# Question on Logic Gates

Discussion in 'Electronic Basics' started by vicebay, Oct 27, 2004.

1. ### vicebayGuest

Hi, I would like to ask if anyone know a circuit or an IC that has
the following characteristic.

single input -- single output

The output should only be triggered by a positive (1) input and will
not change even if the input changed it state to 0. But when the
input changed in state to 1 again, the output should change in state.

I would like to implement this on my design in a sequential light.

TIA

-vicebay

2. ### Rich GriseGuest

The assignment is to implement one with gates. If it
were me, I'd use a master-slave arrangement, because I've
never been able to figure out how to toggle one. But I
can toggle a 2-transistor, emitter-coupled flip-flop.
Go figure. ;-)

Cheers!
Rich

3. ### JamieGuest

yes.,
they call it a flip flop.
A D type will work with its DATA
input connected to an out.
a RS, or JK also..
the output will be a logic 5 or
what ever depending on what family
of logic chip you use.
you most likely want to use something
like a TTL, HC or CMOS into a transistor/
a HexFet works well for this.

4. ### Terry PinnellGuest

Here's a circuit using Jamie's suggested approach:
http://www.terrypin.dial.pipex.com/Images/4013FF.gif

5. ### petrus bitbyterGuest

The circuit you describe is known as a divide by two circuit. It's a part of
almost all counters but can be made easily out of a single flipflop. One of
the oldest and wellknown is the 74LS74. Although this days a CMOS successor
like a CD4013B may be a better choice. Just connect the inverted output of
the flipflop - /Q or an "overscored" Q - to its D-input. Then the Clock
input of the flipflop is your input and the Q output of the flipflop is your
output. Hope you have the skills to build your sequential light.

petrus bitbyter

6. ### Randy DayGuest

But you've got the input connected to the Q output.
That'll let the magic smoke out.

I assume you meant for the input to go to the
clock pin in the middle?

7. ### Geir KlemetsenGuest

"Terry Pinnell" <> skrev i melding

- cut -
And this is an alternative:

.---------------------.
| |
| | Output
| .--o--. |
.-----. | .-----|J S Q|-----o--------o
| G | | | -|> | __ __
|_-_-_|----------o---)-----|K R Q|o ---. __ __ __
| | | '--o--' |
'-----'Input | |
| |
'-----------------'
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

8. ### Geir KlemetsenGuest

Eh, of course. I was a little bit fast here.