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.
--
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 | |
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.
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
On Thu, 1 Dec 2005 16:22:40 +0000 (UTC), via , "Panther" spake thusly:
Yes, please.
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
--- 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
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...
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.
What does a one shot mean? Sorry I'm new.
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.
Unfortunately I can't do that anymore :(
Thanks anyway.
You can't use a counter or a 'scope. An analogue (capacitor) solutiom is too complex. What answer was you hoping for?
How I could use a potential divider to set a pulse when the circuit breaks? Or a more complicated circuit design?
I'm sorry but this is way too complex for my level. Thanks anyway.
You cannnot. A potential divider divides potential.
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".
--- It seems to me that by your not cross-posting, by your off-handed rejection of several solutions which have been presented to you, and by not using in-line references, you're not really looking for a solution to your "problem", but instead are more interested in playing games.
Am I wrong?
-- John Fields Professional Circuit Designer
-- How do you propose to do the practical without the equipment?
T = RC is the "time constant". It's the amount of time it takes for the charge to reach 63% (or something) of its final value, R is in ohms, and C is in farads. With T on the horizontal axis, the cap voltage rises at some exponential rate... Maybe one of these sites will be more helpful:
Good Luck! Rich
Thank you!!!!!!!!!!!!!! This looks very simple so I will give it a go. But could you please explain what the time constant T = RC means? I've no idea. So you're saying, for example, if I were to do the practical now and record the voltages, I would be able to work out the time section using some formula? IE I don't need the equipment? As that would very handy.
Thanks
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