# NOT/OR gate for 9 volt

Discussion in 'Electronic Basics' started by mail4happy, Feb 5, 2004.

1. ### mail4happyGuest

I have a gate that cost me an arm and a leg. I don't want the daughters
backing into it as they try to navigate out the driveway. I want to have a
horn go off if the gate is not fully closed or not fully opened. A 9 volt
battery would run the buzzer/horn while the gate is in the transition state
of closing/opening. The only way I can figure to wire this up is:
IF [Not (closed)] OR [NOT (opened)} THEN Horn
ELSE no horn

or maybe

If [Closed] OR [Opened] Then No Horn
ELSE NOT [output-> circuit to
horn]

This would allow me to have two contact closures, one at each end of sliding
gate...BUT it also require both NOT gates and OR gates....!

How is this done?

Tom Johnson
Baldwin Park, California

2. ### Don A. GilmoreGuest

Hi Tom:

You're making this way harder than it needs to be. All you need is two
normally-closed switches: one that breaks when the gate is open and one that
breaks when the gate is closed. Wire them in series between the positive
side of the battery and the horn. Wire the negative side of the battery
directly to the horn.

When the gate is open or closed, one of the switches will break the circuit
and the horn will not sound. If the gate leaves either switch, it will
close and turn the horn on until either switch breaks the circuit again.
With a circuit like this you could even use a 120 Vac whoop-siren! That
ought to get their attention!

3. ### MichaelGuest

Use two normally closed contacts in series with the buzzer (like the
light switches in a fridge), so that when the gate presses them at
either end it opens the circuit and stops the buzzer.

If you wanted to improve on that, you could put a beam accross the
driveway so the buzzer only sounds if they approach the gate.

4. ### RobertGuest

I am guessing this is what you require,

Horn will only go off when gate is either not closed or not open. So
when ever it is closed or open it wont horn right?

all that is required then is just a single NOR gate, one input
indicating Closed and one indicating Open, don't know how you will
implement those signals but that is all you require.

Hope that helps

Rob

5. ### John FieldsGuest

---
Or an OR or an AND or a NAND or two mechanical switches wired in
series, which is the RIGHT way to do it as you might have found out if

You're guessing that what's running around in that peabrain of yours
is what he needs, and you don't have a clue as to how he's going to
hook it up to make it work, but for some reason you felt compelled to
grace the group with your profound insight.

Why????

6. ### Don A. GilmoreGuest

Boys....where's the love?

Don

7. ### SteveGuest

Forget the logic gates. I would go with "normally closed" reed
switches, and a strong magnet attached to the gate in an appropriate
place. Or perhaps you'll need two magnets; hard to say without seeing
the gate in situ!

(Actually, which state is "normal" for a reed switch. Does normally
closed mean that it's closed when it's NOT affected by a magnet? Or
is the other way around?! Seems like a vague description to me.)

Have the 9V wired through one switch, then the other, then to the
buzzer/horn.

Gate fully closed, magnet opens one switch, no current.

Gate opening, both switches closed, BZZZZZ!

Gate fully open, magnet opens other switch, no current.

Is this an electric gate? Perhaps you just need to tap into the
voltage supply to the open/close motor!? Probably works on the same
principal as what I've described.

niftydog

8. ### John FieldsGuest

---
Probably 99% of the reed switches manufactured are what is known as
"Form A" which means that the contacts are normally open when not in the
presence of a magnetic field. This presents a problem in that the
switches want to be closed _except_ when the gate is fully open or fully
closed. Not an intractable problem, however, but rather one that can be
easily solved with the use of bias magnets. What is done is that the
bias magnets are located near each switch (to hold the switches closed),
and the gate carries another magnet which, when it approaches either
switch, cancels the field of the bias magnet. This forces one switch to
open when the gate is fully open and the other to open when the gate is
fully closed. Reed switches are also a good idea because they're
impervious to the weather and this sounds like an outdoor application.

9. ### JeffMGuest

I want to have a horn go off
|
+--------+
| ___|__
/ | | /
\ |BUZZER| /
/ |______|/
\ |
| |/
+--+------|
| |
\ |>
\ |
o |
| |
\ |
\ |
o |
| |
+-----------+
N.C. __|__
REED SWITCHES ___
(MAGNETS ON _
DETENTS)