Simple Low to High OR High to Low Detector?

Thread Starter

Jacobpaul21

Joined Aug 12, 2020
5
I have basic digital circuit knowledge, but I'm a little new, so I apologize in advance for some ignorance.

I'm looking for a simple design or integrated circuit chip that can detect when an incoming signal changes from low to high OR high to low. Each time it detects this change, I want it to send out a brief HIGH signal as an output. Being able to detect multiple inputs (rather than just detecting 1 of these changes at a time) would be most helpful. Does anyone know of anything like this that exists? If so, any and all help is greatly appreciated!

Jacob
 

Thread Starter

Jacobpaul21

Joined Aug 12, 2020
5
I may need to check with my advisor regarding how many inputs we need to check, but this is such a smart and simple idea of going about it. Thank you so much!
 

AnalogKid

Joined Aug 1, 2013
8,606
Note: This is an image grab off the innergoogle to show the concept in post #2. This is *not* a complete solution for the TS because we don't have enough information.

1597249209509.png
ak
 
Last edited:

Thread Starter

Jacobpaul21

Joined Aug 12, 2020
5
If you need to stretch the pulse, consider adding a one-shot to output "B".
I haven't worked with one-shots, but I looked them up and this seems like something I would want to incorporate to my circuit. Do you have any design ideas or integrated circuit chip recommendations? I'm going for simplicity and smallest footprint over price, if that helps at all. Thank you for your help!
 

Papabravo

Joined Feb 24, 2006
14,435
I haven't worked with one-shots, but I looked them up and this seems like something I would want to incorporate to my circuit. Do you have any design ideas or integrated circuit chip recommendations? I'm going for simplicity and smallest footprint over price, if that helps at all. Thank you for your help!
Here is a CMOS chip that will operate over a wide supply rage
https://www.ti.com/lit/ds/symlink/cd4098b.pdf?ts=1597341012265&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FCD4098B

Here is one in CMOS technology with a narrower supply range
https://assets.nexperia.com/documents/data-sheet/74HC_HCT123.pdf
 

Papabravo

Joined Feb 24, 2006
14,435
The main thing to remember about one-shots (aka Monostable Multivibrators) is that the trailing edge may not be a precise time from the rising edge. It will be the calculated time ± a little bit. In most applications this is not a problem. Also, retriggering is sometimes a handy feature and sometime it is not.
 

Papabravo

Joined Feb 24, 2006
14,435
The pulse width is determined by the XOR input RC time-constant (assuming the input stays high or low longer than the desired pulse-width..
I agree that there is some latitude in choosing the pulse width by adjusting the RC time constant. There may be drawbacks to using that method for larger pulse widths. If the RC time constant can do the job then fine, if not there is an alternative with considerable flexibility.
 
Top