 584 Left 0 !.model SW SW()
TEXT 174 632 Left 0 !.tran 10s

 

[bw]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on the
subject ?

My microwave oven does that. It uses no power when off. The timer is
mechanical.

 

[ehsjr]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

Thanks.

Here's a generic circuit to show the idea:

N/O N/O
+12 ---+---o--- Rly1-1 Rly1-2 ---o---+
| ^---o------+ +---^ |
o | | +--- To your
o | +-------------- circuit
| |
+----->|----------+
| ___|___
+---[R]---+---| 555 |
| | | |---+----+
| | | | | |
| | ------- | |k
| /c | [Rly1] [D1]
+--[R]---| | | |
\e | | |
| | | |
Gnd -------------+-------+-------+----+

Use a 555 as diagrammed (not a schematic, just to present
the idea) above. The pushbutton causes the npn to put
a negative on the 555 trigger, and provides plus to the
555 while it is pressed. The 555 output goes high, and
operates the relay, which takes over the role of providing
+ to the 555. The 555 stays high for however long you
set it, then drops, removing power. No reason you have to
use a relay - you can use the idea with a fet or bipolar if
you want.

More important: the asumption is that you want a timed delay.
However, that may not be the case. You might, for example,
have a motor that opens and closes a window, and you want the
circuit to run until the window is fully open (or fully closed),
then shut off. Or a circuit that is indended to bring temperature
up to some point, then shut off. The problem is that the subject
of your post says "delay", but the requirement specifies that
some action has been completed. So to make it a bit more
generic:
S1 or Sensor
+12 ---+---+ N/C
| |
| V
| -------o---- Rly1-1 N/O
| o---^
| |
+----o o---+
|
[Rly1]
|
Gnd --------------+

S1 is a microswitch or a sensor that interrupts the circuit
when the action is complete.

Ed

 

[Phil Allison]

"vic the prick "

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

** So it's a toaster - right ??




..... Phil

 

[Robert Monsen]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

Thanks.

Use a PMOS fet as a pass element. Connect the source to the input
voltage, and the gate to the input voltage through a 1MEG transistor.
Use the drain as the supply for your circuit.

Have two connections to the gate of the FET, one to a normally open
switch connected to ground, and the other to a port on your
microcontroller.

Push the button to power up. When the uc initializes, have it set the
port to 0 output.

When you want the circuit to turn off, have the uc set the port to
high impedance.

Regards,
Bob Monsen

 

[MooseFET]

Hi,

I'd like to design a circuit such that it is powered on by a short press
of a switch, performs some action, and then turns itself off when it has
done its purpose.

I suppose I could do this using a FET, but it has surely been done
millions of times and I'd like not to reinvent the wheel. Could you give
me a suitable example of such a circuit, or resources to inform me on
the subject ?

PNP or PMOSFET
Vin--+---- ----------
! e\ /
! ----
! !
-/\/\-+
!
\
/
\
! N-MOSFET
----+-!!
! !!--------------Port on micro
PB ! O -!!
--! !
! O GND
!
GND