using current to measure a time
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using current to measure a time
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Panther
Guest
Posted: Thu Dec 01, 2005 4:22 pm    Post subject: using current to measure a time Reply with quote
Hi,

I am making something to measure how much time two objects are in contact
when one of them is accelerated towards the other. To do this, I'm going to
put a wire on one object and another on the other, and make the objects
complete the circuit when they touch obviously. What happens with this is is
these wires link to a stopclock/watch (i can give the model name if you
want) and this stopwatch starts timing when it receives a current and stops
when it receives ANOTHER current. I mean, you give it a current. Starts
time. You "break the circuit." It still times. You give it another current,
it stops. This isn't useful because I need it to start timing when it
receives a current and stop when that current is taken away (as the objects
are no longer in contact; no more current).

What can I do to make this work? Is there anyway I would generate/make a
current come when the circuit is broken? How does a potential divider fit
into this? I am grateful for help. Thank you.

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Dan Hollands
Guest
Posted: Thu Dec 01, 2005 5:35 pm    Post subject: Re: using current to measure a time Reply with quote
Conceptually it is simple

Sense the current that starts the watch

When the current goes away, fire a one shot that will generate a current
pulse to stop the watch

OR

generate a current that is normally connected to the Stop input.

When current is detected switch that current to the Start input until the
current goes away

Other Thoughts

If I had this problem I would simple use an oscilloscope to monitor the time
that the objects touch. If the objects are metalic do you think they will
touch long enough to run a clock?

Dan

--
Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
dhollan3@rochester.rr.com
www.QuickScoreRace.com
"Panther" <black@cat.com> wrote in message
news:dmn80g$p31$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
Quote:
Hi,

I am making something to measure how much time two objects are in contact
when one of them is accelerated towards the other. To do this, I'm going
to put a wire on one object and another on the other, and make the objects
complete the circuit when they touch obviously. What happens with this is
is these wires link to a stopclock/watch (i can give the model name if you
want) and this stopwatch starts timing when it receives a current and
stops when it receives ANOTHER current. I mean, you give it a current.
Starts time. You "break the circuit." It still times. You give it another
current, it stops. This isn't useful because I need it to start timing
when it receives a current and stop when that current is taken away (as
the objects are no longer in contact; no more current).

What can I do to make this work? Is there anyway I would generate/make a
current come when the circuit is broken? How does a potential divider fit
into this? I am grateful for help. Thank you.

Back to top
Nick.
Guest
Posted: Thu Dec 01, 2005 7:54 pm    Post subject: Re: using current to measure a time Reply with quote
On Thu, 01 Dec 2005 16:22:40 +0000, Panther wrote:

Quote:
Hi,

I am making something to measure how much time two objects are in
contact when one of them is accelerated towards the other. To do this,
I'm going to put a wire on one object and another on the other, and make
the objects complete the circuit when they touch obviously. What happens
with this is is these wires link to a stopclock/watch (i can give the
model name if you want) and this stopwatch starts timing when it
receives a current and stops when it receives ANOTHER current. I mean,
you give it a current. Starts time. You "break the circuit." It still
times. You give it another current, it stops. This isn't useful because
I need it to start timing when it receives a current and stop when that
current is taken away (as the objects are no longer in contact; no more
current).

What can I do to make this work? Is there anyway I would generate/make a
current come when the circuit is broken? How does a potential divider
fit into this? I am grateful for help. Thank you.

Blimey... I remember doing those experiments at school on equipment using
Nixies tubes! (Kicking a tinfoil covered football down the corridoor IIRC)

Forget the toy stopwatch. Use (or get) a frequency counter with a "count"
facility. Buy a 1MHz crystal oscillator (example link below). Connect one
object to the osc, the other to the counter input and you have a timer
with 1uS resolution...

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=112331&N=401

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Panther
Guest
Posted: Thu Dec 01, 2005 8:43 pm    Post subject: Re: using current to measure a time Reply with quote
Thanks, but I'm afraid this too complex for me :(

"Andy Baxter" <news4@earthsong.null.free-online.co.uk> wrote in message
news:pan.2005.12.01.18.54.22.316817@earthsong.null.free-online.co.uk...
Quote:
Panther said:

Hi,

I am making something to measure how much time two objects are in contact
when one of them is accelerated towards the other. To do this, I'm going
to
put a wire on one object and another on the other, and make the objects
complete the circuit when they touch obviously. What happens with this is
is
these wires link to a stopclock/watch (i can give the model name if you
want) and this stopwatch starts timing when it receives a current and
stops
when it receives ANOTHER current. I mean, you give it a current. Starts
time. You "break the circuit." It still times. You give it another
current,
it stops. This isn't useful because I need it to start timing when it
receives a current and stop when that current is taken away (as the
objects
are no longer in contact; no more current).

What can I do to make this work? Is there anyway I would generate/make a
current come when the circuit is broken? How does a potential divider fit
into this? I am grateful for help. Thank you.

I don't know if this would work, but you could try doing it like this:

Build a current generator circuit with a fast response rate that didn't
mind trying to drive an open loop.

Connect the output of this to a capacitor through the circuit made by the
two objects.

When they collided, a pulse of current would flow between, and the voltage
on the capacitor at the end would measure the impact time.

--
http://www.niftybits.ukfsn.org/

remove 'n-u-l-l' to email me. html mail or attachments will go in the spam
bin unless notified with [html] or [attachment] in the subject line.
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Panther
Guest
Posted: Thu Dec 01, 2005 8:44 pm    Post subject: Re: using current to measure a time Reply with quote
Quote:
Blimey... I remember doing those experiments at school on equipment using
Nixies tubes! (Kicking a tinfoil covered football down the corridoor IIRC)

Forget the toy stopwatch. Use (or get) a frequency counter with a "count"
facility. Buy a 1MHz crystal oscillator (example link below). Connect one
object to the osc, the other to the counter input and you have a timer
with 1uS resolution...

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=112331&N=401

Thank you for the assistance, but I am not allowed to use that (even if I
was, I wouldn't know how as I'm quite new to this stuff). But thanks anyway.
Back to top
Panther
Guest
Posted: Thu Dec 01, 2005 8:49 pm    Post subject: Re: using current to measure a time Reply with quote
Quote:
When the current goes away, fire a one shot that will generate a current
pulse to stop the watch
What does a one shot mean? Sorry I'm new.



Quote:
generate a current that is normally connected to the Stop input.
When current is detected switch that current to the Start input until the
current goes away

This looks like it would lead to inaccuracies because of slowness. Either
way, I don't think there is a Stop input or anything of that sort.

Quote:
If I had this problem I would simple use an oscilloscope to monitor the
time that the objects touch. If the objects are metalic do you think they
will touch long enough to run a clock?
Unfortunately I can't do that anymore :(


Thanks anyway.
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Nick.
Guest
Posted: Thu Dec 01, 2005 9:20 pm    Post subject: Re: using current to measure a time Reply with quote
On Thu, 01 Dec 2005 20:44:40 +0000, Panther wrote:

Quote:

Blimey... I remember doing those experiments at school on equipment
using Nixies tubes! (Kicking a tinfoil covered football down the
corridoor IIRC)

Forget the toy stopwatch. Use (or get) a frequency counter with a
"count" facility. Buy a 1MHz crystal oscillator (example link below).
Connect one object to the osc, the other to the counter input and you
have a timer with 1uS resolution...

http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=112331&N=401

Thank you for the assistance, but I am not allowed to use that (even if I
was, I wouldn't know how as I'm quite new to this stuff). But thanks
anyway.

You can't use a counter or a 'scope. An analogue (capacitor) solutiom is
too complex. What answer was you hoping for?
Back to top
Panther
Guest
Posted: Thu Dec 01, 2005 9:32 pm    Post subject: Re: using current to measure a time Reply with quote
How I could use a potential divider to set a pulse when the circuit breaks?
Or a more complicated circuit design?

Quote:
You can't use a counter or a 'scope. An analogue (capacitor) solutiom is
too complex. What answer was you hoping for?
Back to top
Panther
Guest
Posted: Thu Dec 01, 2005 9:33 pm    Post subject: Re: using current to measure a time Reply with quote
I'm sorry but this is way too complex for my level. Thanks anyway.

Quote:
Try this: (view in Courier)



GND +5V HFCK
| | |
| [100R] | +-------------+
| | +--|> |
+ +-----A |_ COUNT _| A---+
/ | OR Y---+-O|E Q0 R|O--Y NOR |
/ | +--B | +---------+---+ B---+
/ | | | | |
/ | | A--+ +--A |
/ | +---Y AND NOR Y---+ |
/ | B---------------+--B | | +5v
/ \ / \ | | | |
\_/ \_/ | A---+ | O |
+--Y NOR | |<-ARM
B--------+--O |
|
[1KR]
|
GND


--
John Fields
Professional Circuit Designer
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Andy Baxter
Guest
Posted: Fri Dec 02, 2005 12:54 am    Post subject: Re: using current to measure a time Reply with quote
Panther said:

Quote:
Hi,

I am making something to measure how much time two objects are in contact
when one of them is accelerated towards the other. To do this, I'm going to
put a wire on one object and another on the other, and make the objects
complete the circuit when they touch obviously. What happens with this is is
these wires link to a stopclock/watch (i can give the model name if you
want) and this stopwatch starts timing when it receives a current and stops
when it receives ANOTHER current. I mean, you give it a current. Starts
time. You "break the circuit." It still times. You give it another current,
it stops. This isn't useful because I need it to start timing when it
receives a current and stop when that current is taken away (as the objects
are no longer in contact; no more current).

What can I do to make this work? Is there anyway I would generate/make a
current come when the circuit is broken? How does a potential divider fit
into this? I am grateful for help. Thank you.

I don't know if this would work, but you could try doing it like this:

Build a current generator circuit with a fast response rate that didn't
mind trying to drive an open loop.

Connect the output of this to a capacitor through the circuit made by the
two objects.

When they collided, a pulse of current would flow between, and the voltage
on the capacitor at the end would measure the impact time.

--
http://www.niftybits.ukfsn.org/

remove 'n-u-l-l' to email me. html mail or attachments will go in the spam
bin unless notified with [html] or [attachment] in the subject line.
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Rich Grise
Guest
Posted: Fri Dec 02, 2005 1:35 am    Post subject: Re: using current to measure a time Reply with quote
On Thu, 01 Dec 2005 21:32:18 +0000, Panther wrote:

Quote:
How I could use a potential divider to set a pulse when the circuit breaks?
Or a more complicated circuit design?

You should also learn to bottom-post.

Anyway, I think I have an idea what you want - a current source
that when the balls are touching, lets current flow for time T.

OK, take a power supply, a resistor, a capacitor, and a voltmeter.

PS+ ---- R ----- (B1) (B2) ----+---- Voltmeter +
|
=== capacitor
|
PS- -----------------------------+---- Voltmeter -

Use a high-impedance voltmeter, like a DVM.

Record the voltage while the balls are apart. It will very probably be
very close to zero. You can assure this by momentarily shorting the
capacitor terminals.

Drop the ball. While the balls are in contact, current will flow and
start to charge the cap through the resistor, with a time constant
of T = RC.

The voltage across the capacitor at the exact moment that the balls
separate will tell you T by using that exponential equation that I
can't remember now, but since you're in school you should look it up
anyway.

Good Luck!
Rich

Quote:

You can't use a counter or a 'scope. An analogue (capacitor) solutiom is
too complex. What answer was you hoping for?
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John Fields
Guest
Posted: Fri Dec 02, 2005 1:35 am    Post subject: Re: using current to measure a time Reply with quote
On Thu, 1 Dec 2005 21:33:51 +0000 (UTC), "Panther" <black@cat.com>
wrote:

Quote:
I'm sorry but this is way too complex for my level. Thanks anyway.

---
It seems that no matter how simple we make it, you can't quite get
there.

How about specifying what you want/need in a little more detail, if
you can.

Otherwise, well... we've offed trolls here before.

BTW, here in Rome we bottom post so, when in Rome...


--
John Fields
Professional Circuit Designer
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Big Mouth Billy Bass
Guest
Posted: Fri Dec 02, 2005 1:35 am    Post subject: Re: using current to measure a time Reply with quote
On Thu, 1 Dec 2005 16:22:40 +0000 (UTC), via
<dmn80g$p31$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com>, "Panther"
<black@cat.com> spake thusly:

Quote:
a stopclock/watch (i can give the model name if you want)

Yes, please.
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John Fields
Guest
Posted: Fri Dec 02, 2005 1:35 am    Post subject: Re: using current to measure a time Reply with quote
On Thu, 1 Dec 2005 16:22:40 +0000 (UTC), "Panther" <black@cat.com>
wrote:

Quote:
Hi,

I am making something to measure how much time two objects are in contact
when one of them is accelerated towards the other. To do this, I'm going to
put a wire on one object and another on the other, and make the objects
complete the circuit when they touch obviously. What happens with this is is
these wires link to a stopclock/watch (i can give the model name if you
want) and this stopwatch starts timing when it receives a current and stops
when it receives ANOTHER current. I mean, you give it a current. Starts
time. You "break the circuit." It still times. You give it another current,
it stops. This isn't useful because I need it to start timing when it
receives a current and stop when that current is taken away (as the objects
are no longer in contact; no more current).

What can I do to make this work? Is there anyway I would generate/make a
current come when the circuit is broken? How does a potential divider fit
into this? I am grateful for help. Thank you.

---
I'm assuming you've got two balls hanging from the ends of wires and
you're going to pull on eway from the other and the let it go so
that it'll hit the other one, and what you want to measure is how
long the collision lasts.

Try this: (view in Courier)



GND +5V HFCK
| | |
| [100R] | +-------------+
| | +--|> |
+ +-----A |_ COUNT _| A---+
/ | OR Y---+-O|E Q0 R|O--Y NOR |
/ | +--B | +---------+---+ B---+
/ | | | | |
/ | | A--+ +--A |
/ | +---Y AND NOR Y---+ |
/ | B---------------+--B | | +5v
/ \ / \ | | | |
\_/ \_/ | A---+ | O |
+--Y NOR | |<-ARM
B--------+--O |
|
[1KR]
|
GND


--
John Fields
Professional Circuit Designer
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Nick.
Guest
Posted: Fri Dec 02, 2005 7:04 am    Post subject: Re: using current to measure a time Reply with quote
On Thu, 01 Dec 2005 21:32:18 +0000, Panther wrote:

Quote:
How I could use a potential divider to set a pulse when the circuit
breaks?

You cannnot. A potential divider divides potential.

Quote:
Or a more complicated circuit design?


Some simple designs (e.g. a resister and a capacitor) have already been

suggested but are too complex (?)

If you really must use the stopwatch you mentioned what you really need is
an edge-triggered monostable. You may get away with a simple inverter,
depending on the input logic of the stopwatch. Either way, you will
probably run into problems with "switchbounce".
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