Need help in a project

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Ali Inam

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Hi, I am making up a Velocity Counter using a photo diode. I have planned it to be in the following way:

I will be having two ends, on both of those ends I will be having photo diodes on one side and laser lights falling on the diodes from exactly opposite sides. Now I will make a toy car move, once the toy car intercepts the first light beam, I want my counter to start the time immediately and as soon as it intercepts the other beam, I want it to stop.


Can anyone guide me please.

Thanks....!!
 

hi,
How wide will the distance from the 'laser' to photo-diode be?

How accurate do you want the timing, what will be the maximum expected count.

What units do you want to display in, secs, tenths sec etc.??
 
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I think the laser would probably be 6 to 10 inches away from the photo diode. And the distance between the two photo diodes must be around 1 meter I think so the time involved in that would just be seconds. Thats what I might be needing I think......
 
Ali Inam said:
I think the laser would probably be 6 to 10 inches away from the photo diode. And the distance between the two photo diodes must be around 1 meter I think so the time involved in that would just be seconds. Thats what I might be needing I think......
Click to expand...

hi,
For such a short distance a laser emitter would be an overkill, a IR emitter driven by a 555 timer circuit would be good enough. The 555 and transistor could drive both the start and finish emitters.

If you used a TSOP detector for the receiver it would help minimise ambient light problems.

EDIT:
A modified version of one these circuits could be used for the timing and display.
https://www.electro-tech-online.com...asic-3-digit-led-decade-up-down-counter1.html
 

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Ali Inam said:
Yes yes I can
Click to expand...

OK,
Would a 2 digit display be suitable, this would give from 00 to 99 seconds.

Two CD40110 IC [ which ar old types] would be a simple circuit to build, check if you are able to get these at your location.
If you cannot buy this type, look for alternative BCD UP counters and LED driver IC's, let me know.
 
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