I'd like to build a circuit to turn off
some of the equipment on my fish tank for
maybe 10 minutes during feeding time.

Is there a low-parts-count circuit I can
build to shut off AC power to a socket
for that amount of time when I push a
button?

I've been scribbling with 555's,
comparators, relays, power supplies and
stuff, but I'm wondering if I'm
overlooking something simpler.

All suggestions welcome.

"Randy Day" <r...@shaw.cax> wrote in message 
news:VAAth.782503$5R2.613181@pd7urf3no...

> Is there a low-parts-count circuit I can
> build to shut off AC power to a socket
> for that amount of time when I push a
> button?

120 Volts? You need an industrial delay on timer. You press a button to turn 
it off, another one and after the preset time it will turn on.


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Randy Day wrote:
> I'd like to build a circuit to turn off
> some of the equipment on my fish tank for
> maybe 10 minutes during feeding time.
> 
> Is there a low-parts-count circuit I can
> build to shut off AC power to a socket
> for that amount of time when I push a
> button?
> 
> I've been scribbling with 555's,
> comparators, relays, power supplies and
> stuff, but I'm wondering if I'm
> overlooking something simpler.
> 
> All suggestions welcome.

This should do it for you:

                +--------+--[Relay]---+-------+
                |        |            |       |
                |        +-----|<-----+       |
   ---------    |    __                       d
  | 12V DC +|---+---o  o---+---[1K]---+---+---g
  |WallWart |        PB    |          |   |   s
  | Supply  |              | +        P   |   |
  |         |           [1000uF]   2M O<--'   |
  |         |              |          T       |
  |         |              |          |       |
  |        -|--------------+----------+-------+
   ---------

When you press the PushButton (PB) the N channel
mosfet turns on and the 1000uF cap charges rapidly.
When you release the PB, the charge on the cap keeps
the mosfet conducting. The relay is energized while
the mosfet conducts. The cap slowly discharges
through the 2meg pot. The 1K protects the pot
and the wall wart when the pot is adjusted too
low, and the diode protects the circuit when the
relay deenergizes. Adjust the pot for the desired
delay.  Wire the relay common and normally closed
contact in series with the equipment.

Ed

On Wed, 24 Jan 2007 03:42:45 GMT, Randy Day <r...@shaw.cax>
wrote:

>I'd like to build a circuit to turn off
>some of the equipment on my fish tank for
>maybe 10 minutes during feeding time.

I don't know how much of a load you are talking about.

>Is there a low-parts-count circuit I can
>build to shut off AC power to a socket
>for that amount of time when I push a
>button?
>
>I've been scribbling with 555's,
>comparators, relays, power supplies and
>stuff, but I'm wondering if I'm
>overlooking something simpler.
>
>All suggestions welcome.

Since you've been looking at all that, I won't feel sheepish about
posting a schematic I saw in sci.electronics.design a while back.

>:  
>:              +9V  +9V        +9V              +9V
>:               |    |          |                |
>:               |    |          |                |
>:               |    \          |                |  Pushbutton
>:               |    / R1       |                O  S1
>:               |    \ 33k      |                 \
>:               |    /          |                  \
>:               |    |          |                   \
>:           D2  |    |          |                O
>:       1N4148 _|_   |        |<e Q1             |
>:              /_\   +--------|   2N3906         |
>:               |    |        |\c PNP            |
>:               |    |          |                |
>:               |    \          |                |
>:               |    / R2       +----------------+
>:               |    \ 3.3k     |                |
>:               |    /         --- C1            |
>:               |    |         --- 100uF         \
>:               |    |          |                / R4
>:               |    |          |                \ 470
>:               |    |          |                /
>:               +---------------+                |
>:               |    |          +------,         |
>:               |    |          |      | D1      |
>:               |    |          |      | 1N4148  ))|
>:               |  ||' M1       \     ---        ))| R5
>:               |  ||< BSS145   /     / \        ))| Relay
>:               '--'|,          \     ---        ))| 500 ohms, nom.
>:                    |       R3 /      |         |   200VAC contacts
>:                    |     5.6M |      |         |   normally closed
>:                    |          |      |         |   e.g., SRC devices
>:                    |          |      |         |   PRMA 1B05
>:                   gnd        gnd    gnd       gnd

http://www.srcdevices.com/pdf/dip14ser_src1.pdf

You'd need a 9VDC source, though.  Most folks will recommend that the
9V be isolated from the AC line via a transformer, so there is that,
too.  (You might be tempted to develop the 9V more directly from the
AC line to save the transformer, but keep in mind that pushbutton.)

Since the operating current is about 10mA during that 10 minutes you
want, a 9V battery (nominally, they are spec'd at 25mA) will run for
about 100 hours down to about 5V, which may not be enough to operate
the relay (the one I mention there is available at Digikey for $5.56
in ones, they have stock right now, and it specs a minimum of 3.75V to
operate) for all that time.  But if you get even 20-50 hours out of
it, that may be enough for you.  So a 9V battery would be an option, I
think.

You can use a lower voltage, or higher, but you will need to adjust C1
and R3 to set the timing.  The duration is something like:

  -ln( Vth of M1 / Vsupply ) * R3 * C1

I think the Vth is about 3V for the BSS145, but I haven't checked it.
With Vsupply=9, R3=5.6M, and C1=100uF, I get about 615 seconds delay,
which is close to 10 minutes.

Jon

ehsjr wrote:

[snip]

> This should do it for you:
> 
>                +--------+--[Relay]---+-------+
>                |        |            |       |
>                |        +-----|<-----+       |
>   ---------    |    __                       d
>  | 12V DC +|---+---o  o---+---[1K]---+---+---g
>  |WallWart |        PB    |          |   |   s
>  | Supply  |              | +        P   |   |
>  |         |           [1000uF]   2M O<--'   |
>  |         |              |          T       |
>  |         |              |          |       |
>  |        -|--------------+----------+-------+
>   ---------
> 
> When you press the PushButton (PB) the N channel
> mosfet turns on and the 1000uF cap charges rapidly.
> When you release the PB, the charge on the cap keeps
> the mosfet conducting. The relay is energized while
> the mosfet conducts. The cap slowly discharges
> through the 2meg pot. The 1K protects the pot
> and the wall wart when the pot is adjusted too
> low, and the diode protects the circuit when the
> relay deenergizes. Adjust the pot for the desired
> delay.  Wire the relay common and normally closed
> contact in series with the equipment.

I like it. Thanks.

On 2007-01-24, Randy Day <r...@shaw.cax> wrote:
> I'd like to build a circuit to turn off
> some of the equipment on my fish tank for
> maybe 10 minutes during feeding time.
>
> Is there a low-parts-count circuit I can
> build to shut off AC power to a socket
> for that amount of time when I push a
> button?

yeah, one of those delay buttons: one part.

-- 

Bye.
   Jasen