A digital circuit question

[jb885]

I have a circuit and when I press a button I get a logical 1, and I want only through logic to output a single 1 and then only 0s without releasing the button.( so when I press the button I get 1 and then only zeros)

 

[alec_t]

A 555 timer IC perhaps?

 

[jb885]

well, I know I could use a 555 but can it be done with logic?

 

[alec_t]

Yes. Use a monostable.

 

[crutschow]

For a relatively long pulse you either need a monostable, such as a 555 or CD4047, or a couple of JK flip-flops with a clock source.

If the pulse can be short, on the order of tens to a few hundred nanoseconds depending upon the logic family, then you can use the delay through an odd number of inverter gates plus a two-input AND gate to generate a one-shot pulse equal to the sum of the inverter delays. Connect the series inverter string output to one AND input and the input control signal to the both the inverter string input and the other AND input.

 

[jb885]

4 clock cycles delay

Hi,

How can I create a 4 cycle delay using flip flops/counters/LFSR??? I don't want to use a 555 or any external IC. Just logic elements. Basically an external source, i.e a button will trigger the first flip flop, possibly by getting the CE of the first flip flop to be high and I want the sequence:

Output 1
then
output 4 cycles 0
then
output 1
then 4 cycles 0
and so on

I'm not sure if this is a delay but I want the sequence above triggered by a constant logic 1 (from the button when pressed)
The button will be still pressed.
Please answer me in schematics or description and not in VHDL

 

[colin55]

Use a 4017

 

[dr pepper]

As above 4017 clocked by the 555, connect Q0 to your output, then connect Q5 to reset, that'll give your function, the on time for Q1 will be the same as the 555's period.

You could arrange the pushbutton to hold the 555 and 4017 in reset when not pressed, you'd need a transistor inverter for that as the 555 has a not reset input and the 4017 a reset input.

 

[alec_t]

Is this a homework question?
I suggest googling 'johnson counter'. You'll get hits such as
https://www.google.co.uk/imgres?img...eRT7qCN8Hg8gOCh_C6BA&ved=0CD4Q9QEwAA&dur=1438

 

[jb885]

Thanks for the reply but how could I do this without a 555 or an IC?? Just flip flops

Thanks

 

[alec_t]

how could I do this without a 555 or an IC?? Just flip flops

You can't do it with 'just flip-flops'. You need logic gates as well. Look at the picture in that link. It shows how flip-flops and gates are connected to make a counter.