A little help with JK flip flops and counters!

Discussion in 'Electronic Design' started by [email protected], Mar 11, 2006.

1. Guest

Hello,

I'm currently working on a project for my university course where I'm
required to design a circuit that will count cars in and out of a car
park. We have to use components in the LS41 series.

All I'd like to know is, is there a way to make a (JK flip-flop)
counter count up or down, or would I need, say, two separate counters
(One for cars going in, one for cars going out)? I was thinking of
having two counters (that reset *at some point*) that plug into an
adder to determine what number of cars are in the car park (This data
will then goes into an encoder for a LED display). Is there a flaw in
my logic?

The ultimate goal of the project is to display a "FULL" sign when there
are no spaces left, but I have an idea how to do that.

Also, I'd like to know the purpose of the 'J' and 'K' in a JK
flip-flop? In all the examples I've seen, they're both set to HIGH and
left at that.

Many Thanks

2. Fred BloggsGuest

I'm currently working on a project for my university course where I'm
Setting both JK HIGH makes it into a TOGGLE FF and this is the building
block of a RIPPLE counter where either the Q or /Q of the JK is used as
the CLOCK of the next stage JK depending on whether the IC
implementation uses positive or negative clock edge triggering. For the
parking lot application a single counter can be used as an INTEGRATOR.
Cars entering increment the counter and cars leaving decrement the
counter. There must be external control so that when in all 0's state
further decrement pulses due to cars leaving are locked out, and when in
all 1's or some other state representing maximum capacity further
increment pulses are inhibited and the FULL sign is lit. This assumes
there is an entrance gate. If there is no entrance gate then the counter
requires OVERFLOW capacity, the FULL sign is lit when the counter
increments past maximum capacity, increment pulses are never inhibited
in any state, FULL sign is extinguished when counter decrements below
maximum capacity.

3. Guest

Fred Bloggs,

Thank you for your prompt reply, but could you expand on what you mean
by an 'INTEGRATOR'? I've had a look for further explanation and cannot
find anything!
Does it take the form of some kind of component that you insert before
the counter, or is it implemented within it? Thank you for your time, I
am relatively inexperienced with electronic design and appreciate all

Also, for clarification - in my initial post I stated I was using
components in the 'LS41 series'. Clearly I'm talking rubbish! I meant
'74LS'!

4. Tim WescottGuest

How To Design With Parts:

Step 1: Find a data sheet.

Step 3: Think.

If you find a data sheet of a JK flip flop in the series you're looking
at (surely you mean 74LS?) you'll see what all the inputs do -- clear,
J, K, clock and (if it's there) preset.

Have they troubled to show you Karnaug maps yet? If not do a web search
(and pardon my spelling) or look in your logic textbook. You should be
able to go from first principals to design an up/down counter using JK
flip flops and gates. You should also be able to grab a 74LS series
data book and find an up/down counter, but that's your problem.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

5. Tim WescottGuest

Integrator, in this context, means a digital accumulator that simulates
integration (is in the funny stretched 's', the 'dt' at the end, and all
the hair lying around that you pulled out trying to solve it).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

6. RST Engineering \(jw\)Guest

Is that an absolute requirement? 74LS is a rather antique and obsolete
technology. So is 4000 series CMOS, but it is a hell of a lot easier in
CMOS than TTL.

I'm presuming that you are "given" a sensor of some sort with a pulse
output?

Jim

We have to use components in the LS41 series.

7. Guest

You don't need two counters. What you need is an up/down counter.
Google it and you'll find lots of design mostly using JK flip-flops.
One common place to "steal" a circuit is from a datasheet. Find an
up/down counter chip in any of the logic family, like the 74HC169 for
example, and look up the datasheet. You'll usually find a simple
schematic to explain the operation of the chip.

8. Fred BloggsGuest

As a general term, integrator means to make many as one. In this case
the "many" is the entire previous history of increment and decrement
pulses to the counter and the "one" is the counter state at one
particular point in time which represents the net count of cars in the lot.
If you look at the sequence of binary patterns, the up/down RIPPLE
counter is especially easy to make from JK FFs.