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Example Circuit

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PinkFloyd43

Jan 1, 1970
0
I have a door that needs to be closed all the time, and if it's left
open I want a buzzer to beep for a bit, it could beep constantly till
the door is closed. It's to assure the house animals don't go into my
office which seems to be their favorite place to chew up cables, etc.
Short of getting rid of them I wanted to create some type of alarm
circuit with magnetic switch than when OPEN a buzzer will sound.
Found a couple of the web but they all seem so complicated?

If the door if open for about 20-30 seconds want it to beep!

Thansk!
 
S

Spehro Pefhany

Jan 1, 1970
0
20-30 SECONDS is a bit of a stretch for a 555 timer. I'd run the 555
as a higher-frequency keyed oscillator and use a divider chain to get
a 20-30 second interval.

...Jim Thompson

A CMOS 555 (eg. TLC555/ 7555) will be okay.

But a classic time delay circuit using a 2N6028 PUT to trigger a
2N5064 SCR to drive a DC-powered beeper would work nicely and would
latch on until the power is interrupted (by the door closing again).
Best regards,
Spehro Pefhany
 
J

James Beck

Jan 1, 1970
0
To-Email-Use- said:
20-30 SECONDS is a bit of a stretch for a 555 timer. I'd run the 555
as a higher-frequency keyed oscillator and use a divider chain to get
a 20-30 second interval.

...Jim Thompson

Hell, if/since the amount of time isn't critical, you could use an RC
circuit and a 74C14.
100K res, 220/330uF cap, into one gate the output of that gate can drive
all the left over gates in parallel and their outputs go to a logic
level FET or a transistor. The door switch shorts out the cap when the
door is closed and your done. A 220uF cap will give you ~25sec a 330uF
~40. Use the 330uF and a 100K pot and make it adjustable.
 
R

Rich Grise

Jan 1, 1970
0
I have a door that needs to be closed all the time, and if it's left
open I want a buzzer to beep for a bit, it could beep constantly till
the door is closed. It's to assure the house animals don't go into my
office which seems to be their favorite place to chew up cables, etc.
Short of getting rid of them I wanted to create some type of alarm
circuit with magnetic switch than when OPEN a buzzer will sound.
Found a couple of the web but they all seem so complicated?

If the door if open for about 20-30 seconds want it to beep!

Just use an ordinary switch, so that whenever the door opens, it
buzzes a really obnoxious buzzer right away - this will startle
the animals, and teach them that "open door=>really bad noise".

For that matter, you could equip the door with an automatic closer -
you can get them at the "screen door" section of the home handyman
store. :)

Good Luck!
Rich
 
Hell, if/since the amount of time isn't critical, you could use an RC
circuit and a 74C14.
100K res, 220/330uF cap, into one gate the output of that gate can drive
all the left over gates in parallel and their outputs go to a logic
level FET or a transistor.  The door switch shorts out the cap when the
door is closed and your done.  A 220uF cap will give you ~25sec a 330uF
~40.  Use the 330uF and a 100K pot and make it adjustable.

I can do you one better. Use a resistor and a rather large capacitor
across the buzzer.

Let's see, say the supply is 12V and the buzzer starts at 6V, rated
for 100mA at 12V (= 120 ohms). A series resistor of 60 ohms will give
9V equilibrium, and a Thevenin equivalent resistance of 40 ohms. A
time constant of 30s = R*C gives a capacitance of some 0.75 F, not
actually too unwieldy. Three 2.25F, 2.7V supercapacitors in series
would do.

A DPDT switch on the door turns this on and off. When the door opens,
one set of contacts closes, energizing the circuit. When the door
closes, the other set closes, discharging the capacitor through a
noticably smaller resistor (1 ohm or less?).

Tim
 
J

JeffM

Jan 1, 1970
0
Jim said:
20-30 SECONDS is a bit of a stretch for a 555 timer.
I'd run the 555 as a higher-frequency keyed oscillator
and use a divider chain to get a 20-30 second interval.

If he doesn't need precise repeatability, the 555 would work fine.
With that wide a spec (charging from zero, the first interval of a
*series*
will be 1/3 longer than subsequent intervals),
you could even get it to work for minutes.

The automatic door closer sounds like the ticket.
 
J

James Beck

Jan 1, 1970
0
I can do you one better. Use a resistor and a rather large capacitor
across the buzzer.

Let's see, say the supply is 12V and the buzzer starts at 6V, rated
for 100mA at 12V (= 120 ohms). A series resistor of 60 ohms will give
9V equilibrium, and a Thevenin equivalent resistance of 40 ohms. A
time constant of 30s = R*C gives a capacitance of some 0.75 F, not
actually too unwieldy. Three 2.25F, 2.7V supercapacitors in series
would do.

A DPDT switch on the door turns this on and off. When the door opens,
one set of contacts closes, energizing the circuit. When the door
closes, the other set closes, discharging the capacitor through a
noticably smaller resistor (1 ohm or less?).

Tim
Depending on the annunciator, you could use the 74C14 to direct drive
the bugger and cut out the FET/Transistor and any base/gate resistor you
might need. So, now I'm down to a 74C14, a 100K resistor, and a 220uF
cap. Bet mine is cheaper than yours.

Jim
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
PinkFloyd43 said:
I have a door that needs to be closed all the time, and if it's left
open I want a buzzer to beep for a bit, it could beep constantly till
the door is closed. It's to assure the house animals don't go into my
office which seems to be their favorite place to chew up cables, etc.
Short of getting rid of them I wanted to create some type of alarm
circuit with magnetic switch than when OPEN a buzzer will sound.
Found a couple of the web but they all seem so complicated?

If the door if open for about 20-30 seconds want it to beep!

Thansk!
If you close the door and the door opens by ghosts.Are considering the fact that the animals learned how to open door?Garbage.
 
M

MooseFET

Jan 1, 1970
0
20-30 SECONDS is a bit of a stretch for a 555 timer. I'd run the 555
as a higher-frequency keyed oscillator and use a divider chain to get
a 20-30 second interval.

Use a CD4060. You get an oscillator and a divider all in one. If you
want the alarm to remain on constantly, run a diode 1N914 from the
selected output over to the oscillator's input to force the input high
once the desired output goes high.
 
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