Hey guys.

I am trying to turn a short pulse into a logic high for +/- 3 ms (see file/drawing attached). I got this working with a 555 timer, pretty much a clap-on circuit. The problem is I need to detect 3 different pulses, separately and I am having problems using 3 x 555 timers from the same power supply. The threshold I need is so sensitive that I get some false triggers from leak or something. So I have been looking at the NE558 which is a quad timer, but I cant seem to get any good info online on how the pin configuration works and how I would set the threshold.

http://www.mantech.co.za/ProductInfo.aspx?Item=35M1317

Has anyone maybe used this IC that can give me some pointers?

Thanks in advance.

 

hi,
Do you have a circuit diagram you could post.?
E

 

hi,
Do you have a circuit diagram you could post.?
E

For the 555 circuit I used this
https://www.google.co.za/search?q=555+timer+clap+switch&tbm=isch&source=iu&ictx=1&fir=tQ5ATrKrcgM06M%3A%2CcsSTQGKJ4WtjZM%2C_&usg=AFrqEzePGHdSR65t9BMMpE1AV3uws573HQ&sa=X&ved=2ahUKEwiHl8PblPvcAhXJA8AKHQp1DzgQ9QEwAHoECAUQBA#imgrc=tQ5ATrKrcgM06M:

(hope that link works, but it is the first google result) For the NE558 nothing yet.

 

hi,
On your built circuit, did you have any decoupling capacitors on the power lines.?
E
RSA PE.

EDIT:
Have you seen these two 558 App PDF's

 

Thanks EG

I have tried the de coupling caps, but I am hobbiest and I might have done it wrong. Thanks for the pdf, the data sheet I found on the 558 is terrible..., will go through that first one and post my findings. Thanks again.

 

For future reference this could be done with a single chip, something
like this. In fact its almost a code-less design, requires one line of code to
start the comparator. I used PSOC 5LP (got lazy), should be able to imp-
lement in PSOC 4 low end part.

I set the trigger at .256V, could be anything you want using a R divider
external or internal DAC.




Regards, Dana.

 

Note this rejects noise as well -



Regards, Dana.

 

Thanks Danadak, but I don't have PSOC and I need to do this using a standalone chip. It is outside the scope of the original question.

 

hi,
Looking at your initial drawing, it shows the input pulses at different amplitudes.
What are the amplitudes and period of these pulses.?
E.

 

I understand. Note the PSOC is a standalone one chip solution for the
entire problem, all 3 channels. Or 16 if thats needed. Also does not need
a bunch of external timing passives.And accuracy of timing pulse generated
much better than 555. And trigger threshold not sloppy, eg. derived from
Vdd, unless thats what you prefer.

Consider for future designs

Regards, Dana.

 

hi,
Looking at your initial drawing, it shows the input pulses at different amplitudes.
What are the amplitudes and period of these pulses.?
E.

Eric, I will send a screenshot of my scope as soon as I get home, but the amplitude is "irrelevant" as I only need to catch the very first part of the wave form and ignore the tail-end, meaning I just need to know when the pulse started. What I can say is that it is a very short pulse, +/- 1ms before it completely dies out. I will try to make a more complete drawing...

 

hi,
OK, so at some level just above zero volts you want to generate a pulse.
If you want to use IC's, the LM393 is a good low cost dual comparator.
E

 

Exactly correct. Awesome, thanks. I will have a look at that IC

 

Hi

After going through that documentation and trying the ne558, I discovered that my problem is actually not the timer, but the fact that my pulse sometimes starts with a negative voltage and sometimes positive and the trigger is thus not accurate. This changes the scope of my initial question, so I started a different thread:

https://forum.allaboutcircuits.com/...ion-in-positive-or-negative-direction.151622/