Help designing an accurate timer (1/100,000 sec) that displays timebetween every other pulse

[Mark Main]

I need to make a timer that will accurately measure (within
1/100,000th of a second) the elapsed time that passed between every
other pulse (the pulses occur between 0.25 seconds and 3 seconds
apart); in other words, it ignores the pulse in between and counts the
time from the START of the first pulse, ignores the second, and
displays the time it took to reach the START of the third pulse.

Then I need the cycle to repeat; so the START of the third pulse is
not only the stop/display trigger, but it’s also a new start trigger
(pulse 1) for the next timing cycle to automatically begin measuring.
So, if it received 10 pulses, it would display the elapsed time
between pulse 1 & 3, 3 & 5, 5 & 7, 7 & 9. If too much time elapses
(overflow) it will be obvious to me and so I don’t need anything fancy
to occur, it can simply display an incorrect time and move on, or wait
for a new trigger to start the timing cycle over, either way is fine,
whatever is easiest.

I’ll need to use a photoconductive cell to generate the pulse
triggers, but the width of the objects passing by can range from 6”
wide down to 1/16” inch and so I need a way to accurately trigger off
of something very thin moving across the beam.

I’ve done some simple electronics projects, but not enough to design
this on my own. Any help is appreciated. It doesn’t have to be
fancy, just accurate, and hopefully somewhat simple to make and
calibrate.

Thank you in advance for any help.
Mark

 

[DaveN]

>
[email protected]...
I need to make a timer that will accurately measure (within
1/100,000th of a second) the elapsed time that passed between every
other pulse (the pulses occur between 0.25 seconds and 3 seconds
apart); in other words, it ignores the pulse in between and counts the
time from the START of the first pulse, ignores the second, and
displays the time it took to reach the START of the third pulse.

So that's 10us, is this the accuracy or resolution you require?

Then I need the cycle to repeat; so the START of the third pulse is
not only the stop/display trigger, but it’s also a new start trigger
(pulse 1) for the next timing cycle to automatically begin measuring.
So, if it received 10 pulses, it would display the elapsed time
between pulse 1 & 3, 3 & 5, 5 & 7, 7 & 9. If too much time elapses
(overflow) it will be obvious to me and so I don’t need anything fancy
to occur, it can simply display an incorrect time and move on, or wait
for a new trigger to start the timing cycle over, either way is fine,
whatever is easiest.

Record the time for all the pulses and then just extract the relevant ones.

I’ll need to use a photoconductive cell to generate the pulse
triggers, but the width of the objects passing by can range from 6”
wide down to 1/16” inch and so I need a way to accurately trigger off
of something very thin moving across the beam.

Ok, what are the objects and what has led you to choosing a photoconductive
cell when you don't seem certain that it is capable of detecting a wide
range of object sizes?

 

[JeffM]

I need to make a timer

Rule #1: Don't build what you can buy.

that will accurately measure (within 1/100,000th of a second)

Go to ebay and buy a counter with lots of digits.

the elapsed time that passed between every other pulse
(the pulses occur between 0.25 seconds and 3 seconds apart);
in other words, it ignores the pulse in between
and counts the time from the START of the first pulse,
ignores the second,
and displays the time it took to reach the START of the third pulse.

One of the first things encountered after AND gates & OR gates.
http://www.google.com/search?q=divided.by.two+f/2+flip-flop+-F1+-F-1+-F/F-2

[. . .]photoconductive cell[...]
the width of the objects passing by can range from 6�
wide down to 1/16� inch and so I need a way to accurately
trigger off of something very thin moving across the beam.

How do you assure that the *objects*
are positioned squarely on the conveyer?
I don't believe you've thought this thru thoroughly.

...and what font are you using
that can't do normal single quotes and double quotes?
I suggest you choose a plain-vanilla one.

 

[Mark Main]

So that's 10us, is this the accuracy or resolution you require?

Accuracy, I'm measuring and displaying time intervals; I just need
them accurately measured.

Record the time for all the pulses and then just extract the relevant ones.

I thought it would be easier to ignore a pulse rather than adding two;
but either way is fine; I'm just seeking the simplest.

Ok, what are the objects and what has led you to choosing a photoconductive
cell when you don't seem certain that it is capable of detecting a wide
range of object sizes?

I've never used photoconductive cells and so I don't know how thin
they can measure, especially at a fast speed. The sender and receiver
will be around 4 inches apart from each other and so if a standard
cell can be triggered from an object 1/16th inch thick passing rapidly
in between them, then that's great... they are more sensitive than I
expected.

 

[Mark Main]

I need to make a timer

Rule #1:  Don't build what you can buy.

that will accurately measure (within 1/100,000th of a second)

Go to ebay and buy a counter with lots of digits.

the elapsed time that passed between every other pulse
(the pulses occur between 0.25 seconds and 3 seconds apart);
in other words, it ignores the pulse in between
and counts the time from the START of the first pulse,
ignores the second,
and displays the time it took to reach the START of the third pulse.

One of the first things encountered after AND gates & OR gates.http://www..google.com/search?q=divided.by.two+f/2+flip-flop+-F1+-F-1+...

[. . .]photoconductive cell[...]
the width of the objects passing by can range from 6"
wide down to 1/16th inch and so I need a way to accurately
trigger off of something very thin moving across the beam.

How do you assure that the *objects*
are positioned squarely on the conveyer?
I don't believe you've thought this thru thoroughly.

Squarely positioned isn't the problem, but I appreciate your
mentioning it. I just need to know the time span accurately between
the START of every other pulse; and the size of the objects can be
quite thin. So I don't know what kind of sensor to detect a break in
a beam spaced about a 4" apart.

 

[Phil Allison]

"Mark Main"

How do you assure that the *objects*
are positioned squarely on the conveyer?
I don't believe you've thought this thru thoroughly.

Squarely positioned isn't the problem,


** Yes it is - wanker.

You cannot get anything like 10uS timing resolution by optical means unless
the objects have SHARP edges and are incredibly precisely aligned and pass
extremely close to the sensor.

The problem is the inherent error in optical position sensing.



...... Phil

 

[Jamie]

I need to make a timer that will accurately measure (within
1/100,000th of a second) the elapsed time that passed between every
other pulse (the pulses occur between 0.25 seconds and 3 seconds
apart); in other words, it ignores the pulse in between and counts the
time from the START of the first pulse, ignores the second, and
displays the time it took to reach the START of the third pulse.

Then I need the cycle to repeat; so the START of the third pulse is
not only the stop/display trigger, but it’s also a new start trigger
(pulse 1) for the next timing cycle to automatically begin measuring.
So, if it received 10 pulses, it would display the elapsed time
between pulse 1 & 3, 3 & 5, 5 & 7, 7 & 9. If too much time elapses
(overflow) it will be obvious to me and so I don’t need anything fancy
to occur, it can simply display an incorrect time and move on, or wait
for a new trigger to start the timing cycle over, either way is fine,
whatever is easiest.

I’ll need to use a photoconductive cell to generate the pulse
triggers, but the width of the objects passing by can range from 6”
wide down to 1/16” inch and so I need a way to accurately trigger off
of something very thin moving across the beam.

I’ve done some simple electronics projects, but not enough to design
this on my own. Any help is appreciated. It doesn’t have to be
fancy, just accurate, and hopefully somewhat simple to make and
calibrate.

Thank you in advance for any help.
Mark

Flip flop ?



--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[Mark Main]

   It ill be very hard to get 10uSec resolution and accuracy with a
photoconductive cell; a silicon photodetector diode is much faster.- Hidequoted text -

- Show quoted text -

I've been looking at adjustable focus laser diode modules on digikey.
All I want to do is accurately measure the elapsed time between every
other pulse regardless of how an object may be twisted slightly, or
whatever... I just need to measure the time from every other pulse
break. And I need it to be able to be as thin as 1/16" and I need the
sending unit and receiver to be about 4" apart, I can get maybe as
close as 3"... possibly slightly closer if I had to.

I also need to figure out how to do an accurate time count.

 

[Mark Main]

"Mark Main"


Squarely positioned isn't the problem,

** Yes it is  -  wanker.

You cannot get anything like 10uS timing resolution by optical means unless
the objects have SHARP edges and are incredibly precisely aligned and pass
extremely close to the sensor.

The problem is the inherent error in optical position sensing.

.....  Phil

I'll design for 10uS and if I get less accuracy due to physical
constraints then I'll have to live with that. I need to do this
optically, and so what would you recommend for an optical solution
that would work at 3" or 4" span between.

 

[Rich Grise]

I'll design for 10uS and if I get less accuracy due to physical
constraints then I'll have to live with that. I need to do this optically,
and so what would you recommend for an optical solution that would work at
3" or 4" span between.

Use a laser diode and photodetector just like the ones that remotes use,
but with a slit over the PHD/PHT. Your accuracy will depend on the speed
of the items, the width of the slit, and the response of the PHD or PHT. A
schmitt trigger could sharpen up the transitions, but you'd have to do
some experimenting with thresholds and stuff, to calibrate it.

And frankly, ten microseconds is a fairly comfortable resolution, given
the electronics they've got these days. ;-)

(PHD == PHotoDiode; PHT == PHotoTransistor.)

Good Luck!
Rich

 

[Rich Grise]

I also need to figure out how to do an accurate time count.

Go to ebay, and buy a counter that has a start/stop interval time
function. Gate the pulses with a little logic, and start/stop the
counter.

Oops - that won't work - I don't know if a boughten counter can stop
the previous count and start the next count simultaneously.

For that, you might need to build - but building a counter isn't
difficult, merely tedious.

Good Luck!
Rich

 

[neon]

with all the variation of packaching speed and still unknown parameters opthical is not the solution it is just too slow

 

[Mark Main]

Use a laser diode and photodetector just like the ones that remotes use,
but with a slit over the PHD/PHT. Your accuracy will depend on the speed
of the items, the width of the slit, and the response of the PHD or PHT. A
schmitt trigger could sharpen up the transitions, but you'd have to do
some experimenting with thresholds and stuff, to calibrate it.

And frankly, ten microseconds is a fairly comfortable resolution, given
the electronics they've got these days. ;-)

(PHD == PHotoDiode; PHT == PHotoTransistor.)

Good Luck!
Rich- Hide quoted text -

- Show quoted text -

Thanks. I see some that there are also some PHT's that can can be
focused... I don't know how narrow the beam is when you do that. I'll
play around with it.

Given the suggestions that I have received, I am going to try and
figure out a way to also display the average of the last 10 cycles and
update this every new cycle. This would require keeping the numbers
stored and doing some math. I'd like to do a 10X and 100X if I can.
That way I can use the 1X mode to tweak the speed, and then shift into
10X and 100X mode to fine tune things.

Now I'll be learning how to store numbers and in a revolving stack of
10 or 100 stored numbers.

 

[Phil Allison]

"Mark Main = another Aspergers fuckwit from Google Groups "



** Mark is a PITA fucking TROLL !!

An imbecile, a fool and a wanker.

IOW - a code scribbler.




..... Phil