Pulse Stretching the extreme case? 1ns to 100ns

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Wond3rboy

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Hi, i was thinking if there was a way by which one could increase the duration of a pulse from 1ns to 100ns. I was browsing through the forum and found this thread

https://www.electro-tech-online.com/threads/pulse-stretching.92764/

it does have a pulse stretcher that can do from 1us to 200us but it does no work for 1ns( and the reason i see is that the output fall/rise time for the 55 timer is 100ns). Is there any other way?

The stretched pulses will be given to a PIC to measure the pulse width. The PIC is an 18F452 running from a 10MHz crystal in HSPLL.

Thanks.
 
Why do you want to determine the duration of a pulse that you have stretched?

Do you just want to detect the presence of the 1ns pulse?
 
Its like the idea of a pic based speed gun. Laser pulses are 1ns and i am supposed to try and detect their reflection. I want to measure the pulse width(done the code with a few glitches)
 
I believe you want to measure the time from the generation of the pulse to the time if its reflected return. The width of the pulse has no useful information.
 
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Oh sorry i meant that. I should have said the time between the pulses. But the problem still is with detecting the pulses.
 
What is the time interval between the pulses you are trying to detect? It's likely that interval is too short for a PIC to measure.

Speed guns usually use the Doppler effect, not time interval to determine the speed.
 
Hi carl, thanks for the replies. I am trying to build a LIDAR and not a RADAR. I was looking at some 680 nm lasers from Frankfurt Laser Company.

Frankfurt Laser Company - SLD (600nm to 800nm)

EDIT: I found this link that is supposed to do the same but the simulation does not do as expected.

**broken link removed**
 
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I haven't simulated it, but I immediately noticed that there needs to be a wire from Q3 base to Q3 Collector, in order for the current mirror to have a chance of working.
 
Hi Carl and Ron, i am using LTspice to simulate the circuit. Had to substitute the opamp in the schematic with one from LTspice. The amplitude of the pulse to detect is around 4.7v.
 
Wond3rboy said:
Hi Carl and Ron, i am using LTspice to simulate the circuit. Had to substitute the opamp in the schematic with one from LTspice. The amplitude of the pulse to detect is around 4.7v.
Click to expand...
Do you know what the source impedance of the pulse is?
Do you really need exactly 100nS width, or does it just have to be slightly greater, in order to detect it with a 10MHz clock?
Speaking of which, 100nS resolution is not very good for measuring speed, is it? At 100 meters, the round trip time for a pulse wil only be about 667nS. Do you have a way of increasing the resolution?
 
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