detect pulse of 140ns and 50mv.

[hiren.dave@bhuved.com]

Hi,

i want to detect a pulse with 140ns and 50mV amplitude. i want to design such a circuit when pulse comes pic microcontroller should get an interrupt. how can i do that?

thanks in advance...

 

[Nigel Goodwin]

You need to amplify the pulse to make it bigger - but more details are required.

I don't know how long a pulse needs to be to guarantee it triggers an interrupt?, possibly the datasheet will tell you? - if it's too short a simple pulse stretcher would be needed (but again, it depends on exactly what you're trying to do).

 

[hiren.dave@bhuved.com]

thanks, friend.

i used amplifier and pulse stretcher but it detects a pulse of only 1 us. beyond this i can't get good response..

 

[Nigel Goodwin]

thanks, friend.

i used amplifier and pulse stretcher but it detects a pulse of only 1 us. beyond this i can't get good response..

Post the circuit you've used - and what the source is.

 

[hiren.dave@bhuved.com]

hi,
the source is photodiode.
currently i am using lm 324 / lmc6482in ic for opamp and HCF4098b pulse stretcher that can stretch a pulse. but i am not getting a pulse. is these IC are good enough ? Should i buy another one? please suggest me...

 

[Mikebits]

post your schematic

 

[alec_t]

The LM324 is too slow for amplifying a 140nS pulse. Try a high-speed opamp.

 

[hiren.dave@bhuved.com]

hi,

i am giving my circuit below. in which photodiode output is given to amplifier than pulse stretcher with led.
View attachment 66953View attachment 66954



now, i have changed my opamp to MC33274AP (on semiconductor) and pulse stretcher is CD4098BE(texas).

 

[alec_t]

now, i have changed my opamp to MC33274AP

And what was the result?

 

[jpanhalt]

Maybe this is the problem:

View attachment 66955

You are at 5V and minimum trigger width is 140 ns.

John

 

[hiren.dave@bhuved.com]

currently i am testing circuit with opamp MC33279p and i am giving 12V to my pulse stretcher...

 

[WTP Pepper]

On the analogue side, a simple high speed op-amp comparator will do. You bias the reference minus some from the incoming signal. 140nS catch circuit using a basic 74HC4538/74HC121 monstable is very straight forward to give an input to the PIC. Can post an LTSpice sim when I get around to it.

 

[Mikebits]

How did you determine your pulse width is 140ns?

 

[hiren.dave@bhuved.com]

hi friends,

Finally i got the pulse using MC33274AP opamp and cd4098 pulse stretcher. thanks to all for being with me.

 

[WTP Pepper]

How did you determine your pulse width is 140ns?

Let me see....Maybe from the title of the thread - detect pulse of 140ns and 50mv.

 

[Mikebits]

Let me see....Maybe from the title of the thread - detect pulse of 140ns and 50mv.

Clever.
Since the OP made this statement:

hi,
the source is photodiode.
currently i am using lm 324 / lmc6482in ic for opamp and HCF4098b pulse stretcher that can stretch a pulse. but i am not getting a pulse. is these IC are good enough ? Should i buy another one? please suggest me...

I am curious what photo diode outputs a 140ns pulse. What test instrument did he use to make this determination?

 

[hiren.dave@bhuved.com]

hi,

photodiode gives output when low power laser falls on it.i determine pulse voltage and timing with calculation. i measured big pulse in cro and according to those readings, i got this small pulse.

 

[Mikebits]

hi,

photodiode gives output when low power laser falls on it.i determine pulse voltage and timing with calculation. i measured big pulse in cro and according to those readings, i got this small pulse.

I don't know of any photo diode that can operate at that speed. Please share the data sheet.

 

[hiren.dave@bhuved.com]

it's BPW 34.



www.vishay.com/docs/81521/bpw34.pdf