Are you ready for a challenge?

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I agree it is a lot different. When I first started I was assuming that I could measure the time of the pendulum by passing the object swinging through or by some device to trigger my timer. But there is also another way, I could attach a thin object to the pivot point and let that object break the light path also. Either one will work equally well. My period will be about 1 second and all I need to do is use the photogate to start and stop a timer. It would be great if the timer had a sensativity of 1 ms but 1/100 sec is fine.

If I were to use the one that I have in the picture above I would use an adapter on the pivot pin and use the photogate to detect with the adapter passed by. If I had a way to measure the pendulum directly the gate would have to have an opening of about 12". If I used UV paint all I need to do is place the LED close to the pendulum. Any method would work.
 

hi,
Does your PC have a 'free' parallel printer port or 9pin serial.??

EDIT:
I could attach a thin object to the pivot point and let that object break the light path also

A possible problem with this would be as the travel 'arc' is greatly reduced the accuracy would be impaired.
The light beam and detector path would have to be reduced to a slit...
 
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Eric you have changed (Avatar) you are not getting mad are you? LOL

ericgibbs said:
hi,
Does your PC have a 'free' parallel printer port or 9pin serial.??
...
Click to expand...

No but I could get one that does. Also I would prefer to have a stand alone unit anyway. If someone else used this application that may be a show stopper.


I agree the preferred method would be to have the detector just below the very bottom of the pendulum. But with this method I have to have a wide spread on a photogate or use RV paint. The farther I go up the less he arc and the more accuracy is impaired.
 
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Allow me think out loud here for a minute Eric. Let's assume the the length from the pivot to the bottom of the pendulum is 20", and if I were to attach an object to the pivot it would be measured 2" out from the pivot. The object's arc would be 1/10 the arc of the bottom of the pendulum but the speed of the object would be 1/10 the speed of the bottom of the pendulum too. So I am not so sure the accuracy would be off from that standpoint.

But because of the slower or faster speed it could introduce problems in the detector. That object could protrude out as far and 4" or 5" there reducing the arc to 1/5 or 1/4 the bottom of the pendulum. Any of these ways are good for me.
 
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M10SINV said:
. But there is also another way, I could attach a thin object to the pivot point and let that object break the light path also. .
Click to expand...

you are right, you can use the interupter with a thin object attached on the top of the pivot, you can make a hole on the object so your sensor will be inversely used, ie: it will be unblocked only at a certain point when the hole comes in line.

another way i already told you is as attached, this case you can use a reflective tape on the top of the pivot edge so it will not make any considerable error on your centre of mass.

edit: you can use 4017 counter instead of a processor to do all what you want basically.
 

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mbarazeen said:
...another way i already told you is as attached, this case you can use a reflective tape on the top of the pivot edge so it will not make any considerable error on your centre of mass...
Click to expand...

Yes I could but that top edge will be about 4" above the pivot. I could use RV paint at that location possibly but some times the top of the pendulum is hollow. I will check into the 4017
 
mbarazeen said:
...you can use 4017 counter instead of a processor to do all what you want basically.
Click to expand...

I think you are right but let me make sure I understand you. I am going to have to use 4 counters to get a.xyz and each counter will need to advance the next (z>y>x>a) until the 1 ms trigger is stopped
 
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