using a current to measure a time interval

Probably belongs on sci.electronics.basics

If you can provide a link to the stopwatch that would help.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Jim Thompson
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Are the two currents SEPARATE inputs; or a single input, where first occurrence starts, second occurrence stops ??

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

That is the ENTIRE relevance. How does the timing device work? Specifications? Your link gives no clue.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

[snip]

How long (typically) is the event you're trying to time?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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.

Reply to
Panther

I posted it there too.

The device is a UNILAB Stopclock (513.051)

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I can't find anything more unfortunately :|

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Reply to
Panther

I'm not sure I completely understand what you're saying (sorry, I'm new to this stuff), but basically I have two wires that touch to make the current flow and let go when the objects stop touching each other. So I guess single input?

There are two inputs on the device btw, if that is of any relevance.

Thank you

Reply to
Panther

Basically, from the link I gave you, the picture at the top is it. But there's a centrisecond timing module that can be attached to where the three inputs are at the bottom. There's a toggle switch on the centrisecond module thing with two options

- clock controlled by input A

- clock controlled by inputs A and B

From the manual: "The stopclock can be controlled by connecting mechanical switches across the three terminals. These switches can be remote from the Stopclock. A momentory short between terminals 2 and 3 will either START or STOP the clock. Many switches can be arranged in parallel.

There is a picture that might be helpful:

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The circled bits are meant to be switches I think.

This is the circuit I made which gave the result I said in my first post:

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Sorry if that is of no help, but I can't really see anything else. Also this timer module is commonly used with light gates, as a pulse of light or something turns the timing on, and another pulse turns it off. Unfortunately my investigation doesn't function similarly.

Thanks.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Reply to
Panther

Forget about the stopwatch. Just integrate the current with an RC circuit and measure the voltage in the C after the contact. It will give you a measure of the total time that the circuit was completed.

This approach has some problems of its own. The biggest one is that you would need a very low-leakage capacitor and voltage sensing circuit, and/or a means of capturing that voltage before it has time to bleed off (like a fast A/D).

-Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

Hmm. I would say probably below 2 seconds. It's really two trolleys like these:

formatting link

So I guess the time of contact would be very short, probably less than a second.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Reply to
Panther

Certainly not going to be easy. Collisions like this can produce MULTIPLE contacts. Ever seen high speed photos of automobile collisions?

Maybe you should conduct this experiment first:

+5V to first wire

Resistor from second wire to ground

Observe top of resistor with a _triggerable_ oscilloscope (storage would also be nice) and see what you get.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Jim Thompson

--
For _you_ maybe...

>Collisions like this can produce MULTIPLE contacts.
Reply to
John Fields

Good point, but the OP seems hung-up on using the timer. Probably a requirement set by the lab instructor ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

--
The critical problem with that method is determining when the event
ended and setting in motion the chain of events leading up to the
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Reply to
John Fields

Exactly why I suggested the analog approach of integrating the current in an R/C circuit and then measuring the voltage quickly after the event before the C has time to discharge.

-Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

That depends on what the OP really wants to measure. If he wants to measure total contact time, even if the time is in several discontiguous periods, then integrating is fine. Exact determination of when the event ended is not necessary. The only limitation is that if you wait too long, the charge will start to bleed out of the capacitor. But if you wait a "reasonable" time after the last contact and measure the voltage it will represent the total contact time.

However, if the OP wants to measure the total time from first contact to last contact release, then my method fails. Something digital would have to be used. And even then some awkward thresholds would have to be set to determine how short of a contact counts as a "real" contact.

-Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

THANKS!! Just to confirm, you can work out the time by measuring voltage, right by using a formula that requires no practical (after working the voltage, of course).

Also what is a low-leakage capacitor? Is it called anything on the market? In schools? And how would I capture that voltage before it goes. That sounds hard.

Reply to
Panther

Polypropylene is good. Look at the specs in the Digikey catalog.

Use an A/D converter. If this is a one-off project, get an off-the-shelf board from Measurement Computing. But you will need to make a custom voltage buffer first. A FET-input op-amp is good for that.

-Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

Not at all, after you've completed your coursework.

Good Luck! Rich

Reply to
Rich Grise

If all you want to know is how long the objects bang into each other then you can use something like shown below. You use the timer to calibrate your BREAK time- which defines "end of collision." For example, you may not care about short durations breaks in the collision as long as the contact continues to occur- and you define end of collision on a final break of contact. You define and set the time for this final break of contact duration using the CAL momentary and the timer. RST the timer, press CAL, note the time, adjust ADJ BREAK, and repeat until you have reasonable time like 100ms. It may be difficult to adjust exactly, so if the timer shows 101.05s you would record this time. Then RST the timer, set up, and conduct your collision. This will produce a reading on the timer of say 315.08s. Your total collison time is then 315.08-101.5=214.03ms. This means the trolleys continued contact with no break larger than 101.5ms for a duration of 214.03ms. This is the duration of collision and not necessarily actual contact time which may not be important. View in a fixed-width font such as Courier.

. . 3-6V . | Vbatt . .-----||---+----------+-----------------------. . | | | | | . | | | EXOR | ____ . com +-----||---+ | ____ +--\\ \\ \\ . | 100n | .---\\ \\ \\ | | |G3 >---. . | | | | |G2 >----|--/ /___/ | . | | | .-/ /___/ | | . | C1 | | | | | . | .----------||------+ | | | | . | | 220n | | | | | . | | | | | | | . | | .----[100K]----+ | | | | . | | | | | | | | . | | | _ | | '-------------|-------. | . | | | /| | | | | | . | | [5M] | | | | | . | | /| BREAK | | | | | . | | | ADJ | | | | | . | | | | | | | | . | | | ---------U1 | ---------U2 | | . | | | | VCC/RST | | | VCC/RST | | | . | '---+-----. | | | | | | | . | | .-|THRESH OUT|-+-[150K]+--|THRESH OUT|-' | . .-------+--[100]-+-+ | | | | | | . | | | '-|TRIG | +--|TRIG | | . CON-o | | | | C2| | | | . TACT | | | GND | === | GND | | . o | | --------555 100n -------555 | . | | | | | | | . '---+---------------------+---------------+-------+com | . | | | . | 1N914A ------- | | . '----------|>|---. | START|-------. | | . | | /STOP| | | | . Vbatt | | | \\| | | . | | | | 2N3904|---|--[10K]------' . .-----------+-------. | | UNILAB|

Reply to
Fred Bloggs

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