• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Digital logic question

Status
Not open for further replies.

ethan169

New Member
Ok so I have another question for you guys about a simple logic circuit.

All i really need to do is get a single pulse each time the inputted square wave has a rising edge.

This seems like a pretty simple task to complete to me, I just cant think of the logic that is needed. My first thought was something with a counter or Flip-Flop.

I found this article - Triggering Off Both Rising & Falling Edge of TTL Signal to Create a Square Wave with Double the Frequency - National Instruments

And here they are basically using two counters to double the frequency of a supplied square wave by triggering on both rising and falling edge.

I just need something like the Ctr 1 out in this article.

Its basically just configuring a counter to provide a pulse at the output on the rising edge of the input. What counter could i use to do this?

I took digital all to long ago and unfortunately didn't pay much attention.

Thanks for any help guys!

-Ethan
 

Chippie

Member
an edge triggered monostable....a 555 timer chip would do..

Look at the link, about two thirds of the page down...

555 timer

Number 8 in the sequence..
 
Last edited:

KMoffett

Well-Known Member
The circuit is an "edge detector". Attached using CMOS version. R2/C1 sets the output pulse width. SW1 just simulates the input square wave.

ken
 

Attachments

ethan169

New Member
The 555 timer circuit looks like it defiantly does the job that i need.


But Heres a question on the edge detector circuit.
The circuit is an "edge detector". Attached using CMOS version. R2/C1 sets the output pulse width. SW1 just simulates the input square wave.

ken
This will give me a pulse on both the rising edge and the falling edge. How would i modify this to be just rising edge?

-Ethan

btw thanks for the quick responses!
 

ronsimpson

Well-Known Member
Most Helpful Member
74HC123 can be set for rising or falling edge but will not respond to both. Time is set by RC.
 

monkeybiter

Member
a small capacitor coupled to a pull down resistor on the target might be adequate, I've used it to latch a 74xx573 in the past.
 

ccurtis

Well-Known Member
The attached gives a very short positive pulse on the output for each rising edge on the input.
 

Attachments

Status
Not open for further replies.

EE World Online Articles

Loading
Top